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36c3 preroll music
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Herald: So who is excited about[br]photography or videography?
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applaus[br]Herald: Yeah? The title of the talk kind
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of gives us gives it away. OK. We bet we[br]are waiting for the last people to come in
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and take a seat. Last time, raise your[br]hands if you have a free seat next to you.
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Every one of you coming in, look for raised hands[br]and take your seat and then we will start.
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Yeah, very good. OK. Looks like the doors[br]are finally closed. Okay, so the next talk
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on the second day is about ultrafast[br]imaging. So many of you have done
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videography or photography. Have thought[br]about exposure time, how fast you can do
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your photography. And some of your might[br]have played with lasers and have built
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blinky stuff with it or have done[br]scientific experiments and Caroline Will
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now show us what happens if we take those[br]to combine them and take it to the
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extreme. Caroline is working at DESY since[br]four years. She has not done her PhD and
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is now working in a group for theoretical[br]fast modeling of inner workings of
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molecules and atoms. She is doing a[br]computational work and working together
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with experimentalists to verify their[br]observations, and now she is presenting
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the inner mechanics of what she is doing[br]and how we can actually maybe photograph
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molecules by their forming. Applause!
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applause
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Caroline: Great. Yeah. Thank you very much[br]for the introduction and thank you very
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much for having me here. I'm excited to[br]see this room so full. So I'm going to
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speak today about an ultrashort history of[br]ultrafast imaging. It's a really broad
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topic. And I'm just gonna present some[br]highlights, some background. Before I
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start, I'd like to give you a few more few[br]more words about myself. As we've already
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heard, I work at DESY, this is the DESY[br]campus you see here and in the Center for
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Free Electron Laser Science, circle in[br]orange. That's where I did my PhD. So this
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whole campus is located in Hamburg. This[br]is probably also a familiar place to many
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of you. And now this year we are in[br]Leipzig a bit further away for the 36th
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Congress. So I'd like to start with a very[br]broad question. What is the goal of
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ultrafast imaging? And we've heard already[br]that ultrafast imaging is related to
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photography. Now, as many of you know,[br]when you take a picture, with a quite long
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exposure time, you see just a blurry[br]image, for example, in this picture of a
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bowl of water. We can hardly see anything.[br]It looks a bit foggy. But if we choose the
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correct exposure time, which in this case[br]is 100 times shorter in the right picture
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than in the left picture, then we see a[br]clear image and we can see dynamics
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unfold. So we have here, a drop of water[br]that is bouncing back from the bowl and
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also some ripples that are forming on the[br]surface of this bowl. This is only visible
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because we chose the right exposure time.[br]And this is to me really the key of being
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successful in ultrafast imaging to take a[br]clear picture of an object that is moving.
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But it's not enough to say take just a[br]picture. So now imagine you're a sports
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reporter. You get these two pictures and[br]you're supposed to write up what happened.
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So it's complicated. So the top picture is[br]the start, the bottom pictures is the end.
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Just from these two pictures, it's hard to[br]see. But if we see before picture, we can
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see very complex dynamics unfold. There[br]are particles accelerating at high
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velocity laughing coming in from the back. And even[br]particles we did not see in the first
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picture at all somehow are very relevant[br]to our motion. And not only skiing races
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are very dynamic, but most processes in[br]nature are also not static. This is true
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for everything we see around ourselves,[br]but it's especially true for everything
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that is quite small in the microcosm. And[br]in general, we can gain a lot more insight
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from time resolved images. So from ultra[br]short movies. I'd like to show you the
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very first ultrafast movie that was ever[br]taken. Or maybe even the first movie that
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was taken at all. This guy, Eadweard[br]Muybridge lived in the 19th century. And
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very shortly after the invention of a[br]photography method, he tried to answer the
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question does a galloping horse ever lift[br]all of its feet off the ground? Why, it's
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running. To us, it may seem like not so[br]important question, but in the 19th
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century, the horse was the main method of[br]transportation, and horse races were very
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popular. So there was a lot of interest in[br]studying the dynamics of a horse, and this
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process is too fast to see with the naked[br]eye. But Muybridge implemented a stop
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motion technique where the horse as it is[br]running, cuts some wires, that then
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trigger photographs. And with this he was[br]able to take these twelve photographs of
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the horse in motion. That was published[br]under this title in Stanford in the 19th
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century. And we see very clearly in the[br]top row third picture and maybe also
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second picture that indeed the horse lifts[br]all of its legs off the ground, which was
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a new insight at that time. And when we[br]stitch all of these snapshots together, we
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have an ultra fast movie of a horse[br]galloping, which might be seen as the
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first movie that was ever made in the[br]history of mankind. Now, when I say
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ultrafast today, I'm no longer thinking[br]about horses, but about smaller things and
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faster things. But let's go there, very[br]gently. So the time scale that we are all
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familiar with that we can see with the[br]naked eye is something of the order of
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seconds. So, for example, the acceleration[br]of this cheetah, we can see with the naked
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eye. Now, if we zoom in on this motion, we[br]see that there are muscles inside of the
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animal that are contracting as it is[br]running. And this muscle contraction takes
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place within milliseconds. So that's a[br]part of a thousand in one second. But we
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can go even smaller than that to the[br]microsecond. So proteins inside of the
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muscles or in any biologic matter fold and[br]unfold on a timescale of microseconds.
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That's already a part in a million of a[br]second. Now going even smaller, to
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nanoseconds there's certain dynamics that[br]take place within these proteins, for
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example, of how they dissolve in water.[br]But the timescale that I'm interested in
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today is the femtosecond. It's even faster[br]than that it's the timescale where
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individual atoms move in molecules as[br]shown in this animation. Now a
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femtosecond is very short. It's a part in[br]a million of a billion of a second, or as
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we physicists like to call it, ten to the[br]minus 15 seconds because it's easier to
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spell laughing to us. We can - to us - , we can go even[br]faster than that. The time scale of
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electronic motion and in molecules would[br]be an attosecond. I'm just mentioning it
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here because we don't stop at molecules,[br]but nature is even faster than that. But
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for the purpose of this talk, I will[br]mainly focus on processes that take place
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within the femtosecond. So within ten to[br]the minus fifteen seconds. Now, this time
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scale is something that is not really[br]related to what we think about in everyday
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life. But there are certain processes in[br]chemistry, biology and physics that are
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really fundamental and that start at this[br]time scale. Just to give you an idea how
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short a femtosecond is, the width of a[br]human hair is about 100 micrometer. It's
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shown here in an electron microscopic[br]picture. And for light at the speed of
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light, it takes only thirty femtoseconds[br]to cross the hair. So that's how fast a
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femtosecond is. And even although this[br]timescale is so short, there are many
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important processes that start here, I'd[br]like to mention, just two of them. The
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first one is vision in our eyes and our[br]retina there sits a molecule called
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rhodopsin, that is shown here to the left.[br]And when light hits rhodopsin, it starts
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to isomorphise, which is a fancy word for[br]saying it changes its shape. And this
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transmits, in the end, electrical impulses[br]to our brain, which enables us to see. And
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this very first step of vision takes only[br]two hundred femtoseconds to complete. But
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without it, vision would not be possible.[br]Another very fast process that is
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fundamental in nature is photosynthesis,[br]where plants take light and CO2 and
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convert it to other things, among them[br]oxygen. And the very first excitation
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where light hits the plant and it starts[br]to make all this energy available. That
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also takes less than one hundredth[br]femtoseconds to complete. So really the
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fundamental questions of life lie at this[br]timescale. And I'd like to just mention
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that all of these processes are not only[br]very fast, but they also take place in
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very small objects, that are of a size of[br]a few atoms to nanometers, which makes it
0:10:11.540,0:10:15.480
also hard to observe because we cannot see[br]them with the naked eye or with standard
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microscopes. Now, we've seen already that[br]it's important to choose the right
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exposure time to get a clear image of[br]something that's moving, but the kind of
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method that we need for taking such a[br]photograph of something that is moving
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depends a lot on the timescale. So for[br]stuff that is moving within seconds or
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fractions of a second, we can see that[br]with the naked eye, we can use cameras to
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resolve faster motion, very much like[br]Muybridge did with the very first camera.
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Today, of course, we can go much faster to[br]maybe a few microseconds. With very fancy
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cameras called opto-electronic street[br]cameras - i won't go into detail here - we
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can go down to picoseconds. So we are[br]already very close to the motion of
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molecules, but we are not quite there yet.[br]The timescale that we want to investigate
0:11:06.899,0:11:11.060
is a femtosecond. So really a time[br]timescale of molecular motion and
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electronics are not fast enough to reach[br]this timescale. So we need something new.
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And fortunately, we can create light[br]pulses that serve as to say flashes, but
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take snapshots of our moving molecules[br]with femtosecond time resolution and light
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pulses can be made so short. So in the[br]following, I'm going to show you a bit
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more detail on how we can use these ultra[br]short light pulses to take snapshots of
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moving molecules. The first method that I[br]would like to briefly show you is X-Ray
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diffraction, where we have an ultra short[br]pulse, an X-Ray pulse coming in. It hits a
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sample shown here in the red bubbles.[br]That's essentially a molecule that that we
0:11:54.899,0:12:01.541
just place in the beam and it produces a[br]so-called diffraction pattern that we can
0:12:01.541,0:12:07.829
then record on a screen. Now, the whole[br]process is quite complicated. So I like to
0:12:07.829,0:12:15.420
just sketch the very basics of it. We see[br]here X-Ray radiation hitting a crystalline
0:12:15.420,0:12:23.040
sample here to the left and the sample is[br]excited, starts to radiate X-Ray back and
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on the right we can see the X-Rays leaving[br]the sample again. They will interfere and
0:12:29.199,0:12:34.670
we can record this pattern on the screen.[br]So this is what we see here in this
0:12:34.670,0:12:42.570
visualization to the right. With this, we[br]can feed a reconstructionalgorithm that
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allows us to transform back our[br]diffraction pattern that we've seen here
0:12:47.110,0:12:53.570
for for in this case a bio molecule. We[br]can reconstruct from that the image as it
0:12:53.570,0:13:00.899
was in real space. So this is some[br]protein, I believe. X-ray diffraction is
0:13:00.899,0:13:09.149
very nice for resolving small structures[br]with atomic detail. Another method how we
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can take snapshots using ultra short[br]pulses, that I would like to briefly
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introduce is absorption spectroscopy. Now[br]you may know that light contains several
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colors. For example, you've surely have[br]held a prism in hand, and the prism can
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break white light up into all the colors[br]of a rainbow, that we can see with the
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eye. Now we can do the same with X-Ray[br]pulses. Then we cannot see the colors
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anymore. So just let's just stick with a[br]prism here. When we place a molecule in
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front of all these colors, the molecule[br]will block certain colors. That's quantum
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mechanics. You just have to believe it or[br]learn about it in long studies. So the
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molecule is placed in front of all these[br]colors. And to be right, the absorption
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spectrum is recorded and the parts of the[br]spectrum that are very bright correspond
0:14:08.110,0:14:14.480
to the colors that have been blocked by[br]the molecule. And this is a very nice
0:14:14.480,0:14:19.089
technique to investigate ultra short[br]dynamics, because where these lines are
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located is characteristic of the chemical[br]elements that we find in the molecule. For
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example, if we use X-Ray radiation for[br]this specific molecule, that I've shown
0:14:28.760,0:14:33.810
here lysine, that's not so important which[br]molecule it is. We have three different
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atoms in this molecule that are important[br]carbon, nitrogen and oxygen and they
0:14:39.269,0:14:43.880
absorb at very different colors so we can[br]keep them apart when we take the spectrum.
0:14:43.880,0:14:49.120
But not only that, we can take the[br]spectrum at a later time when the molecule
0:14:49.120,0:14:54.420
has moved around a bit and we will see[br]that the colors, the position of the lines
0:14:54.420,0:14:59.829
have changed a tiny bit. So it's really[br]not much and I accelerated it already in
0:14:59.829,0:15:06.070
this visualization quite a bit. But with[br]experimental methods, we can resolve this.
0:15:06.070,0:15:11.420
And this allows us to then trace back to[br]how the molecule was moving in between
0:15:11.420,0:15:16.889
when we took these two snapshots. There[br]are many more methods that you can use to
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take ultrafast images. So we call them[br]probe signals because we probe the
0:15:21.820,0:15:26.889
ultrafast motion of a molecule with such[br]an ultra short pulse. For example, we can
0:15:26.889,0:15:33.009
record photo electrons or we can record[br]fragments of a molecule and many more. But
0:15:33.009,0:15:37.519
I won't go into further detail here[br]because this is not an exhaustive list of
0:15:37.519,0:15:42.320
methods that we can use. I'd rather like[br]to show you how we can take molecular
0:15:42.320,0:15:47.709
movies so how we can combine all these[br]ultrashort pulses to in the end film a
0:15:47.709,0:15:55.050
molecule in action. Now we've already seen[br]in the movie of the horse that we need to
0:15:55.050,0:16:00.990
stitch several snapshots together and then[br]we have a full picture, full motion of a
0:16:00.990,0:16:06.740
molecule. So we just like to do the same,[br]but ten to the 15 times faster, should not
0:16:06.740,0:16:13.029
be too difficult, right? So we use our[br]ultra short pulse. First ultrasound parts
0:16:13.029,0:16:17.980
that we use as a trigger, parts that sets[br]off the motion and the molecule. This
0:16:17.980,0:16:22.410
defines us a certain time zero in our[br]experiment and makes it sort of repeatable
0:16:22.410,0:16:28.300
because we always start the same kind of[br]motion by giving it a small hit and now
0:16:28.300,0:16:34.870
it's just moving around. So we wait for a[br]certain time, a time delay and then come
0:16:34.870,0:16:40.940
in with a probe pulse. The probe pulse[br]takes a snapshot of a molecule. This goes
0:16:40.940,0:16:45.320
to some detector, goes to a kind of[br]complicated reconstruction method that we
0:16:45.320,0:16:51.709
just execute from our screen. And with[br]this, we reconstruct a snapshot of a
0:16:51.709,0:16:56.850
molecule. But this is only one snapshot[br]and we want a whole movie. So we need to
0:16:56.850,0:17:02.240
repeat this process over and over again by[br]shining and more and more probe pulses.
0:17:02.240,0:17:08.040
And this will create more and more[br]snapshots of a molecule. And in the end,
0:17:08.040,0:17:12.209
we could stitch all of these together and[br]we would arrive at the same image that you
0:17:12.209,0:17:18.430
see in the in the middle where the[br]molecules is happily moving around. There
0:17:18.430,0:17:24.790
is one little problem: The probe pulse[br]typically destroys the molecule. This is
0:17:24.790,0:17:28.500
very different. This is very different[br]from taking pictures of a horse. The horse
0:17:28.500,0:17:36.289
normally survives. laughting So the probe pulse[br]destroys the molecule. It just goes away.
0:17:36.289,0:17:41.830
So for each of these snapshots we need to[br]use a new molecule. So we typically have a
0:17:41.830,0:17:47.970
stream of samples that is falling from the[br]top to the bottom in our experiment. And
0:17:47.970,0:17:51.690
then we have to carefully align two pulses[br]a trigger pulse and a probe pulse that
0:17:51.690,0:17:57.610
come together and take a snapshot of this[br]molecule. And of course, we have to find a
0:17:57.610,0:18:03.120
method on how to make identical molecules[br]available in - Yeah - you see, there's a
0:18:03.120,0:18:07.860
lot of complications with doing these[br]experiments that I'm completely leaving
0:18:07.860,0:18:15.090
out here. So now we want to take a[br]molecular movie and we know that we want
0:18:15.090,0:18:19.700
to have ultra short pulses to do so. But I[br]didn't tell you yet what kind of light
0:18:19.700,0:18:24.750
source we need. So there are many light[br]sources all around us. We have here lights
0:18:24.750,0:18:29.450
from lamps. I have a light in my laser[br]pointer with light from the sun. But we
0:18:29.450,0:18:35.380
need quite specific light sources to take[br]these snapshots of molecular motion. We've
0:18:35.380,0:18:37.970
already established that we want[br]ultrashort pulses because else we cannot
0:18:37.970,0:18:44.260
resolve femtosecond dynamics, but for the[br]proper kind of wavelength that we need I
0:18:44.260,0:18:47.980
would like to quickly remind you of the[br]electromagnetic spectrum that you've
0:18:47.980,0:18:54.090
probably seen at some point in high[br]school. So, so light, as you see here in
0:18:54.090,0:18:58.970
the bottom picture is an electromagnetic[br]wave that comes in different wavelengths.
0:18:58.970,0:19:05.440
They can be quite long as in the case of[br]radio waves to the very left. Then we have
0:19:05.440,0:19:08.470
the region of visible light shown here as[br]the rainbow that we can perceive with our
0:19:08.470,0:19:14.270
eyes. And then we have wavelengths that[br]are too short to see with our eyes. First,
0:19:14.270,0:19:18.880
UV radiation, that gives us a tan in the[br]summer if we leave our house and then we
0:19:18.880,0:19:25.400
have X-ray radiation, soft and hard X-ray[br]radiation that have atomic wavelength. So
0:19:25.400,0:19:30.570
the wavelength is really on the order of[br]the size of an atom. So what kind of
0:19:30.570,0:19:37.080
wavelength do we need to study ultra short[br]dynamics - ultra fast dynamics? We can
0:19:37.080,0:19:43.321
first think about what kind of wavelength[br]we need when we want to construct an ultra
0:19:43.321,0:19:49.600
short pulse. I've drawn here two pulses to[br]the left, a slightly longer pulse to the
0:19:49.600,0:19:53.980
right, a shorter pulse. And now if you[br]think about squeezing the left parts
0:19:53.980,0:19:58.610
together such that it becomes shorter and[br]shorter, you see visually that the
0:19:58.610,0:20:03.890
wavelength also needs to shrink. So we[br]need shorter wavelengths for the shorter
0:20:03.890,0:20:10.350
the pulse we want to make. So this will be[br]located somewhere here in this region of
0:20:10.350,0:20:15.450
the electromagnetic spectrum. And another[br]important thing that we need to keep in
0:20:15.450,0:20:21.250
mind is if we want to take pictures by[br]X-ray diffraction, we are limited, so we
0:20:21.250,0:20:27.429
can only resolve structures that are about[br]the same size as the wavelength we used to
0:20:27.429,0:20:31.919
take our diffraction image. So if we want[br]to take a picture of something with atomic
0:20:31.919,0:20:37.549
resolution, our wavelength needs to be of[br]atomic size as well. And this places us in
0:20:37.549,0:20:47.169
the region of X-Rays drawn here, that have[br]a wavelength of less than a nanometer. So
0:20:47.169,0:20:51.510
we can establish that we want small[br]wavelengths in general. We have two
0:20:51.510,0:20:55.840
additional requirements that would just[br]touch upon very briefly. First, we need
0:20:55.840,0:21:01.460
very brilliant pulses because the pulses[br]are so short, we need to have a lot of
0:21:01.460,0:21:06.760
light in the short pulse. You can think[br]about taking a picture in a dark room with
0:21:06.760,0:21:12.270
a bad camera. You won't see anything. So[br]we need very bright flashes of light.
0:21:12.270,0:21:16.159
Another requirement is we need coherent[br]laser light. So we cannot just use any
0:21:16.159,0:21:20.130
light, but it needs to have certain[br]properties like laser light.
0:21:20.130,0:21:25.110
Unfortunately, the lasers that you can buy[br]commercially do not operate in the region
0:21:25.110,0:21:29.110
of the electromagnetic spectrum that we[br]are interested in. So we need to come up
0:21:29.110,0:21:34.830
with something new. And I will show you[br]how we can generate ultra short pulses
0:21:34.830,0:21:39.380
both in the laboratory where we can[br]generate pulses that are very short and
0:21:39.380,0:21:46.650
extend up to maybe the soft X-ray region.[br]And another method to generate ultra short
0:21:46.650,0:21:53.380
pulses is at free electron laser sources,[br]where we can go really to the hard X-Ray
0:21:53.380,0:21:59.480
regime. But first I'd like to go to the[br]laboratory. So in the laboratory, it's
0:21:59.480,0:22:03.380
possible to generate an ultrashort pulse by[br]using a process that's called high
0:22:03.380,0:22:08.201
harmonic generation. In high harmonic[br]generation we start off of a high
0:22:08.201,0:22:13.470
intensity pulse, that's a red pulse coming[br]in from the left, which which is focused
0:22:13.470,0:22:19.350
in a gas cell. And from there, it[br]generates new frequencies of light. So the
0:22:19.350,0:22:24.770
light that comes out is no longer red, but[br]it's violet, blue. We cannot see it with
0:22:24.770,0:22:27.980
the naked eye. So that's an artist's[br]impression of how high harmonic generation
0:22:27.980,0:22:33.470
works. Before going into more detail about[br]why this method is so good at producing
0:22:33.470,0:22:38.770
ultra short pulses, I'd like to mention[br]that this is only possible because we have
0:22:38.770,0:22:44.120
the high intensity driving pulses, the red[br]laser pulses available. This goes back to
0:22:44.120,0:22:47.270
work by Donna Strickland and Gerard[br]Mourou, who were awarded the Nobel Prize
0:22:47.270,0:22:54.950
in the year 2018 in physics for this work[br]that has been done in the 80s. Now we're
0:22:54.950,0:22:59.690
coming to the only equation of his talk,[br]which is this equation that relates the
0:22:59.690,0:23:07.500
energy width and the time duration of a[br]ultra short pulse. By the law of fourier
0:23:07.500,0:23:13.150
limits we cannot have pulses that are very[br]short in time and at the same time very
0:23:13.150,0:23:17.700
narrow in energy. But we need to choose[br]one. So if we want to have policies that
0:23:17.700,0:23:23.640
are very short in time like the pulse that[br]I've shown here on the bottom, that is
0:23:23.640,0:23:26.669
actually only two hundred fifty[br]attoseconds long, so even shorter than a
0:23:26.669,0:23:33.059
femtosecond, then we need to have a very[br]broad width in energy. And this means
0:23:33.059,0:23:37.450
combining a lot of different colors inside[br]of this pulse. And this is what makes high
0:23:37.450,0:23:41.580
harmonic generation so efficient at[br]creating ultra short pulses, because the
0:23:41.580,0:23:47.419
spectrum that the colors that come out of[br]high harmonic generation are shown here
0:23:47.419,0:23:52.080
and they really span a long width. So we[br]get a lot of different colors with about
0:23:52.080,0:23:57.669
the same intensity. And you can think of[br]it like putting them all back together
0:23:57.669,0:24:04.990
into one attosecond pulse. That is very[br]short in time. This method has really made
0:24:04.990,0:24:08.950
a big breakthrough in the generation of[br]ultra short laser pulses we see here a
0:24:08.950,0:24:15.300
plot of a time duration of laser pulses[br]versus the year, and we see that since the
0:24:15.300,0:24:23.520
invention of the laser, here in the mid[br]60s, there was a first technological
0:24:23.520,0:24:28.920
progress and shorter and shorter pulses[br]could be generated. But then in the 80s,
0:24:28.920,0:24:34.399
there was a limit that had been reached of[br]about five femtoseconds, I believe. And we
0:24:34.399,0:24:39.710
could not really go farther than that and[br]only with high harmonic generation, that
0:24:39.710,0:24:45.419
sets in here shortly before the year 2000,[br]we were able to generate pulses that are
0:24:45.419,0:24:51.760
of a femtosecond duration. So that really[br]touch the timescale of molecular motion.
0:24:51.760,0:24:57.200
The current world record is a pulse, that[br]is only 43 attoseconds long, established
0:24:57.200,0:25:02.289
in the year 2017. So that's really the[br]timescale of electrons and we can do all
0:25:02.289,0:25:06.649
sorts of nice experiments with it where we[br]directly observe electronic motion in
0:25:06.649,0:25:12.470
atoms and molecules. This is all very[br]nice, but it has one limitation: We cannot
0:25:12.470,0:25:17.169
go to hard X-rays, at least not right now.[br]So high harmonic generation cannot produce
0:25:17.169,0:25:23.000
the kind of very short wavelengths that we[br]need in order to to do X-ray diffraction
0:25:23.000,0:25:29.429
experiments with atomic resolution. So if[br]we want to have ultra short pulses that
0:25:29.429,0:25:35.730
have X-Ray wavelengths, we need to build[br]right now very complex, very big machines,
0:25:35.730,0:25:43.080
the so-called free electon lasers. Now,[br]this would be a specific light source that
0:25:43.080,0:25:48.059
can produce ultra short pulses with X-ray[br]wavelengths in itself. The X-Ray
0:25:48.059,0:25:52.720
wavelengths is not so new. We know how to[br]take X-ray images for about one hundred
0:25:52.720,0:25:58.910
and thirty years and already in the 50s.[br]Rosalind Franklin, who is looking at a
0:25:58.910,0:26:05.110
microscope here, was able to take a[br]picture of DNA, an X-ray diffraction
0:26:05.110,0:26:11.880
pattern of a DNA double helix that was[br]successful in revealing the double helix
0:26:11.880,0:26:19.370
structure of our genetic code. But this is[br]not a time resolved measurement. So think
0:26:19.370,0:26:24.650
of it as you have a molecule that is in[br]crystalline form, so it's not moving
0:26:24.650,0:26:32.480
around and we can just take an X-ray image[br]of it, it's not going anywhere. But if we
0:26:32.480,0:26:36.860
want - if we want to take a picture of[br]something that is moving, we need to have
0:26:36.860,0:26:43.400
very short pulses. But we still need the[br]same number of what we call photons, light
0:26:43.400,0:26:48.890
particles. Or think of it as we need more[br]brilliant X-ray flashes of light than we
0:26:48.890,0:26:55.140
could obtain before. And there was very[br]nice technological development in the past
0:26:55.140,0:27:01.690
50 years or so, where we were able to go[br]from the X-ray tube to newer light sources
0:27:01.690,0:27:07.260
called Synchrotron, and today, free[br]electro lasers that always increase the
0:27:07.260,0:27:12.180
peak brilliance in an exponential way. So[br]we can take really brilliant, really
0:27:12.180,0:27:17.270
bright X-ray flashes right now. I cannot[br]go into the details of all of that, but I
0:27:17.270,0:27:21.350
found a very nice talk from two years ago,[br]but actually explains everything from
0:27:21.350,0:27:28.590
Synchrotron to FELs still available online[br]if you're interested in this work. And as
0:27:28.590,0:27:32.110
always, if something is failing scaling[br]exponentially, most of you will be
0:27:32.110,0:27:37.840
familiar with Moore's Law, that tells us[br]about the exponential scaling of
0:27:37.840,0:27:45.169
transistors. If something grows this fast,[br]it really opens up a new series of
0:27:45.169,0:27:49.299
experiments of new technological[br]applications that no one has thought of
0:27:49.299,0:27:55.600
before. And the same is true with free[br]electron lasers. So I'm going to focus
0:27:55.600,0:28:00.450
just on the most brilliant light sources[br]for X-rays. Right now, the free electron
0:28:00.450,0:28:06.230
lasers that are at the top right here of[br]this graph have been around for maybe 10
0:28:06.230,0:28:13.220
years or so. I cannot go into a lot of[br]detail on how to generate ultrashort
0:28:13.220,0:28:18.220
pulses with X-Rays. So I'd like to[br]give you just a very broad picture of how
0:28:18.220,0:28:23.909
this works. First, we need a bunch of[br]electrons, that is accelerated to
0:28:23.909,0:28:29.640
relativistic speed. This sounds very easy,[br]but is actually part of a two kilometer
0:28:29.640,0:28:35.490
long accelerator, that we have to build[br]and maintain. Now we have this bunch here
0:28:35.490,0:28:41.230
of electrons shown in red and it's really[br]fast and now we can bring it into
0:28:41.230,0:28:46.519
something that is called an undulator.[br]That's a series of alternating magnets,
0:28:46.519,0:28:52.270
shown here in green on blue for the[br]alternating magnets. And you may remember,
0:28:52.270,0:28:57.100
that when we put an electron, that is as a[br]charged particle, into a magnetic field,
0:28:57.100,0:29:02.820
the Lorence force will drive it away. And[br]if you have alternating magnets, then the
0:29:02.820,0:29:08.890
electron will go on a sort of wiggly path[br]in this undulator. And the electron is a
0:29:08.890,0:29:13.890
charged particle as it is wiggling around[br]wherever it turns around, it will emit
0:29:13.890,0:29:18.309
radiation, that happens to be in the X-ray[br]region of the electromagnetic spectrum,
0:29:18.309,0:29:23.260
which is exactly what we want. We can[br]watch this little movie here to see a
0:29:23.260,0:29:28.800
better picture. So this is the undulating[br]seeing from the side. We now go inside of
0:29:28.800,0:29:35.880
the undulator. We have a series of[br]alternating magnets. Now the electron
0:29:35.880,0:29:42.430
bunch shows up and you see the wiggly[br]motion as it passes the different magnets.
0:29:42.430,0:29:48.390
And you see the bright X-Ray flash that is[br]formed and gets stronger and stronger as
0:29:48.390,0:29:54.779
the electron bunch passes the undulator. So[br]we need several of these magnet pairs to
0:29:54.779,0:30:00.130
in the end, get the very bright X-Ray[br]flash. And at the end of the undulator we
0:30:00.130,0:30:06.240
dump the electron, we don't really need[br]this electron bunch anymore and continue
0:30:06.240,0:30:13.830
with a very bright X-Ray flash. This whole[br]process is a bit stochastic in nature, but
0:30:13.830,0:30:18.890
it's amplifying itself in because of the[br]undulator. This is why the longer the
0:30:18.890,0:30:29.020
undulator is, the more bright X-Ray[br]flashes we can generate. This whole thing
0:30:29.020,0:30:33.149
is kind of complicated to build, it's a[br]very complex machine. So right now there
0:30:33.149,0:30:37.740
are only very few free electron lasers in[br]the world. First one in California called
0:30:37.740,0:30:43.850
LCLS 1, currently being upgraded to LCLS[br]2. There are several in Europe. There's
0:30:43.850,0:30:49.330
one in Switzerland, in Italy and Hamburg.[br]So there's a Flash that does not operate
0:30:49.330,0:30:54.559
in the hot X-ray regime, but was kind of[br]first free electron laser. That's the most
0:30:54.559,0:30:58.919
recent addition to the free electron laser[br]zoo. It's the European XFEL also located
0:30:58.919,0:31:04.399
in Hamburg. And then we have some of these[br]light sources in Asia, in Korea, South
0:31:04.399,0:31:10.730
Korea, Japan, and one currently under[br]construction in Shanghai. I'd like to show
0:31:10.730,0:31:15.740
you a bit more details about the European[br]X-ray free electron laser, because it's
0:31:15.740,0:31:23.980
closest to us, and at least closest to[br]where I work. So the European XFEL is a
0:31:23.980,0:31:30.049
three point four kilometer long machine[br]that is funded by in total 12 countries,
0:31:30.049,0:31:36.350
So Germany and Russia paying the most and[br]then the other 10 countries also providing
0:31:36.350,0:31:41.130
to the construction and maintenance costs.[br]This machine starts at the DESY campus,
0:31:41.130,0:31:47.340
but as shown here to the right of the[br]picture. And then we have first an
0:31:47.340,0:31:51.580
accelerator line for the electrons that[br]it's already one point seven kilometers
0:31:51.580,0:31:58.450
long and where we add electrons reach[br]their relativistic speed. Then the
0:31:58.450,0:32:04.600
undulate comes in, so the range of magnets[br]where we X-Ray flashes are produced. The x
0:32:04.600,0:32:09.330
X-Ray flashes then cross the border to[br]Schleswig-Holstein, laughter shown here, on the
0:32:09.330,0:32:16.450
other side in a new federal state. They[br]reach the experimental hall. We have in
0:32:16.450,0:32:21.049
total six experimental end stations at the[br]European XFEL that provide different
0:32:21.049,0:32:24.419
instrumentation, depending on which kind[br]of system you want to study, you need
0:32:24.419,0:32:30.960
slightly different instruments. And it's[br]not only for taking molecular movies, but
0:32:30.960,0:32:36.010
the XFEL is used, among others, for[br]material science, for the imaging of bio
0:32:36.010,0:32:40.950
molecules, for femtosecond chemistry, all[br]sorts of things. So really wide range of
0:32:40.950,0:32:46.580
applications. It's right now the the[br]fastest such light source can take twenty
0:32:46.580,0:32:51.580
seven thousand flashes per second, which[br]is great because every flash is one
0:32:51.580,0:32:56.110
picture. So if we want to take a lot of[br]snapshots, if you want to generate a lot
0:32:56.110,0:33:01.179
of data in a short time, it's great to[br]have as many flashes per second as
0:33:01.179,0:33:08.720
possible. And as you can imagine, it's[br]kind of expensive since there are so few
0:33:08.720,0:33:15.450
free electron lasers in the world to take[br]measurements there. The complete price tag
0:33:15.450,0:33:19.919
for constructing this machine, it took[br]eight years and cost one point two billion
0:33:19.919,0:33:25.580
euros, which may seem a lot, but it's the[br]same amount that we spend on concert halls
0:33:25.580,0:33:39.029
in Hamburg. loud laughter applause So kind of comparable. Now,[br]when you factor in maintenance and so on,
0:33:39.029,0:33:45.639
I think a minute of X-Ray beam at such an[br]XFEL cost several thousands of tens of
0:33:45.639,0:33:51.570
thousands of euros in the end. So getting[br]measurement time is complicated and there
0:33:51.570,0:33:56.710
are committees that select the most[br]fruitful approaches and so on. So in order
0:33:56.710,0:34:04.000
to not to waste or do taxpayers money.[br]With this, I'd like to make a small
0:34:04.000,0:34:08.020
comparison of the light sources that I've[br]introduced now. So I introduced the
0:34:08.020,0:34:12.810
laboratory light sources and the XFEL[br]light source. In general, in the
0:34:12.810,0:34:17.600
laboratory we can generate very short[br]pulses of less than 100 attoseconds by now
0:34:17.600,0:34:22.980
and in the XFEL we are limited to[br]something about 10 femtoseconds right now.
0:34:22.980,0:34:29.630
In terms of brilliance the XFELs can go to[br]much more bright pulses, simply because
0:34:29.630,0:34:32.960
they are bigger machines and high harmonic[br]generation in itself is a kind of
0:34:32.960,0:34:38.870
inefficient process. In terms of[br]wavelength X-Ray free electron lasers
0:34:38.870,0:34:42.620
enable us to reach these very short[br]wavelengths with X-Rays, that we need to
0:34:42.620,0:34:48.290
get atomic resolution of defractive[br]images. In the laboratory we are a bit
0:34:48.290,0:34:54.850
more limited to maybe the soft X-ray[br]region. There's another important thing to
0:34:54.850,0:34:59.890
keep in mind when we do experiments,[br]that's the control of pulse parameters. So
0:34:59.890,0:35:03.040
is every pulse that comes out of my[br]machine the same as the one that came out
0:35:03.040,0:35:08.520
of my machine before. And since the XFEL[br]produces pulses by what is in the end, a
0:35:08.520,0:35:13.630
stochastic process, that's not really the[br]case. So the control of possible
0:35:13.630,0:35:20.400
parameters is not really given. This is[br]much better in the laboratory. And in
0:35:20.400,0:35:23.280
terms of cost and availability, it would[br]of course, be nice if we could do more
0:35:23.280,0:35:29.620
experiments in the lab. Then at the XFEL[br]simply because we XFEL ls so expensive to
0:35:29.620,0:35:35.730
build and maintain and we have so few of[br]them in the world. And you can see this
0:35:35.730,0:35:41.840
tunnel here. It stretches for two[br]kilometers or so, all packed with very
0:35:41.840,0:35:53.260
expensive equipment. So I'd like to show[br]you a brief example of what we can learn
0:35:53.260,0:35:58.500
in ultrafast science. So this is a[br]theoretical work that we did in our group.
0:35:58.500,0:36:03.720
So no experimental data, but still nice to[br]see. This is concerned with an organic
0:36:03.720,0:36:09.730
solar cell. So we all know solar cells.[br]They convert sunlight to electric energy
0:36:09.730,0:36:14.480
that we can use in our devices. The nice[br]thing about organic solar cells is that
0:36:14.480,0:36:20.900
they are foldable, very lightweight, and[br]we can produce them cheaply. The way that
0:36:20.900,0:36:25.630
such a solar cell works is we have light[br]shining in and at the bottom of the solar
0:36:25.630,0:36:29.410
cell there sits an electrode that collects[br]all the charges and creates an electric
0:36:29.410,0:36:33.570
current. Now light creates a charge that[br]somehow needs to travel down there to this
0:36:33.570,0:36:42.000
electrode and in fact, many of these[br]charges. So the important thing where we
0:36:42.000,0:36:46.640
build such an organic solar cell is that[br]we need a way to efficiently transport
0:36:46.640,0:36:55.240
these charges. And we can do so by putting[br]polymers inside. A polymer is just a
0:36:55.240,0:36:59.670
molecule that is made up of two different[br]or two or more different smaller
0:36:59.670,0:37:05.100
molecules. And one such polymer, which[br]should be very efficient at transporting
0:37:05.100,0:37:10.170
these charges is BT-1T, that is shown here[br]of a name is not so important, it's an
0:37:10.170,0:37:15.080
abbreviation. Because in BT-1T when we[br]create a charge at one end of a molecule
0:37:15.080,0:37:20.180
here at the top, it travels very quickly[br]to the other side of a molecule and you
0:37:20.180,0:37:26.880
can imagine stacking several of these[br]BT-1T or especially of the Ts together,
0:37:26.880,0:37:31.170
putting it in this material. And then we[br]have a very efficient flow of energy in
0:37:31.170,0:37:41.880
our organic solar cell. So what we did was[br]we calculated the ultrafast charge
0:37:41.880,0:37:48.161
migration in BT-1T, shown here to the[br]right. The pink thing is the charge
0:37:48.161,0:37:53.570
density that was created by an initial[br]ionization of the molecule. And now I show
0:37:53.570,0:37:58.110
you the movie, how this charge is moving[br]around in a molecule so you can see
0:37:58.110,0:38:02.820
individual atoms moving, the whole[br]molecules vibrating a bit. And the charge,
0:38:02.820,0:38:10.570
if you look closely, is locating on the[br]right half of a molecule within about 250
0:38:10.570,0:38:16.780
femtoseconds. Now, we cannot observe this[br]charge migration directly by looking at
0:38:16.780,0:38:21.290
this pink charge density that I've drawn[br]here, because it's at least for us, not
0:38:21.290,0:38:26.151
experimentally observable directly. So we[br]need an indirect measurement, an X-Ray
0:38:26.151,0:38:30.050
absorption spectroscopy that I showed you[br]in the beginning could be such a
0:38:30.050,0:38:35.310
measurement. Because in the X-Ray[br]absorption spectrum of BT-1T that I've
0:38:35.310,0:38:41.030
shown here in the bottom left, we see[br]distinct peaks depending on where the
0:38:41.030,0:38:47.070
charge is located. Initially the charge is[br]located at the top sulfur atom here and
0:38:47.070,0:38:53.780
this molecule and we will see a peek at[br]this color. Once the charge moves away to
0:38:53.780,0:38:58.060
the bottom of a molecule to the other[br]half, we will see a peak at the place
0:38:58.060,0:39:02.680
where nothing is right now because the[br]charge is not there. But if I start this
0:39:02.680,0:39:09.600
movie, we will again see very fast charge[br]transfer. So within about two hundred
0:39:09.600,0:39:14.050
femtoseconds, the charge goes from one end[br]to the molecule to the other end of a
0:39:14.050,0:39:19.470
molecule. And it would be really nice to[br]see this in action in the future XFEL
0:39:19.470,0:39:25.720
experiment. But the process is very long.[br]You need to apply for time at an XFEL. You
0:39:25.720,0:39:29.850
need to evaluate all the data. So maybe a[br]couple of years from now we will have the
0:39:29.850,0:39:37.730
data available. Right now we are stuck[br]with this movie, that we calculated. Now,
0:39:37.730,0:39:43.590
towards the end of my talk, I'd like to go[br]beyond the molecular movie. So I've shown
0:39:43.590,0:39:47.860
you now how to generate the light pulses[br]and an example of what we can study with
0:39:47.860,0:39:53.540
these light pulses. But this is not all we[br]can do: So when you think of a chemical
0:39:53.540,0:39:58.420
reaction, you might remember high school[br]chemistry or something like this, which is
0:39:58.420,0:40:03.460
always foaming and exploding and nobody[br]really knows what is going on. So a
0:40:03.460,0:40:08.480
chemical reaction quite naturally involves[br]molecular dynamics, for example, the
0:40:08.480,0:40:13.180
decomposition of a molecule to go from[br]here, from the left side to the right
0:40:13.180,0:40:18.180
side, the molecules will somehow need to[br]rearrange so all the atoms will have moved
0:40:18.180,0:40:24.340
quite a bit. We've seen already how we can[br]trigger these chemical reactions or these
0:40:24.340,0:40:29.770
molecular motion that was part of a[br]molecular movie. But it would be really
0:40:29.770,0:40:34.430
cool if we could control the reaction with[br]light. So the way to do this, it's not
0:40:34.430,0:40:38.920
currently something that is possible, but[br]maybe in the near future, would be to
0:40:38.920,0:40:44.440
implement a sort of optimisation feedback[br]loop. So we would record the fragments of
0:40:44.440,0:40:48.970
our reaction, send it to an optimization[br]routine that will also be quite
0:40:48.970,0:40:53.620
complicated and will need to take into[br]account the whole theory of how light and
0:40:53.620,0:40:58.770
matter, interact and so on. And this[br]optimization routine would then generate a
0:40:58.770,0:41:03.800
new sequence of ultra short pulses and[br]with this feedback loop, it might be
0:41:03.800,0:41:10.100
possible to find the right pulses to[br]control chemical reactions, taking into
0:41:10.100,0:41:17.640
account the quantum nature of this motion[br]and so on. Right now this is not possible.
0:41:17.640,0:41:23.651
First, because the whole process of how we[br]can generate these ultra short pulses is
0:41:23.651,0:41:28.760
not so well controlled that we could[br]actually implement it in such a loop. And
0:41:28.760,0:41:33.000
also the step optimization routine is more[br]complex than it looks like here in this
0:41:33.000,0:41:39.490
picture. So this is something that people[br]are working on at the moment, but this
0:41:39.490,0:41:44.300
would be something like the ultra fast[br]wishlist for next Christmas, not this
0:41:44.300,0:41:49.710
Christmas. So we've succeeded in taking a[br]molecular movie, but we would also like to
0:41:49.710,0:41:55.270
be able to direct a molecular movie. So to[br]go beyond just watching nature, but
0:41:55.270,0:42:01.460
controlling nature because this is what[br]humans like to best, laughing fortunately or
0:42:01.460,0:42:06.230
unfortunately, it depends. So I'd like to[br]just show you that this is really an ultra
0:42:06.230,0:42:12.220
fast developing field. There's lots of new[br]research papers every day, every week
0:42:12.220,0:42:18.070
coming in, studying all sorts of systems.[br]When you just take a quick and dirty
0:42:18.070,0:42:22.820
metric of how important ultrafast science[br]is this is the number of articles per year
0:42:22.820,0:42:28.500
that mentioned ultrafast in Google[br]Scholar, it's exponentially growing. At
0:42:28.500,0:42:30.780
the same time, the number of total[br]publications in Google Scholar is more or
0:42:30.780,0:42:34.990
less constant, so the blue line here[br]outgrows the green line considerably since
0:42:34.990,0:42:45.070
about ten years. So what remains to be[br]done? We've seen that we have light
0:42:45.070,0:42:50.020
sources available to generate ultra short[br]pulses, but as always, when you have
0:42:50.020,0:42:55.540
better machines, bigger machines, you can[br]take more fancy experiments. So it would
0:42:55.540,0:43:00.580
be really nice to develop both lab based[br]sources and free electron laser sources so
0:43:00.580,0:43:06.360
that we can take more, more interesting,[br]more complex experiments. Another
0:43:06.360,0:43:10.060
important challenge, that's what people in[br]my research group where I work are working
0:43:10.060,0:43:16.750
on is to improve theoretical calculations[br]because I did not go into a lot of detail
0:43:16.750,0:43:21.730
on how to calculate these things, but it's[br]essentially quantum mechanics and quantum
0:43:21.730,0:43:26.530
mechanics skales very unfavorably. So[br]going from a very small molecule like the
0:43:26.530,0:43:32.490
glycene molecule here to something like a[br]protein is not doable. Simply, it cannot
0:43:32.490,0:43:38.100
compute this with quantum mechanics. So we[br]need all sorts of new methodology to -
0:43:38.100,0:43:45.100
Yeah - to better describe larger systems.[br]We would in general like to study not only
0:43:45.100,0:43:49.410
small molecules and not only take movies[br]of small molecules, but really study large
0:43:49.410,0:43:55.710
systems like this is the FMO complex, that[br]is a central in photosynthesis or solid
0:43:55.710,0:44:01.410
states that are here shown in this crystal[br]structure simply because this is more
0:44:01.410,0:44:07.790
interesting for biological, chemical[br]applications. And finally, as I've shown
0:44:07.790,0:44:13.460
you, it would be cool to directly control[br]chemical reactions with light. So to find
0:44:13.460,0:44:20.810
a way how to replace this mess with a[br]clean light pulse. With this, I'm at the
0:44:20.810,0:44:26.240
end. I'd like to quickly summarize[br]femtodynamics, really fundamental in
0:44:26.240,0:44:31.500
biology, chemistry and physics. So more or[br]less, the origin of life is on this
0:44:31.500,0:44:36.840
timescale. We can take molecular movies[br]with ultrashort laser pulses and we can
0:44:36.840,0:44:41.650
generate these pulses in the laboratory or[br]add free electron lasers with different
0:44:41.650,0:44:46.820
characteristics. And we would like to not[br]only understand these ultra fast
0:44:46.820,0:44:51.920
phenomena, but we would also like to be[br]able to control them in the future. With
0:44:51.920,0:44:54.160
this, I'd like to thank you for your[br]attention and thank the supporting
0:44:54.160,0:45:04.570
institutions here that funded my PhD work.
0:45:04.570,0:45:10.820
applause
0:45:10.820,0:45:17.380
Herald: Well, that was an interesting[br]talk. I enjoyed it very much. I guess this
0:45:17.380,0:45:23.450
will spark some questions. If you want to[br]ask Caroline a question, please line up
0:45:23.450,0:45:28.900
behind the microphones. We have three in[br]the isles between the seats if you want to
0:45:28.900,0:45:36.070
leave, please do so in the door here in[br]the front. And until we get questions from
0:45:36.070,0:45:39.570
the audience, do we have questions from[br]the Internet?
0:45:39.570,0:45:45.311
Signal angel: Yes. Big fat random user is[br]curious about the design of the X-Ray
0:45:45.311,0:45:48.460
detector. Do you have any information on[br]that?
0:45:48.460,0:45:56.030
Caroline: That's also very complex. I'm[br]not a big expert in detectors. At this
0:45:56.030,0:45:58.460
point, I really recommend watching the[br]talk from two years ago, that explains a
0:45:58.460,0:46:05.140
lot more about the X-Ray detectors. So[br]what I know about the X-Ray detector is
0:46:05.140,0:46:09.990
that it's very complicated to process all[br]the data because when you have 27000
0:46:09.990,0:46:16.370
flashes of light, it produces, I think[br]terabytes of data within seconds and you
0:46:16.370,0:46:21.030
need to somehow be able to store them and[br]analyze them. So there is also a lot of
0:46:21.030,0:46:24.190
technology involved in the design of these[br]detectors.
0:46:24.190,0:46:30.060
Herald: Thank you. So the first question[br]from microphone 2 in the middle.
0:46:30.060,0:46:34.110
Microphone 2: So my question is.[br]Herald: Please go close to the microphone.
0:46:34.110,0:46:38.860
Microphone 2: My question is regarding the[br]synchronization of the detector units when
0:46:38.860,0:46:45.030
you're pointing to free electron laser so[br]you can achieve this in synchronization.
0:46:45.030,0:46:50.700
Caroline: This is also very complicated.[br]It's easier to do in the lab. So you're
0:46:50.700,0:46:54.800
talking about the synchronization of[br]essentially the first pulse and the second
0:46:54.800,0:47:00.540
pulse. Right. So in the lab, you typically[br]generate the second pulse from part of the
0:47:00.540,0:47:05.310
first pulse. So you have a very natural[br]alignment, at least in time of these two
0:47:05.310,0:47:10.190
pulses. The X-ray free electron lasers[br]have special timing tools that allow you
0:47:10.190,0:47:16.830
to find out how much is the time delay[br]between your two pulses. But it's true
0:47:16.830,0:47:21.520
that this is complicated to achieve and[br]this limits the experimental time
0:47:21.520,0:47:25.860
resolution to something that is even[br]larger than the time duration of the
0:47:25.860,0:47:30.540
pulses.[br]Herald: So now next question from
0:47:30.540,0:47:35.930
microphone number 3.[br]Microphone 3: Yes, i remember in the
0:47:35.930,0:47:42.810
beginning, you explained that your[br]measuring method usually destroys your
0:47:42.810,0:47:49.700
molecules. That's a bit of a contradiction[br]to your idea to control. laughing
0:47:49.700,0:47:59.090
Caroline: In principle, yes. But, so in[br]the case of control, we would like to use
0:47:59.090,0:48:04.650
a second pulse, that does not destroy the[br]molecule. But for example, at least
0:48:04.650,0:48:11.140
destroys it in a controlled way, for[br]example. loud laughter So there's a difference between
0:48:11.140,0:48:15.250
just blowing up your molecule and breaking[br]apart a certain part, but yet that we are
0:48:15.250,0:48:19.770
interested in. And that's what we would[br]like to do in the control case. So we
0:48:19.770,0:48:24.490
would like to be able to to control, for[br]example, the fragmentation of a molecule
0:48:24.490,0:48:30.230
such that we only get the important part[br]out and everything else just goes away.
0:48:30.230,0:48:34.430
Microphone3: Thank you.[br]Herald: So then another question for
0:48:34.430,0:48:39.240
microphone 2 in the middle.[br]Microphone 2: So thank you for the talk. I
0:48:39.240,0:48:44.470
was interested in how large structures or[br]molecules can you imagine with this lab
0:48:44.470,0:48:48.520
contributions and with this XFEL thing?[br]Caroline: Sorry. Can you repeat?
0:48:48.520,0:48:54.790
Microphone 2: So how large molecules can[br]you imagine in this laboratory with this
0:48:54.790,0:48:59.120
high harmonic measures?[br]Caroline: So how large is not really the
0:48:59.120,0:49:05.630
fundamental problem? People have taken[br]snapshots of viruses or bigger bio
0:49:05.630,0:49:11.870
molecules. If you want to - the problem is[br]rather how small can we get? So yeah, to
0:49:11.870,0:49:16.370
take pictures of a very small molecule.[br]Currently we cannot take a picture of an
0:49:16.370,0:49:21.780
individual small molecule, but what people[br]do is they create crystals of a small
0:49:21.780,0:49:25.260
molecule, sticking several of them[br]together and then taking images of this
0:49:25.260,0:49:30.371
whole crystal for single particles, I[br]think right now about the scale of a virus
0:49:30.371,0:49:34.180
nanometers.[br]Microphone 2: Thank you.
0:49:34.180,0:49:38.190
Herald: OK. Do we have another question[br]from the Internet?
0:49:38.190,0:49:43.740
Signal Angel: We have. So this is[br]concerning your permanent destruction of
0:49:43.740,0:49:49.450
forces, I guess. How do you isolate single[br]atoms and molecules for analysing between
0:49:49.450,0:49:55.860
the different exposures?[br]Caroline: Yes, excellent question. So
0:49:55.860,0:50:01.440
molecules can be made available in the gas[br]phase by - so if you have them in a solid
0:50:01.440,0:50:08.030
somewhere and you heat that up, they will[br]evaporate from that surface. This is how
0:50:08.030,0:50:11.760
you can get them in the gas phase. This,[br]of course, assumes that you have a
0:50:11.760,0:50:15.940
molecule, that is actually stable in the[br]gas space, which is not true for all
0:50:15.940,0:50:22.450
molecules. And then the, the hard thing is[br]to align all three things. So the pump
0:50:22.450,0:50:27.540
pulse, the probe pulse and the molecule[br]all need to be there at the same time.
0:50:27.540,0:50:32.600
There are people doing whole PhD theses on[br]how to design gas nozzles that can provide
0:50:32.600,0:50:37.670
this stream of molecules.[br]Signal Angel: So you basically really
0:50:37.670,0:50:41.190
having a stream coming from a nozzle?[br]Caroline: Yes.
0:50:41.190,0:50:43.300
Signal Angel: It's a very thin stream, I[br]guess.
0:50:43.300,0:50:47.620
Caroline: Yes.[br]Signal Angel: Then you're exposing it like
0:50:47.620,0:50:49.990
in a regular interval.[br]Caroline: And of course you try to hit as
0:50:49.990,0:50:56.180
many molecules as possible. So this is[br]especially important when you do pictures
0:50:56.180,0:50:59.760
of crystallized molecules because[br]crystallizing these molecules is a lot of
0:50:59.760,0:51:04.480
work. You don't want to waste like 99[br]percent that just fall away and you never
0:51:04.480,0:51:07.990
take snapshots of them.[br]Signal Angel: Thanks.
0:51:07.990,0:51:10.990
Herald: So another question from[br]microphone 3.
0:51:10.990,0:51:18.810
Microphone 3: How do you construct this[br]movie? I mean, for every pulse to have a
0:51:18.810,0:51:25.240
new molecule and for every molecule is[br]oriented differently in space and has
0:51:25.240,0:51:31.190
different oscillation modes. How do[br]correlate them? I mean, in the movie, I
0:51:31.190,0:51:35.100
mean, every molecule is different than the[br]previous one.
0:51:35.100,0:51:41.400
Caroline: Yes. Excellent question. That's,[br]So first, what people can do is align
0:51:41.400,0:51:48.430
molecules. So especially molecules that[br]are more or less linear. You can force
0:51:48.430,0:51:55.410
them to be oriented in a certain way. And[br]then there's also a bit of a secret in the
0:51:55.410,0:52:00.220
trigger pulse that first sets off this[br]motion. For example, if this trigger pulse
0:52:00.220,0:52:04.600
is a very strong proto ionization, then[br]this will kill off any sorts of
0:52:04.600,0:52:08.910
vibrational states that you have had[br]before in the molecule. So in this sense,
0:52:08.910,0:52:12.840
the trigger parts really defines a time[br]zero, that should be reproducible for any
0:52:12.840,0:52:17.950
molecule that shows up in the stream and[br]the rest is statistics.
0:52:17.950,0:52:23.580
Microphone 3: Thank you.[br]Herald: So there's another question on
0:52:23.580,0:52:27.070
microphone 3.[br]Microphone 3: Are there any pre pulses or
0:52:27.070,0:52:31.420
ghosts, You need to get rid of?[br]Caroline: Sorry. Again.
0:52:31.420,0:52:36.550
Microphone 3: You have to control pre[br]pulses or ghosts during this effect for
0:52:36.550,0:52:39.560
measurement.[br]Caroline: That I'm not really sure of,
0:52:39.560,0:52:42.090
since I'm not really conducting[br]experiments, but probably.
0:52:42.090,0:52:49.510
Herald: And another one from the middle,[br]from microphone 2 please.
0:52:49.510,0:52:55.430
Microphone 2: I suppose if you apply for[br]experimentation time at the XFEL laser,
0:52:55.430,0:53:02.000
you have to submit very detailed plans and[br]time lines and everything. And you will
0:53:02.000,0:53:07.950
get the time window for your experiment, I[br]guess. what's going to happen if you're
0:53:07.950,0:53:13.760
not completely finished within that time[br]window? Are they easy possibilities to
0:53:13.760,0:53:19.180
extend the time or are they do they just[br]say, well, you had your three weeks,
0:53:19.180,0:53:23.120
you're out apply in 2026?[br]Caroline: Yeah, I think it's a regular
0:53:23.120,0:53:26.930
case, that you're not finished with your[br]experiments by the time your beam time
0:53:26.930,0:53:31.870
ends. That's how it usually goes. It's[br]also unfortunatly not free weeks, but it's
0:53:31.870,0:53:38.531
rather like 60 hours delivered in five[br]shifts of twelve hours. So, yeah, you
0:53:38.531,0:53:43.250
write a very detailed proposal of what you[br]would like to do. Submit it to a panel of
0:53:43.250,0:53:50.620
experts, both scientists and technicians.[br]So they decide, is it interesting enough
0:53:50.620,0:53:54.980
from a scientific point of view and is it[br]feasible from a technical point of view?
0:53:54.980,0:54:00.320
And then once you are there, you more or[br]less set up your experiment and do as much
0:54:00.320,0:54:06.490
as you can. If you want to come back, you[br]need to submit an additional proposal. So,
0:54:06.490,0:54:10.590
yeah, I think most experimental groups try[br]to have several of these proposals running
0:54:10.590,0:54:15.490
at the same time, so that there is not a[br]two year delay between your data
0:54:15.490,0:54:21.070
acquisition. But yes. No possibility to[br]extend. It's booked already for the
0:54:21.070,0:54:27.890
complete next year. The schedule is fixed.[br]Herald: So I don't see any more people
0:54:27.890,0:54:33.060
queuing up. If you want to pose a[br]question, please do so now. In the
0:54:33.060,0:54:35.460
meantime, I would ask the signal angel if[br]there's another question from the
0:54:35.460,0:54:38.240
Internet.[br]Signal Angel: I have a question about the
0:54:38.240,0:54:44.650
dimensions of all those machines. The[br]undulator seems to be rather long and
0:54:44.650,0:54:48.910
contain a lot of magnets. Do you have an[br]idea how long it is and how many of those
0:54:48.910,0:54:55.221
electromagnets are in there?[br]Caroline: Yeah. Sorry, I didn't mention
0:54:55.221,0:54:57.221
it. It's about, I think one hundred and[br]seventy meters long in the case of the
0:54:57.221,0:55:03.390
European XFEL. I'm not sure about the[br]dimension of the individual magnets, but
0:55:03.390,0:55:09.100
it's probably also in the hundreds of[br]magnets, magnet pairs.
0:55:09.100,0:55:16.080
Herald: So is there more - excuse me,[br]there is a question on the microphone
0:55:16.080,0:55:20.350
number 3.[br]Microphone 3: Yeah. Hi. It's regarding the
0:55:20.350,0:55:22.350
harmonic light.[br]Herald: Please go closer to the
0:55:22.350,0:55:24.350
microphone.[br]Microphone 3: The harmonic light generator
0:55:24.350,0:55:26.870
that you were showing at the very[br]beginning, just before the one that won
0:55:26.870,0:55:32.700
the Nobel Prize. And can you also produce[br]light in the visible range? Or it has to
0:55:32.700,0:55:38.050
be in the visible range?[br]Caroline: The high harmonic generation? So
0:55:38.050,0:55:43.160
in the in the visible range, you cannot[br]create pulses that are so short that they
0:55:43.160,0:55:50.960
would be interesting for what I'm doing.[br]The pulse that comes in is already quite
0:55:50.960,0:55:54.791
short. So it's already femtoseconds long.[br]They just convert it into something that
0:55:54.791,0:56:01.850
is fractions of a femtosecond long. And[br]yeah. In the indivisible range that's kind
0:56:01.850,0:56:05.800
of a limit how short your pulse can be.[br]Microphone 3: So it is not a good
0:56:05.800,0:56:11.060
candidate for hyperspectral light source.[br]We need another kind of technique, I
0:56:11.060,0:56:16.360
guess.[br]Caroline: Well, I mean you are kind of
0:56:16.360,0:56:21.070
limited what short pulses you can generate[br]with which wavelength.
0:56:21.070,0:56:26.441
Microphone 3: Thank you.[br]Herald: So again, a question to the Signal
0:56:26.441,0:56:29.020
Angel. Are there more questions from the[br]internet?
0:56:29.020,0:56:34.590
Signal Angel: Yes I have another one about[br]the lifetime of the molecules in the beam?
0:56:34.590,0:56:39.800
How fast are they degrading or how fast[br]are they destructed?
0:56:39.800,0:56:44.290
Caroline: So probably the question is[br]about how fast they are destructed before
0:56:44.290,0:56:53.420
- so either before our pulses hit the[br]molecule the molecules should be stable
0:56:53.420,0:56:57.330
enough to survive in the gas phase from[br]the point where they are evaporated until
0:56:57.330,0:57:01.370
the point where the pump and the probe[br]pulse come together, because otherwise it
0:57:01.370,0:57:07.560
doesn't make sense to study this molecule[br]in the gas phase. When the probe pulse
0:57:07.560,0:57:12.690
hits and it flows apart, I guess pico[br]seconds until the whole molecules ...
0:57:12.690,0:57:21.780
Microphone 3: Like instantaneous.[br]Herald: So I don't see any more questions
0:57:21.780,0:57:26.040
on the microphones and we have a few[br]minutes left. So if there are more
0:57:26.040,0:57:30.030
questions from the Internet, we can take[br]maybe one or two more.
0:57:30.030,0:57:42.560
Signal Angel: Give me a second.[br]Herald: For people leaving already, please
0:57:42.560,0:57:46.760
look if you have taken trash and bottles[br]with you.
0:57:46.760,0:57:52.390
Signal Angel: So this one very, very[br]technical question. How do you compensate
0:57:52.390,0:57:58.210
the electronic signal that the electronic[br]signal reaction is probably slower than x
0:57:58.210,0:58:05.240
ray or light or spectrum changes at one[br]moment or at one particular moment, that
0:58:05.240,0:58:10.170
was interesting to analyze. I do not[br]understand the question, though.
0:58:10.170,0:58:13.240
Caroline: I think I understand the[br]question, but I don't have the answer
0:58:13.240,0:58:16.860
because again, I'm a - that's the problem[br]of speaking to a technical audience, you
0:58:16.860,0:58:23.710
get a lot of these very technical[br]question. Yeah. The data analysis is not
0:58:23.710,0:58:32.810
instantaneous. So the data is transported[br]somewhere safe in my imagination. And then
0:58:32.810,0:58:37.180
taken from there. So this data analysis[br]does not have to take place on the same
0:58:37.180,0:58:41.330
timescale as the data acquisition, which I[br]guess is also because of the problem that
0:58:41.330,0:58:47.530
was mentioned in the question.[br]Herald: I might interrupt here. Maybe it's
0:58:47.530,0:58:55.680
also about the signal transmission, like[br]the signal rising of the signal of the
0:58:55.680,0:59:01.900
electrical signal transmissions. Because[br]this would probably require bandwidths of
0:59:01.900,0:59:06.680
several megahertz, gigahertz, I don't[br]know, to transport these very fast
0:59:06.680,0:59:09.680
results.[br]Caroline: Yeah. I think that's also a
0:59:09.680,0:59:15.130
problem of constructing the right[br]detector. That has been solved apparently
0:59:15.130,0:59:20.690
because they can take these images. laughter[br]Herald: And on the other hand, we have 10
0:59:20.690,0:59:28.760
gigabit either nets. So we get faster and[br]faster electronics. More questions from
0:59:28.760,0:59:39.921
the Internet? Does not look like it, also[br]the time is running out. So let's thank
0:59:39.921,0:59:42.760
Caroline for her marvelous talk. Applause, final music
0:59:42.760,1:00:13.000
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