is excited about photography or videography yeah the title of the talk kind of gives it away okay we bet we are waiting for the last people to come in and take a seat last time raise your hands if you have a free seat next to you everyone of you coming in look for a raised end take your seat and then we will start yeah very good okay looks like the doors are finally closed okay so the next talk on the second day is about ultra fast imaging so many of you have done videography or photography have thought about exposure time how fast you can do your photography and some of you might have played with lasers and have built blinky stuff with it or have done scientific experiments and Carolina will now show us what it happens if we take those two combine them and take it to the extreme Carolina is working at Daisy since four years she has done her PhD and is now working in a group for theoretical fast model modeling of inner workings of molecules and atoms she is doing computational work and working together with experimentalists to verify their observations and now she's presenting the inner mechanics of what she is doing and how we can actually maybe photograph molecules by their forming applause yeah thank you very much for the introduction and thank you very much for having me here I'm excited to see this room so full so I'm going to speak today about an ultra short history of ultra fast imaging it's a really broad topic and I'm just gonna present some highlights some background before I start I'd like to give you a few more few more words about myself as we've already heard I work at Daisy this is the Daisy campus you see here and in the Center for free electron laser science circuit in orange that's where I did my PhD so this whole campus is located in Hamburg this is probably also a familiar place to many of you and now this year we are in Leipzig a bit further away for the 36 Congress so I'd like to start with a very broad question what is the goal of ultra fast imaging and we've heard already that ultra fast imaging is related to photography now as many of you know when you take a picture with a quite long exposure time you see just a blurry image for example in this picture of a bowl of water we can hardly see anything it looks a bit foggy but if we choose the correct exposure time which in this case is a hundred times shorter in the right picture then in the left picture then we see a clear image and we can see dynamics unfold so we have here a drop of water that is bouncing back from the bowl and also some ripples that are forming on the surface of this bowl this is only visible because we chose the right exposure time and this is to me really the key of being successful in ultra fast imaging to take a clear picture of an object that is moving but it's not enough to say take just a picture so now imagine you're a sports reporter you get these two pictures and you're supposed to write up what happened so it complicated so the top pictures the start the bottom pictures the end just from these two pictures it's hard to see but if we see the full picture we can see very complex dynamics unfold there are particles accelerating at high velocity coming in from the back and even particles we did not see in the first picture at all somehow are very relevant to our motion and not only skiing races are very dynamic but most processes in nature are also not static this is true for everything we see around ourselves but it's especially true for everything that is quite small in the microcosm and in general we can gain a lot more insight from time-resolved images so from ultra short movies I'd like to show you the very first ultra fast movie that was ever taken or maybe even the first movie that was taken at all this guy Edward Muybridge lived in the 19th century and very shortly after the invention of a photographer photography method he tried to answer the question does a galloping horse ever lift all of its feet off the ground while it's running to us it may seem like not so important question but in the 19th century the horse was the main method of transportation and horse races were very popular so there was a lot of interest in studying the dynamics of a horse and this process is too fast to see with a naked eye but Muybridge implemented a stop motion technique where the horse as it is running cuts some wires that then trigger photo photographs and with this he was able to take these 12 photographs of the horse in motion that was published under this title in Stanford in the 19th century and we see very clearly in the top row third picture and maybe also second picture that indeed the horse lifts all of its legs off the ground which was a new insight at that time and when we stitch all of these snapshots together we have an ultra fast movie of the horse galloping which might be seen as the first movie that was ever made in the history of mankind now when I say ultra fast today I'm no longer thinking about horses but about smaller things and faster things but let's go there very gently so the timescale that we are all familiar with that we can see with the naked eye is something of the order of seconds so for example the acceleration of this cheetah we can see with the naked eye now if we zoom in on this motion we see that there are muscles inside of the animal that are contracting as it is running and this muscle contraction takes place within milliseconds so that's a part of a thousand in one second but we can go even smaller than that to the microsecond so proteins inside of the muscles are in any biological matter fold and unfold on a timescale of microseconds that's already a part in a million of a second now going even smaller to nanoseconds there's certain dynamics that takes place within these proteins for example how they dissolve in water but the timescale that I'm interested in today is the femtosecond it's even faster than that it's the timescale where individual atoms move in molecules as shown in this animation now a femtosecond is very short it's a part in a million of a billion of a second or as the physicists like to call it 10 to the minus 15 seconds because that's easier to spell we can to us we can go even faster than that the timescale of electronic motion in molecules would be the attosecond I'm just mentioning it here because we don't stop at molecules but nature is even faster than that but for the purpose of this talk I will mainly focus on processes that takes place within the femtosecond so within 10 to the minus 15 seconds now this timescale is something that is not really related to what we think about in everyday life but there are certain processes in chemistry biology and physics that are really fundamental and that start at this timescale just to give you an idea how short a femtosecond is the width of a human hair is about a hundred micrometer is shown here in an electron microscopic picture and for light at the speed of light it takes only 30 femtoseconds to cross the hair so that's how fast a femtosecond is and even of all this timescale is so short there are many important processes that start here I'd like to mention just two of them the first one is vision in our eyes and our retina there sits a molecule called rhodopsin that is shown here to the left and when light hits rhodopsin it starts to isomerize which is a fancy word for saying it changes its shape and this transmits in the end electrical impulses to our brain which enables us to see and this very first step of vision takes only 200 femtoseconds to complete but without it vision would not be possible another very fast process that is fundamental in nature is photosynthesis where plants take light and co2 and convert it to other things among them oxygen and the very first excitation where light hits the plant and it starts to to make all this energy available that also takes less than a hundred femtoseconds to complete so really the fundamental questions of life lie at this timescale and I'd like to just mention that all of these processes are not only very fast but they also take place in very small objects that are of the size of few atoms to nanometers which makes it also hard to observe because we cannot see them with a naked eye or with standard microscopes now we've seen already that it's important to choose the right exposure time to get a clear image of something that is moving but the kind of method that we need for taking such a photograph of something that is moving depends a lot on the timescale so for stuff that is moving within seconds of fractions of a second we can see that with a naked eye we can use cameras to resolve faster motion pretty much like Muybridge did with the very first camera today of course we can go much faster to maybe few microseconds with very fancy cameras called optoelectronic street cameras I won't go into detail here we can go down to pico seconds so we are already very close to the motion of molecules but we are not quite there yet the timescale that we want to investigate is a femtosecond so really a timescale of molecular motion and electronics are not fast enough to reach this timescale so we need something new and fortunately we can create light pulses that serve us to say flashes that take snapshots of our moving molecules with femtosecond time resolution and light pulses can be made so short so in the following I'm going to show you a bit more detail on how we can use these ultra short light pulses to take snapshots of moving molecules the first method that I would like to briefly show you is x-ray diffraction where we have an ultra short pulse and x-ray pulse coming in it's a sample shown here in as a red bubbles that's essentially a molecule that we just place in the beam and it produces a so-called diffraction pattern that we can then record on a screen now the whole process is quite complicated so I'd like to just sketch the very basics of it we see here x-ray radiation hitting a crystalline sample here to the left and the sample is excited starts to radiate x-rays back and on the right we can see the x-rays leaving the sample again they will interfere and we can record this pattern on the screen so this is what we see here in this visualization to the right with this we can feed a reconstruction algorithm that allows us to transform back our diffraction pattern that we've seen here for in this case a biomolecule we can reconstruct from that the image as it was in real space so this is some protein I believe x-ray diffraction is very nice for resolving small structures with atomic detail another method how we can take snapshots using ultra short pulses but I would like to briefly introduce is absorption spectroscopy now you may know that light contains several colors for example you've surely have held a prism in hand and the prism can break white light up into all the colors of a rainbow that we can see with the eye now we can do the same with x-ray pulses then we cannot see the colors anymore so just let's just stick with a prism here when we place a molecule in front of all these colors the molecule will block certain colors that's quantum mechanics you just have to believe it or or learn about it in long studies so the molecule is placed in front of all these colors and to the right the absorption spectrum is recorded and the the parts of the spectrum that are very bright correspond to the colors that have been blocked by the molecule and this is a very nice technique to investigate ultra short dynamics because where these lines are located is characteristic of the chemical elements that we find in the molecule for example if we use x-ray radiation for this specific molecule that I've shown here glycine it's not so important which molecule it is we have three different atoms in this molecule that are important carbon nitrogen and oxygen and they absorb at very different colors so we can keep them apart when we take the spectrum but not only that we can take the spectrum at a later time when the molecule has moved around a bit and we will see that the colors the position of the lines have changed a tiny bit so it's really not much and I exaggerated it already in this visualization quite a bit but with experimental methods we can resolve this and this allows us to then trace back to how the molecule was moving in between when we took these two snapshots there are many more methods where you can use to take ultra-fast images so we call them probe signals because we probe the ultra-fast motion of a molecule with such an ultra-short pulse for example we can record photoelectrons or we can record fragments of a molecule and many more but I won't go into further detail here because this is a non-exhaustive list of methods that we can use I'd rather like to show you how we can take molecular movies so how we can combine all these ultra-short pulses to in the end film a molecule in action now we've already seen in the movie of the horse that we need to stitch several snapshots together and then we have a full picture full motion of a molecule so we just like to do the same but 10 to the 15 times faster should not be too difficult right so we use our ultra-short pulse first ultra-short pulse that we use is a trigger pulse that sets off the motion in the molecule this defines as a certain time zero in our experiment and makes it sort of repeatable because we always start the same kind of motion by giving it a small hit and now it's just moving around so we wait for a certain time a time delay and then come in with a probe pulse the probe pulse takes a snapshot of a molecule this goes to some detector goes to a kind of complicated reconstruction method that we just execute from our screen and with this we reconstruct a snapshot of a molecule but this is only one snapshot and we want a whole movie so we need to repeat this process over and over again by shining in more and more probes and this will create more and more snapshots of a molecule and in the end we could stitch all of these together and we would arrive at the same image that you see in the in the middle where the molecule is happily moving around there's one little problem the probe parts typically destroys the molecule this is very different this is very different from taking pictures of a horse the horse normally survives so the probe parts destroys the molecule it just goes away so for each of these snapshots we need to use a new molecule so we typically have a stream of samples that is falling from the top to the bottom in our experiment and then we have to carefully align two pulses a trigger pulse and a probe pulse that come together and take a snapshot of this molecule and of course we have to find a method on how to make identical molecules available in yeah you see there's a lot of complications with doing these experiments that I'm completely leaving out here so now we want to take a molecular movie and we know that we want to have ultra short pulses to do so but I didn't tell you yet what kind of light source we need so there are many light sources all around us we have here light from lamps I have a light in my laser pointer we have light from the Sun but we need quite quite specific light sources to take these snapshots of molecular motion we've already established that we want ultra short pulses because else we cannot resolve femtosecond dynamics but for the for the kind of wavelength that we need I would like to quickly remind you of the electromagnetic spectrum spectrum that you've probably seen at some point in high school or so so light as you see here in the bottom picture is an electromagnetic wave that comes in different wavelengths they can be quite long as in the case of radio waves to the very left then we have the region of visible light shown here as the rainbow that we can perceive with our eyes and then we have wavelengths that are too short to see with our eyes first UV radiation that gives us a 10 in the summer if we leave our house and then we have x-ray radiation soft and hard x-ray radiation that have atomic wavelengths so the wavelength is really on the order of the size of an atom so what kind of wavelength do we need to study ultra short dynamics ultra-fast dynamics we can first think about what kind of wavelength we need when we want to construct an ultra short pulse I've drawn here two pulses to the left a slightly longer pulse to the right a shorter pulse and now if you think about squeezing the left pulse together such that it becomes shorter and shorter you see visually that the wavelength also needs to shrink so we need shorter wavelengths for the shorter the pulse we want to make so this will be located somewhere here in this region of the electromagnetic spectrum and another important thing that we need to keep in mind is if we want to take pictures by x-ray diffraction we are limited so we can only resolve structures that are of about the same size as the wavelength we used to take our diffraction image so if we want to take a picture of something with atomic resolution our wavelength needs to be of atomic size as well and this places us in the region of x-rays drawn here but have a wavelength of less than a nanometer so we can establish that we want small wavelengths in general we have two additional requirements that I would just touch upon very briefly first we need very brilliant pulses because the pulses are so short we need to have a lot of light in the short pulse you can think about taking a picture in a dark room with a bad camera you won't see anything so we need very bright flashes of light another requirement is we need coherent laser light so we cannot just use any light but it needs to have certain properties like laser light unfortunately the lasers that you can buy commercially do not operate in the region of the electromagnetic spectrum that we are interested in so we need to come up with something new and I will show you how we can generate ultra short pulses both in the laboratory where we can generate pulses that are very short and extend up to maybe the soft x-ray region and another method to generate ultra short pulses is at free electron laser sources where we can go really to the hard x-ray regime but first I'd like to go to the laboratory so in the laboratory it's possible to generate an ultra short pulse by using a process that's called high harmonic generation and high harmonic generation we start off with a high intensity pulse that's the red pulse coming in from the left which which is focused in a gas cell and from there it generates new frequencies of light so the light that comes out is no longer red but it's yeah violet blue we cannot see it with the naked eye so that's an artist's impression of how high harmonic generation works before going into more detail about why this method is so good at producing ultra short pulses I'd like to mention that this is only possible because we have the high intensity driving pulses the red laser pulses available this goes back to work by Donald Strickland and Gerard who were awarded the Nobel Prize in the year 2018 in physics for this work that has been done in the 80s now we're coming to the only equation of this talk which is this equation that relates the energy width and the time duration of the ultra short pulse by the law of Fourier limits we cannot have pulses that are very short in time and at the same time very narrow in energy but we need to choose one so if we want to have pulses that are very short in time like the pulse that I've shown here on the bottom that is actually only 250 at a second long so even shorter than a femtosecond then we need to have a very broad which built an energy and this means combining a lot of different colors inside of this pulse and this is what makes high harmonic generation so efficient at creating ultra short pulses because the spectrum that the colors that come out of high harmonic generation are shown here and they really span along with so we get a lot of different colors with about the same intensity and you can think of it like putting them all back together into one at a second pulse that is very short in time this method has really made a big breakthrough in the generation of ultra short laser pulses we see here a plot of a time duration of laser pulses versus the year and we see that since the invention of the laser here in the mid 60s there was a first technological process progress and shorter and shorter pulses could be generated but then in the 80s there was a limit that had been reached of about five femtoseconds I believe and we could not really go far farther than that and only with high harmonic generation that sets in here shortly before the year 2000 we were able to generate pulses that are of a femtosecond duration so that really touch the time scale of molecular motion the current world record is a pulse that is only 43 milliseconds long established in the year 2017 so that's really the time scale of electrons and we can do all sorts of nice experiments with it where we directly observe electronic motion and atoms and molecules this is all very nice but it has one limitation we cannot go to hard x-rays at least not right now so high harmonic generation cannot produce the kind of very short wavelengths that we need in order to do x-ray diffraction experiments with atomic resolution so if we want to have ultra short pulses that have x-ray wavelengths we need to build right now very complex very big machines the so-called free electron lasers now this would be a specific light source that can produce ultra short pulses with x-ray wavelengths in itself the x-ray wavelengths is not so new we know how to take x-ray images for about a hundred and thirty years and already in the 50s Rosalind Franklin who is looking at a microscope here was able to take a picture of DNA an x-ray diffraction pattern of the DNA double helix that was successful in revealing the double helix structure of our genetic code but this is not a time-resolved measurement so think of it as you have a molecule that is in crystalline form so it's not moving around and we can just take an x-ray image of it it's not going anywhere but if we want if we want to take a picture of something that is moving we need to have very short pulses but we still need the same number of what we call photons light particles or think of it as we need more brilliant x-ray flashes of light then we could obtain before and there was very nice technological development in the past 50 years or so where we were able to go from the x-ray tube to newer light sources called synchrotrons and today free electron lasers that always increase the peak brilliance in an exponential way so we can take really brilliant really bright x-ray flashes right now I cannot go into the details of all of that but I found a very nice talk from two years ago that actually explains everything from synchrotrons to FEL still available online if you're interested in this work and as always if something is scaling exponentially most of you will be familiar with Moore's law that tells us about the yeah exponential scaling of transistors if something grows this fast it really opens up a new series of experiments of new technological applications that no one has thought of before and the same is true with free electron lasers so I'm going to focus just on the most brilliant light sources for x-rays right now the free electron lasers that are at the top right here of this graph have been around for maybe 10 years or so I cannot go into a lot of detail on how to generate utter short pulses with x-rays so I'd like to give you just the very broad picture of how this works first we need a bunch of electrons that is accelerated to relativistic speed this sounds very easy but is actually part of a two kilometer long accelerator that we have to build and maintain now we have this bunch here of electrons shown in red and it's really fast and now we can bring it into something that is called an undulator that is a series of alternating magnets shown here in green and blue for the alternating magnet and you may remember that when we put an electron that is a charged particle into a magnetic field the Lorentz force will drive it away and if you have alternating magnets then the electron will go on a sort of wiggly path in this undulator and the electron is a charged particle as it is wiggling around whenever it turns around it will emit radiation that happens to be in the x-ray region of the electromagnetic spectrum which is exactly what we want we can watch this little movie here to see a better picture so this is the undulator seen from the side we now go inside of the undulator we have a series of alternating magnets now the electron bunch shows up and you see with wiggly motion as it passes with different magnets and you see the bright x-ray flash that is formed and gets stronger and stronger as the electron bunch passes the undulator so we need several of these magnet pairs to in the end get the very bright x-ray flash and at the end of the undulator we dump the electron we don't really need this electron bunch anymore and continue with a very bright x-ray flash this whole process is a bit stochastic in nature but it's amplifying itself in the course of the undulator this is why the longer the undulator is the more bright x-ray flashes we can generate this whole thing is kind of complicated to build it's a very complex machine so right now there are only very few free electron lasers in the world there's one in California called LCS one currently being upgraded to LCS two there are several in Europe there's one in Switzerland in Italy in Hamburg so there's a flash that does not operate in the hard x-ray regime that was the kind of first free electron laser there's the most recent addition to the free electron laser zoo it's the European XFL also located in Hamburg and then we have some of these light sources in Asia in Korea sub Korea Japan and one currently under construction in Shanghai I'd like to show you a bit more details about the European x-ray free electron laser because it's closest to us and at least closest to where I work so the European XFL is a 3.4 kilometer long machine that is funded by in total 12 countries so with Germany and Russia paying the the most and then the other 10 countries also providing to the construction and maintenance costs this machine starts at the Daisy campus that is shown here to the right of the picture and then we have first an accelerator line for the electrons that is already 1.7 kilometers long and where we have electrons reach their relativistic speed then the undulator comes in so the range of magnets where the x-ray flashes are produced the x-ray flashes then cross the border to Schleswig-Holstein shown here on the other side in a new federal state they they reach the experimental hall we have in total six experimental end stations at the European XFL that provide different instrumentation depending on which kind of system you want to study you need slightly different instruments and it's not only for for taking molecular movies but the XFLs used among others for material science for the imaging of biomolecules for a femtosecond chemistry all sorts of things so really wide range of applications it's right now the the fastest such light source it can take 27,000 flashes per second which is great because every flash is one picture so if you want to take a lot of snapshots if you want to generate a lot of data in a short time it's great to have as many flashes per second as possible and as you can imagine it's kind of expensive since there are so few free electron lasers in the world to to take measurements there the complete price tag for constructing this machine it took eight years and cost 1.2 billion euros which may seem a lot but it's the same amount that we spend on concert halls in Hamburg so kind of comparable now when you yeah when you factor in maintenance and so on I think a minute of x-ray beam at such an XFL costs several thousands of tens of thousands of euros in the end so getting measurement time various complicated and their committees that select the most fruitful approaches and so on so in order to not to to waste our dear taxpayers money with this I'm I'd like to make a small comparison of the light sources that I've introduced now so I introduced the laboratory light sources and the XFL light source in general in the laboratory we can generate very short pulses of less than 100 milliseconds by now in the XFL we are limited to something about 10 femtoseconds right now in terms of brilliance the XFLs can go to much more bright pulses simply because they are bigger machines and high harmonic generation in itself is a kind of inefficient process in terms of wavelength x-ray free electron lasers enable us to reach these very short wavelengths the x-rays that we need to get atomic resolution of diffractive images in the laboratory we are a bit more limited to maybe the soft x-ray region there's another important thing to keep in mind when we do experiments that's the control of pulse parameters so is every pulse that comes out of my machine the same as the one that came out of my machine before and since the XFL produces pulses by what is in the end a stochastic process that's not really the case so the control of pulse parameters is not really given this is much better in the laboratory and in terms of constant availability it would of course be nice if we could do more experiments in the lab than at the XFL simply because the XFL so yeah expensive to build and maintain and we have so few of them in the world and you can see this this tunnel here it stretches for yeah two kilometers or so all packed with very expensive equipment so I'd like to show you a brief example of what we can learn in ultrafast science so this is theoretical work that we did in our group so no experimental data but still nice to see this is concerned with an organic solar cell so we all know solar cells they convert light sunlight to electric energy that we can use in our devices the nice thing about organic solar cells is that they are portable very lightweight and we can produce them cheaply the way that such a solar cell works is we have light shining in and at the bottom of the solar cell there sits an electrode that collects all the charges and creates an electric current now light creates a charge that somehow needs to travel down there to this electrode and in fact many of these charges so the important thing when we build such an organic solar cell is that we need a way to efficiently transport these charges and we can do so by putting polymers inside so polymer is just a molecule that is made up of two different or two or more different smaller molecules and one such polymer that should be very efficient at transporting these charges is BT1t that is shown here the name is not so important it's an abbreviation because in BT1t when we create a charge at one end of a molecule here at the top it travels very quickly to the other side of a molecule and you can imagine stacking several of these BT1t's or yeah especially of the t's together putting it in this material and then we have a very efficient flow of energy in our organic solar cell so what we did was we calculated the ultrafast charge migration in BT1t shown here to the right the pink thing is the charge density that was created by an initial ionization of the molecule and now I'll show you the movie how this charge is moving around in the molecule so you can see the individual atoms moving the whole molecule is vibrating a bit and the charge if you look closely is locating on the right half of a molecule within about 250 femtoseconds now we cannot observe this charge migration directly by looking at this pink charge density that I've drawn here because it's at least for us not experimentally observable directly so we need an indirect measurement an x-ray absorption spectroscopy that I showed you in the beginning could be such a measurement because in the x-ray absorption spectrum of BT1t but I've shown here in the bottom left we see distinct peaks depending on where we charge is located initially the charge is located at the top sulfur atom here in this molecule and we will see a peak at this color once the charge moves away to the bottom of a molecule to the other half we will see a peak at the place where nothing is right now because the charge is not there but if I start this movie we will again see very fast charge transfer so within about 200 femtoseconds the charge goes from one end to the molecule to the other end of the molecule and it would be really nice to see this in action in a future XFL experiment but the process is very long you need to apply for time at an XFL you need to evaluate all the data so maybe a couple of years from now we will have the data available right now we are stuck with this movie that we calculated now towards the end of my talk I'd like to go beyond the molecular movie so I've shown you now how to generate the light pulses and an example of what we can study with these light pulses but this is not all we can do so when you think of a chemical reaction you might remember high school chemistry as something like this which is always foaming and exploding and nobody really knows what is going on so a chemical reaction quite naturally involves molecular dynamics for example the decomposition of a molecule to go from here from the left side to the right side the molecules will somehow need to rearrange so all the atoms will have moved quite a bit we've seen already how we can trigger these chemical reactions of these molecular motion that was part of a molecular movie but it would be really cool if we could control the reaction with light so the way to do this it's not currently something that is possible but maybe in the near future would be to implement a sort of optimization feedback loop so we would record the fragments of our reaction send it to an optimization routine that will also be quite complicated and we'll need to take into account the whole theory of how light and matter interact and so on and this optimization routine would then generate a new sequence of ultra short pulses and with this feedback loop it might be possible to find the right pulses to to control chemical reactions taking into account the quantum nature of this motion and so on right now this is not possible first because the whole process of how we can generate these ultra short pulses is not so well controlled that we could actually implement it in such a loop and also the step optimization routine is more complex than it looks like here in this picture so this is something that people are working on on at the moment but this was be something like the ultra fast wish list for next Christmas not this Christmas so we've succeeded in taking the molecular movie but we would also like to be able to direct the molecular movie so to go beyond just watching nature but controlling nature because this is what humans like to do best fortunately or unfortunately it depends so I'd like to just show you that this is really an ultra fast developing field there's lots of new research papers every day every week coming in studying all sorts of systems when you just take a quick and dirty metric of how important ultra fast science is this is the number of articles per year that mention ultra fast in Google scholar it's exponentially growing at the same time the number of total publications in Google scholar is more or less constant so the blue line here outgrows the green line considerably since about 10 years so what remains to be done we've seen that we have light sources available to generate ultra short pulses but as always when you have better machines bigger machines you can take more fancy experiments so it would be really nice to develop both lab based sources and free electron laser sources so that we can take more interesting more complex experiments another important challenge that is what people in my research group where I work are working on is to improve theoretical calculations because I did not go into a lot of detail on how to calculate these things but it's essentially quantum mechanics and quantum mechanics skates very unfavorably so going from a very small molecule like this glycine molecule here to something like a protein is not doable simply it you cannot compute this with quantum mechanics so we need all sorts of new methodology to yeah to better describe larger systems we would in general like to study not only small molecules and not only take movies of small molecules but really study large systems like this is the FMO complex that is a central and photosynthesis or solid states that are here shown in this crystalline structure simply because this is more interesting for biological for chemical applications and finally as I've shown you it would be cool to directly control chemical reactions with light so to find a way how to replace this mess with a clean light pass with this I'm at the end I'd like to quickly summarize femtosecond dynamics are really fundamental in biology chemistry and physics so more or less the origin of life is on this time scale we can take molecular movies with ultra short laser pulses and we can generate these pulses in the laboratory or at free electron lasers with different characteristics and we would like to not only understand these ultra ultra past phenomena but we would also like to be able to control them in the future with this I'd like to thank you for your attention and thank the supporting institutions here that funded my PhD work well that was an interesting talk I enjoyed it very much I guess this will spark some questions if you want to ask Carolina question please line up behind the microphones we have three in the aisles in between the seats if you want to leave please do so in the door here in the front and until we get questions from the audience do we have questions from the internet yes big fat random user is curious about the design of the x-ray detector do you have any information on that that's also very complex I'm I'm not a big expert in detectors at this point I'd really recommend watching the the talk from two years ago that explained a lot more about the x-ray detectors so what I know about the x-ray detector is that it's very complicated to process all the data because when you have 27 thousand flashes of light it produces I think terabytes of data within seconds and you need to somehow be able to store them and analyze them so there's also a lot of technology involved in the design of these detectors thank you so the first question from microphone two in the middle so my question is please go close to the microphone my question is regarding the synchronization of the detector units when you pointing to free electron lasers how you can achieve the synchronization this is also very complicated it's easier to do in the lab so you're talking about the synchronization of essentially the first parts and the second parts right so in the lab you typically generate the second parts from part of the first parts so you have a very natural alignment at least in time of these two pulses the x-ray free electron lasers have special timing tools that allow you to to find out how much is the time delay between your two pulses but it's true that this is complicated to achieve and this limits the experimental time resolution to something that is even larger than the time duration of the pulses so now next question from microphone number three yes I remember in the beginning you explained that your measuring method your pulse usually destroys your molecules that's a bit of a contradiction to your idea to control you know in principle yes but so in the case of control we would like to use a second pulse that does not destroy the molecule but for example or at least destroys it in a controlled way for example so there's a difference between just blowing up your molecule and breaking apart a certain part that we are interested in and that's what we would like to do in the in the control case so we would like to be able to to control for example the the fragmentation of a molecule such that we only get the important part out and everything else just goes away thank you so then another question from microphone two in the middle so thank you for the talk I was interested in how large structures or molecules can you imagine with this laboratory conditions and with this x-fell thing sorry can you repeat it so how large molecules can you do imagine in this laboratory with this higher mark so how large is not really the fundamental problem and people have taken snapshots of viruses or bigger biomolecules if you want to the problem is rather how small can we get so yeah to take pictures of a very small molecule currently we cannot take a picture of an individual small molecule but what people do is they they create crystals of the small molecule stacking several of them together and then taking images of this whole crystal for single particles I think right now about the scale of a virus nanometers thank you okay do we have another question from the internet we have so this is concerning your permanent destruction of forces I guess how do you isolate single atoms or molecules for analyzing between the different exposures yes excellent question so molecules can be made available in the gas phase by so if you have them in a in a solid somewhere and you heat that up they will evaporate evaporate from the from that surface this is how you can get them in the gas phase this of course assumes that you have a molecule that is actually stable in the gas phase which is not true for all molecules and then the the hard thing is to align all three things so the pump parts the pro parts and the molecule they all need to be there at the same time there are people doing whole PhD thesis on how to design gas nozzles that can provide this stream of molecules so you're basically really having a stream coming from a nozzle yes a very thin stream I guess yes then you're exposing it like a regular interval and of course you try to hit as many molecules as possible so this is especially important when you do pictures of crystallized molecules because crystallizing these molecules is a lot of work you don't want to waste like 99% that just fall away and you never take snapshots of them thanks so another question from microphone 3 how do you construct this movie I mean for every pulse you have a new milk molecule and for every molecule is oriented differently in space and has different oscillation modes how do you correlate them I mean no movie I mean every molecule is different at the previous one yes that's so first what people can do is align molecules so especially molecules that are more or less linear you can force them to to be oriented in a certain way and then there's also a bit of a secret in the trigger pulse that first sets off this motion for example if this trigger pulse is a very strong photo ionization then this will kill off any sorts of vibrational states that you have had before in the molecule so in this sense the trigger parts really defines a time zero that should be reproducible for any molecule that shows up in this stream and the rest is statistics thank you so there's another question on microphone 3 are there any pre pulses or ghosts you need to get rid of sorry again you have to control our pre pulses or ghosts doing this effect for measuring that I'm not really sure of since I'm not really conducting experiments but probably and another one from the middle from microphone 2 please I suppose if you apply for experimentation time at the X fel laser you have to submit very detailed plans and timelines and everything what and you will get a time window for your experiment I guess what's going to happen if you're not completely finished within that time window are they easy possibilities to extend the time or they do they just say well you had your three weeks you are out apply in 2026 yeah I think it's the regular case that you're not finished with your experiments by the time your beam time that's that's how it usually goes it's also unfortunately not three weeks but it's rather like 60 hours delivered in five shifts of 12 hours so yeah you write a very detailed proposal of what you would like to do submitted to a panel of experts both scientists and technicians so they they decide is it interesting enough from a scientific point of view and is it feasible from a technical point of view and then once you are there you more or less set up your experiment and do as much as you can and if you want to come back you need to submit an additional proposal so yeah I think most experimental groups try to have several of these proposals running at the same time so that there's not a two-year delay between your data acquisition but yes no no possibility to extend it's it's booked already for the complete next year the schedule is fixed thank you so I don't see any more people queuing up if you want to pose a question please do so now in the meantime I would ask the signal angel if there's another question from the internet another question about the dimensions of all those machines the undulator seems to be rather long and contain a lot of magnets do you have an idea how long it is and how many of those electromagnets are in there yes sorry I didn't mention it's about I think 170 meters long in the case of a European XFL I'm not sure about the dimension of the individual magnets but it's probably also in the hundreds of magnets magnet pairs so is there more excuse me there's a question on the microphone number number three it's regarding the harmonic light is closer to the microphone at the harmonic light generator that you were showing at the very beginning just before the one that won the Nobel Prize can you also produce light in the visible range or it has to be in the invisible range the high harmonic generation so in the well in the in the visible range you cannot create pulses that are so short that they would be interesting for what I'm doing the the pulse that comes in is already quite short so it's already femto seconds long they just converted into something that is fractions of a femto second long and yeah in the in the visible range that's kind of the limit how short your pulse can be so it's not a good candidate for hyperspectral image in light source no we do need another kind of technique I guess well I mean you're you're just a kind of yeah limited what what short pulses you can you can generate with which wavelength thank you so again a question to the single agent are they more questions for from another one about the lifetime of the molecules and the beam how fast are they degrading or how fast are they destructed so probably the question is about how fast they are destructed before so either before our pulses hit hit the molecule the molecules should be stable enough to survive in the gas phase from the point where they evaporate it until the point where the pump and the propods come together because otherwise it does not make sense to study this molecule in the gas phase when the the propods hits and it flows apart I guess picoseconds until the whole molecules like instantaneous yeah so I don't see any more questions on the microphones and we have a few minutes left so if there are more questions from the internet we can take maybe a more one or two more give me a second for people leaving already please look if you have taken trash and bottles with you so there's one very very technical question how do you compensate the electronic signal that the electronic signal reaction is probably slower than x-ray or light or spectrum changes at one moment or at one particular moment that was interesting to analyze I don't understand the question though I think I understand the question but I don't have the answer because again I'm see that's a problem of speaking to a technical audience you get all of these very technical questions yeah the data analysis is not instantaneous so the data is yeah transported somewhere safe in my imagination and then yeah taken from there so this data analysis does not have to take place on the same time scale as the data acquisition which I guess is also because of the problem that was mentioned in the question yeah I think you might interrupt here maybe it's also about the signal transmission like the single rising of the single electrical signal transmissions because this would probably require bandwidths of several megahertz gigahertz I don't know to transport these very fast results yeah I think that's also a problem of constructing the right detector that has been solved apparently because they can take these images and on the other hand we have 10 gigabit ethernet so we get faster and faster electronics more questions from the internet does not look like it also the time is running out so let's thank Carolina for her marvelous talk


What's up YouTube? This is John Hammond and we're looking again at the Natus war game from over the wire so now we're on level 18 and Let's go ahead and run our script to see what it is that we are actually working with here Looks like the page returns. Please log in with your admin account to retrieve credentials for Natus 19 Okay, so this doesn't look like the sequel injection or the Command execution that we had seen some of the other levels. Maybe this is something new We have a username and password input fields here But let's take a look at the source code and try to analyze what we can Paste that in the for our get request and now we can de-entitize what that returns for us and remove all the break tags with some Find and replace magic. So the PHP code starts out telling us we have a max ID variable set to 640 the comment here 640 should be enough for everyone don't entirely know what that means just yet So we'll keep reading Here's one function is valid admin login Determines if the request username is equal to admin this method of authentication appears to be unsafe and has been disabled for now Okay, so it just that function returns zero it pretty much does nothing just just return zero, okay But that kind of nerfs our ability to log in as admin because if we were to Pass along this request with the username field just trying to log in as admin it wouldn't work for us. So, okay Whatever that's not gonna do anything. It just returns zero. So this function is valid ID Just determines whether or not it's a number the argument that's passed to it. The idea is a number create ID User Doesn't look like user is actually used in this function But it does take advantage of this max ID variable It's global scope right on the outside and it creates a random number from one to six hundred and forty That's what that ran function does. Okay, so create ID is kind of random Debug messages we can use with a get parameter That's pretty handy to know in case it gives us any valuable information, but my session start looks like it will Determine whether or not a session ID already exists in the cookie a php session ID and if it's a valid or not If that is the case It will go through with this code. If not, it does nothing. There is no else statement with this. It looks like so If the session has not already started looks like it will just say it fails or turn false Otherwise, it will create a new session Determine if you're an admin and debug Okay, it looks like it closes that admin variable There sets that session admin equal to zero Okay, so that locks us out again of being admin that still won't work, right there's is valid admin log and return zero session admin being set to zero so it Session was old admin flag set resets us. So it looks like it never really lets us be that session admin Yeah, even this session admin equals zero, but later on in this Print credentials function. It looks like it's trying to determine if session admin is equal to one Then it will say you're an admin credentials from next level are here So we have to set session admin to one But we can't in this code At least what we've read so far Well, otherwise we're logging as a regular user a regular user. Sorry log in to admin to retrieve credentials Huh If the session has started it will display that Otherwise it will Read the read the request for us Session admin is going to be zero because that is valid admin login is zero And it will show the form if we haven't if we haven't logged in. Okay, so let's just Try it out Let's go ahead and make a get a post request here. We'll pass in the data Make sure we actually post to the real page not the source code I'm going to change the URL up there Username can equal Please And password Can be subscribe Shameless self advertisement Run this So we get here your login as a regular user login as an admin to retrieve credentials for natus 19. What the heck? Okay I don't know Why we Aren't an admin other than the fact that I tried to log in as Please subscribe so clearly we're not going to be an admin just like that Let's print out what cookies we have here because it looked like in the source code It was showing us The php session variable php session id being set to 260 So that must be what that source code gave us as the random number random between 1 and 640, but There's no way we could otherwise be an admin Because it wouldn't it wouldn't let us use any of those like session admin variables. So maybe Is is one of these session id is just just the admin id? I'm going to do a little bit of research here. Let's fire up fire fox And I just wanted to show this to you because php session id Is something we should probably get to know Uh, I know there is a php session id php.com like article on this thing There's gotta be session id php sess id will actually tell us what this thing is Okay, it looks like it just gets in sets session functions It won't tell us anything about what that php session id is Other than there is one and it looks like it has to be stored Stack overflow php uses two methods of keeping track of sessions cookies are enabled like in your case it uses them Okay, so that must be what we're working with so looks like we have to change that cookie variable php session id To one of the numbers between 1 and 640 because maybe one of them will be an admin id So let's try that. Let's get the page with a session id set to something else. So let's get with cookies equals php session id set to 1 right, it's got to be a string here I don't need the cookies anymore Because I'm pretty trusting it will return says your login is regular loser a regular loser Um, and let's actually move move forward from this here because we want to see okay that one clearly wasn't the admin user So what else can we get that might be? We want to determine in a loop Because we're getting the page over and over and over again with a new session id if we are the admin so if you are an admin Was the string that was in it, right? Let's see content response Dot text can just be the content variable that we're working with in content Actually, probably want that down here print got it and then print the content just print trying id or session id and we will loop through for session id in range of one to six hundred and forty We can go up to 641 since that will be inclusive here and let's Run string of our session id Um Before we run do this I should have actually checked that or save that source code because I wanted to know what that would be That string because I honestly honestly forget. So let's just check Let's just do one more get request to make sure that is the correct string Determining if we are not an admin. Let's print response dot text De-entitize I really should just save this code. I'm sorry.  Okay. That works just fine for us. Good. Uh, let's put this in a new pane in case we need it again and Let's start the attack session id get with the cookies php session id being set as The string here getting the content determining if you are an admin is in the content If it is it will get it and then otherwise it will print trying session id And let's see how this looks. I'm gonna do this in the command line So we can python that is 18 dot pi trying 1 2 3 etc etc etc So I'll let this run and Actually, I should probably put a break when we get it And then print the session id that we got Now let's run this And I'll pause the video so I'll pause the recording. So once it's done We can see what the password is. So I ran through it and it didn't work So let's take a look at the code and see what's wrong Oh, we were sending that to the source code all along I'm a fool So that code probably would have worked I'm gonna let this uh Pause the video here pause the recording so I can see Okay, so the script returned now and I did get the correct session id at id number or admin id at id 138 So here we've got the password You are an admin the credentials for next level are natus 19 password This guy And that's it So the session id We're passing in to our request but Since that's not part of the session object, it doesn't look like it's staying in the session object itself It looks like it's just going for that request So that's peculiar note And I really want to apologize about sending it to the wrong Page up there with the index or still in the url. I'm sure you were probably screaming at me the entire time I need to remember to change that But thank you guys for watching. Hope you enjoyed this. Let's go ahead and put this new Um new password in a new script. Let's put this in natus 19 And Let's go ahead and see what this level is asking us to do Cool All right. Well, hey, thank you guys for watching. Hope you're enjoying these videos If you did like the video, please do hit that like button Leave me a comment. Let me know what you think what you like what I can do better What else you'd like to see Please subscribe and if you really really want to support me Please head on over to my patreon account. So thanks again guys. I'll see you in a later video


kind of like the miscellaneous stuff that you'll pick up in the problem so anything that we haven't picked up yet that is is not in the selling is probably part of the general and administrative expenses and so we're going to have here in this case we take a look at this we have salaries of administrative salaries of 11 000 so that's going to be in the you know the office the account department being included in there so we'll just have salaries for the administrative salaries 11 000 it's a fixed cost so we're just going to put 11 000 all the way across for July, August and September and we could total that up for the quarter summing the July, August and September and enter all right and then we also have this loan on the books as well so we're going to group that into the selling and I mean into the general administrative type expenses so the loan is on the books at we can see the 500 000 long term note so we're going to put the long term note in this section as well for our budgeting and we can see that we have an interest on it we're not going to put the loan we're going to put the interest on the loan and then so we have the long term monthly interest that we're going to pay and we've this problem has simplified it down so we're going to take the monthly interest rate if you see a problem that gives you the you know the yearly interest rate then of course you would have to break it down to a monthly rate so we've already broken down the rate meaning we took the yearly rate basically divided by 12 and just given the monthly rate which is 1% here so we're going to take the interest on long term note which equals that 500 000 times 0.01 so remember that obviously we moved the decimal over two places 0.01 equals and we can do that all the way across we could copy it 500 000 times 0.01 it's going to be 5000 again equals the 500 000 times 0.01 and then we could of course sum that up equals the sum of 5000 5000 5000 July August September gives us the 15 so we're just going to add those two up and that'll give us our total expenses here so we'd say this equals the 11 plus the five tab August equals the 11 plus the five tab and September equals the 11 plus the five tab we could sum this up two ways we could say the total equals the total for the quarter plus the total for the quarter or we can check that number by highlighting these three July August September gives us the 48 000 that is our total expenses okay so now let's move on to calculating part of the cash budget now when we start thinking about cash we're going to have to break down the idea of when we make a sale are we going to collect all the cash when we sell it or are we going to collect the cash afterwards at some point in the future and and when we think about our cash flow budget that's going to be important obviously so that's what we're going to basically break down and we're going to use in our cash flow budgeting as we go so let's take a look at what basically our problem says here it's saying that of our sales we're going to sell 30 percent for cash so we're going to collect the cash at the point of sale in the same month and then we're going to say that 70 percent is going to be sold on credit and we're going to say that the stuff that was sold on credit we are going to collect that cash in the following month so taking those into consideration let's think about what the cash flow would be projected to look like we're going to start with the total budgeted sales again so we're going to say what was our sales for July both cash and on account and we're going to get that from our sales budget so in July I'm going to hit equals I'm going to scroll all the way up to the top again scroll all the way at the top and here's our sales budget for July we're going to sell $494 and that's what we're going to that's what we're going to collect and well that's how much we're selling in dollars units but of course we're not going to collect it all in dollars yet and then in August we're going to say this equals and we're going to scroll all the way up to our sales budget again and we're looking for August August in dollars for 7400 tab and September we're going to say September scrolling all the way up to our sales budget we're going to sell 4824 so again we're measuring that in dollars but we are I have not yet collected all the money yet some of it was sold on account some of it was sold for cash more specifically we're going to have cash sales of 30 percent and sales on credit 70 percent so let's just first break that out and see what that looks like so we're going to say that of course in July we had total sales 494 four times 0.3 or 30 percent enter and then I'm going to say on credit