 Right, so good morning everyone. I'm I'm chairing the session this morning and We're gonna start With Aristides Markano from Delaware State University. He's going to give the second half of his Lecture Thank you professor, okay morning everybody I Have today this second part. It's mostly about Applications yesterday we were talking about from the principles of the photo thermal ideas. So we actually Discussed that but the photo thermal method is measuring so we actually show that you can measure the heat that is generated after absorption of photons in matter and And that's they also we show that this is a universal effect that always happens You cannot get rid of that because this is just a fundamental principle of thermodynamics We know that that's the second principle of thermodynamics that sooner or later. You will have heat there being generated and Also, we discussed the idea of the photo thermal lens and the photo thermal mirror Like two techniques that at the beginning and people consider then they were just another way of measuring absorption but in in this lecture we will see that this Method actually measure something different from absorption and you can actually combine this photo thermal spectroscopy with regular Absorption spectroscopy to provide interesting information about properties of matter and that's important because today we are Generating new kind of materials Graphene is one of the examples of these kind of new materials. You have people are in things studying 2g crystals and semiconductor 2d crystals and Possibilities for technical applications in photonics are immense huge I Just will start my lecture with this picture actually this picture. I notice in the program that you have My photo thermal microscope This is an excellent application of these ideas and that was a paper published in science about 12 years ago But these people are several groups in the world. They are published in that what is interesting They were doing some photo thermal Scanning that the photo thermal effects and they were scanning and these they claim that each of these peaks represent one nanoparticle One nanoparticle of 5 nanometers diameter Which is very very small resolution as I said, that's an interesting idea Is that the resolution of the microscope is not given by the diffraction theory by the diffraction limit? It's well below the diffraction limit 5 nanometers is given by the size of the absorbing object So the size of the absorbing absorbing object that you have the size of an atom you can in principle Detect one atom with this map That's very very interesting, but I think this is quite interesting paper There are other papers showing these applications, but the difficulty is still there's a lot of technical difficulties because a lot of effort I guess a photograph like that This is my look for the lecture today and First while we are doing that we are just using the method to characterize properties of matter and We are going to talk a little bit about the acrobatic character of the method that actually is reinforced By the most mismatch idea So we also discussed this idea in the previous lecture that you can actually have an excellent and optimized signal if you call me you prove and focus your pump and Still this idea is around so more people are being convinced that this is the best way of doing the experiment but at the same time this kind of arrangement Provides some necromaticity is something this is very important because when you have doing a spectroscopy You know that the refraction index has some dispersion So you can have dispersion of the some these Aberrations or chromatic operations in your optics you you probably have what they call very expensive optics to correct For that and it does the reason all these Cameras and all everything is very very they are very expensive because of all this Take technology that you need to use to eliminate the chromatic operations But I'm going to show you that this method provides automatic correction for that That's not an unexpected and also I'm going to talk about the possibilities for doing real spectroscopy and in this case infrared near infrared spectroscopy with it with the regular Titanium sapphire laser, which is for less the it's a fun to second laser But we use the laser in the CW regime. We didn't use modlock So we just use has a CW laser and we do we just use has an infrared source a near infrared source of light And then we just will show first and device that we built using a Very complex laser system that includes an optical parametric oscillator Which is the problem of that so you can do the experiments You can get a lot of information and you can prove they'll make the proof of the idea of the importance of the idea But still, you know, it's not practical because these systems are very they cost a lot of money I learned today that the OPO is not working anymore. So they're difficult to work with they have me and need to have very costly maintenance and problems like that and Later, I'm going to say that you can do this spectroscopy. Thanks. Thanks to the Sensitivity we can have you can do this spectroscopy with the normal lamp with an arc lamp Which is a regularly uses the technology that exists over 100 years and this technology Is very well known. It's very well developed. It's still there. They cost some money, but not has a laser Not has a laser. So it's still the exact and they're tunable. You can actually tune and get some Spectra from them. That's the same way you do in the normal commercial spectrophotometer And then we are going to show why for the thermal spectroscopy is not the same that absorption spectroscopy With applications for fluorescent samples and for scattering samples. So usually the samples they have For example, you take blood Blood has a people need to purify blood you remove all the blood cells and everything and then get the plasma And then you still have scattering You still have turbidity there and usually we are going to analyze water You know that there are a lot of different particles there and they produce some turbidity some scattered And they can affect your measurement your absorption measurements, of course Okay, and fine. This is just in a scheme Simplify scheme what is happening when the light go past interact with matter so you can have here your your Insidious light right here. It could be a laser. It could be any kind of light And you have this is this we have block represent the sample and then you may have the first experiment The first effect you can have you have you will have some reflection So the reflection is going back in the same direction, but it's going back and people do some reflectance Experiments so you can measure in the spectra in reflection. That's very useful when these samples are not transparent or Pay so people do that for metallo optics mostly and they can analyze people also do that that that affects the polarization of light So you do what is the so-called ellipsometry that the uses regularly used for analysis of films and Semiconductors and everything and they are very very commercial devices has been very well developed during the last 60 or 70 years Then you have scattering on the scattering is a natural phenomena that actually happens And this is corporate it can be of different types It could be the typical Elastic scattering where there is no change of energy in the incident for them There is only change the direction and polarization And and it's going into any direction Including the original direction. So you have some scattered light It means that you can you to detect that you usually put the detector Most of the people they use put a detector in the perpendicular direction So they put the lens to collect that light into the detector But to collect all the light It's not that easy. You cannot do that people using a sphere So they will be where they go scattering the spheres and it's a nice device That has a lot of detectors and everything or sometimes one detector very nice Optics there to develop and also they call some money in any way and You can have the transmitted light something is being transmitted. That's what you use in normal commercial Spectroscopy and absorption spectroscopy. You just measure the transmission of light But you also can have some things you can have generation of sound You can have generation of sound so you can have some photo acoustic effects You can have some photo thermal effects You can have some photo mechanical effects For example, there is an effect that you have for example, you have sometimes you have a liquid and decide the liquid There are some particles their nanoparticles and there are some the so-called sorrid effect You generate a gradient a gradient of temperature So you generate also a gradient of concentration at the same time This is actually very well known for people who work in the oil industry because they need to separate the components of oil and they use this Gradients of temperature to do that sometimes and You can have Photochemical effects for the chemical effects. It means that you there is a very well known phenomenon You can generate singlet oxygen singlet oxygen is an excited level of oxygen That is more or less metastable But it's terrible is what you say is oxidizing our so it actually regulates life and death of cells And it's very important because if you can locally generate singlet oxygen and you kill cancer So people are doing that. This is so called photodynamic therapy. That's a photo chemical effect It means that there is some chemistry so an energy being used for chemical reactions From the back and you can have some luminescence. So luminescence is very broad You can have fluorescence. You can have Raman. You can have phosphorescence Any other effect maybe you still within discovered, but we don't we don't know but this is only linear regime Linear so we're talking about linear regime. You increase the intensity of your laser right here So now my laser is dying. It has no intensity But anyway my pointer is dying But when you have increased here the intensity, you will have no linear effects So you have no linear reflection or linear scattering. You can have coherent stocks and anti stocks spectroscopy you can do Care effect you can do pocule effect you can it's infinite It's infinite as the kind of effects you can generate with that if you increase it Because you increase a little bit you get more and more effects of course matter You know a matter and what it does it usually shows one the most important effect is the most Some samples they have they are good for this all the samples are good for something different I you see this variety of things can we actually What we know as physicists is the energy you cannot destroy the energy so you have conservation of energy and Whatever energy you have at the beginning right here should be equal to the incident energy that you have Should be equal to the transmitted energy what is left plus the fluorescence energy plus the thermal The energy used for thermal effects plus the energy used for scattering plus the energy used for reflection and so on So you can imagine that this in equations could be very complex But happily happily in some samples you maybe you have the sample that has Dominant fluorescence like dyes, so you can forget about maybe reflection is not as important as you can measure reflection You use proper calibration and you can say there's no other effects important there So you just say there's fluorescence and absorption and that's it but if you have fluorescence and absorption you will have the Heat not the heating effect there and then you just start you can measure what is being transmitted But the point is that the photo thermal method give you the energy used only for heating So you have the total energy that is lost and you have the energy that we use for heating you subtract You get the energy you use for fluorescence for example, and then you can estimate how much Energy are you using for fluorescence in relative to the energy absorb it how we call that quantum gel Quantum gel of fluorescence, or you can actually say quantum gel of thermal effects quantum gel of Photocoustic effect of whatever so you can actually invent all these parameters and so on I start Doing the characterization of your sample in such a way You define transmittance Well, yeah, he just has a division of that and first all these functions are Spectroscopy so they they depend on the wavelength of the incident line and they provide some information So the spectroscopy is a good method because of the same with the same experiment in one experiment We get a collection of Wavelength and we get a collect a big more global information about the properties of matter But here we have the transmittance and then we define absorbance This is the way for example the chemist they define they use the decimal logarithm and the physicist We like the natural logarithm But they mostly use in the spectrophotometers that what they have is the decimal logarithm of the transmittance. I would call that the absorbance Is unit less? There's no unit Sometimes some people put some units there, but there's no unit is a unit less all these magnitudes are without units And there are nice magnetism because they are easy to measure as you can repeat it And you should get the same information all time Reflectance you can measure the fluorescence You can collect all the fluorescence no you can collect all of that That's not that easy sometimes and you can measure the fluorescence and you can measure the photo thermal spectrum They call the energy use this photo thermal signal is proportional to that spectrum. You just divide over the power You are being used Here is the also that the discussion about the mod match mod mismatch This is a theoretical calculation using that theory We discussed in the first lecture the first correspond to when we have the probe and the pump beam with a Coupling parameter m close to one it means that there they have more or less the same volume Within the sample and we call that the modes the line modes are match Right there when you do that and then you do the so-called this can experiment You are scanning you have your light and you are scanning your sample around the waist of the light When you do that you get the z-scan Figure some people say that that this is not this can because you need to have care effect It doesn't matter so just you just you do care effect thermal effects It doesn't matter so any kind of effect can give you this can for thermal effects This is kind of the beginning if you have a negative The lens becomes positive at the beginning and then becomes negative The effect becomes positive at the beginning the lens is always the focus in but if you have the focus in lens before the focus in The regular effect is similar to having an increase of the intensity in the center of the beam at the far field But if you do behind the waist You will you will have that the focus is increased and then you will have a negative signal right there That's the reason you have this Z or Zoro signature, you know, but you have that I remember when I was a kid I like Zoro did something like that and Okay, this doesn't work. I cannot do my Zoro Okay, you see there was an interesting thing is that you have the positive Negatives in some in some place where you have the maximum this you get zero And that was confused a lot of people. Yeah, why you have zero when you have the maximum intensity, you know in this is can That is a little bit confusing. It's just a fraction effect. It's a diffraction effects can improve Or can reduce the efficiency of the system but when you use mod mismatch mod mismatch means that the Probe being is collimated It's absolutely collimated. So it's the same all For these different positions of the cell you are still scanning around the focal waist of the pump and You get the maximal response Whatever you have maximum intensity And of course if you have a negative lens you see immediately that is negative You have a positive lens you see that increases and it's very clear So there's no confusion with that It is just a Calculation of course when you do the calculation seems to be that they have the same signal No, actually the yeah in general. Yeah, but happens that the mod mismatch has more noise with the real life Produces more more noise about that. So this is what we have observed This is an experiments we did Very simple. So we have an excitation laser there could be yeah It could be a diode could be anything a lean laser and you have the probe laser. Usually I use a Hini 6 32 nanometers. I call me made that and I can just put some kind of another lens L3 It means I can remove that lens and put the lens So I'm going to focus or not or collimated I will have an experiment where I can switch from focusing the probe. Oh, thank you for focusing the probe Here I have this is my telescope right here. Then then you have this lens You can just remove if you remove you have the mode mismatch if you put back the lens You have the mode back just so you can do these experiments You just don't modify anything else and here you have your pump The pump is being focused over all the sample and then you have this point which is a beam splitter I usually use a wedge, you know the wedge is good because the wedge Eliminates any interference in the system because whenever you have interference you might have some vibrations there They're important. So I remove that just using a wedge right here So I just take one reflection from the probe, which is the only I need for that It's a it's a nice thing to do But usually you have in a regular microscope plate You will have some interference that makes a little bit messy the experiment But anyway when you focus there in your sample and then you scan your sample around the focal of the pump This filter is an interference filter that Cancel the pump light It's just in the leads all the pump light and then you have passing the probe can pass through and then you go into the Laptopature and then goes onto the detector for the detection system that you have So you only have as you move your sample You will see that the spreading because you have the focusing beam will be bigger at the bigger intensity And will be smaller far from the waist of the pump You have that one peak signature Here's the experiment so I can switch From one experiment for mode match for mode mismatch and that was made with just distilled water Just has to be you know water give you a good signal and I was able was able to I think I was using a little bit more power I don't know. I forgot to put the power here somewhere. I don't know I use a infrared which is good infrared is good because I water absorbs More or less okay in infrared 10 to minus two centimeters minus one and this is an infrared I just need to tiny sapphire laser as a good Power there and I get very nice picture as you can see the the signal is not that small as previous But still small still okay for the linear regime to work So if you have this signal to be close to one It means that the fact is to be and then you are losing it doesn't mean you are losing the signal It's just the lead the signal is no longer linearly proportional to absorption. It does it but the signal is still there and but it happens when you do an experiment anything with spectroscopy You for example, you have a light and you focus the light and there is some kind of waste And of course is when you do regular optics is this formula that shows you that way is the pain of the wavelength You use and this will be called the diffraction limit Fraction limit that you have you have you want to focus more you need to have smaller wavelengths So that means that was the people actually discover if you make it Blue lasers you can actually make this better and they spend a lot of work And that was finally the Japanese who did it. No, there's that was in the 90s They did the blue lasers today the blue lasers is a good achievement because you can use blue lasers diet blue lasers To do fluorescence to do excitation of molecules and to do a lot of things and the good thing there The cost has been reduced almost by to order of magnitude when you say you can buy a blue laser for $1,000 which is even less than that and that's impressive. That's that's a real revolution That's what we actually we okay now we have access to a low-price device We can we can do the experiments. We don't need to invest half a million or quarter million dollars to buy a laser to do that But the point is that this waste the pain of the wavelength if you change the wavelength The focal changes know the focal point That's the problem and when you do any focusing and you you have that in your optics You you may have a problem in the in the thing So usually you call me just to reduce this effect We still you have some acromatic behavior in your system and you can actually calculate your rally Parameter for the pump and you see that this rally parameter is just proportional You change the rally parameters is similar to changing the in my calculations You change the rally parameter in the calculations. You can actually is similar to change in the wavelength proportional to that Here you have a calculation May pay this theory that simple theory of the archotangent. So they have their tangents there Remember they are tangents. It has a maximum value of p pi over 2 You can achieve that when you have the mode mismatch experimental setup and You when you have that you have the focal rally parameter of 1 centimeter Which is give you probably 100 Microns or maybe 80 microns No of the in the spot and then you have a rally parameter of 10 centimeters You see the signal reduces a little bit, but we are changing the rally parameter 10 times And the good thing we're changing 10 times. It was still the signal is very close If we change 100 times, of course, it goes down But you spread over the system and here there's an excellent idea. Wow. Why we don't use Longer samples whether you don't use longer samples and then we have and we can have more More sensitive more more signal and we have an actual idea that with water I was able to build some cells of up to 2 meters with distilled water and there was measuring I did my z-scan with when I was focusing here You have when you use focusing a little bit less focusing a little bit less focusing very long focusing you have that almost flat And of course when you do the experiment and you do the easy your sample is very big You simply speak so you actually can get bigger signal if your sample is small It means if you change a little bit So there is no effect you change just you change your your Rally parameter by 20 percent Just a regular spectroscopy you go for 400 nanometers up to 700 nanometers You are changing about maybe 50 percent you change about 50 percent So you need to change about 100 times in order to see a change But if you are changing just below 100 percent the the effect is very low So if the chromaticity is reduced Essentially This is the experiment that shows that the signal grows Has the length is increasing and then I got an idea here. Oh, wow Why we don't use an optical fiber you want to put the light inside the optical fiber You put the probe you put the pump and you can do an experiment with the low power But you will see some changes. It's impressive. You will see some change at the end of the fiber You see because they accumulate over the length of that, you know now today you have this new technology called fiber lasers They just take advantage of the length of the fiber to produce more more non-linear effects You can do that sometimes five fibers, of course, they are to elaborate But in these experiments you don't need you can use any kind of fiber Any kind of fiber if you want to do in liquids you can use a capillary You can use a capillary for example, you have Teflon capillary It will confine it works like an optical fiber for water Because the water has in the refraction index of 1.3 and the capital and the Teflon has a refraction index of 1.25 something like that. So he acts confines because of the total reflection confines the light inside the capillary It means that you can actually work with liquids So if you don't have enough power if you just to take the little water liquid or water sample put in a big Capillary and then you should get the signal. It should be work or Do like Umberto is doing today. He's doing multi-pass. You can just do multi-pass system. He works. It will work as well Yes, you need to think a little bit about the optics a little bit more, but it works And you can actually increase and this is an experiment we did with the Titanium sapphire laser When I have access to this laser, you know this laser is very Expensive And I asked for a new laser. They go they want half a million dollars. I told you are crazy I'm gonna pay half a million dollars Who's gonna give you half a million dollars for doing that? It's very difficult to get that one unless you are I don't know Better rich you want to do it yourself? I mean the bill a billionaire something and you have When you do more the spectra you do the spectrum the two configurations I just said to the maximum of the in the mode match I just said to the maximum and start doing the my spectra and I see that in the beginning When I do the spectra the stars is the mode match in the beginning was fine That's the spectra of water and they and then when it goes goes low to the 700 the mode mismatch Give me some Little bit peak there, but if I do mode mismatch what I expect to have reduced chromaticity chromaticity, so you have And that this these are the the the circles right here the cross circles right here So I have that and this is say the water and the other black points that we have This is the measure of other people Using the absorption experiment the regular absorbance spectroscopy Which is difficult to do and they have published that in the infrared they have this This number is available in the infrared, so I just took from him from the internet I just compared for different authors that with my results and I see them what mismatch is good It gave you the same thing that you have with normal spectroscopy and absorption spectroscopy means that You have pure water probably Discovering in the infrared is very reduced So you should have the same result that you get from the absorption spectroscopy and that's a good calibration point There isn't something that is remarkable in this experiment is that this is a near infrared Experiment, but I use a visible light to detect the probing. I use a visible detector So I'm doing infrared spectroscopy, but I'm using a visible detector because I am detecting the probing and So some people are contacting me saying can I do that in the for microwave? Yeah Can I do that for UV? Sure? No problem Did you imagine you can do UV spectroscopy using visible technology and That's safe a lot of money too because these detectors in in the infrared sometimes a UV may be very very costly You can do infrared spectroscopy in any range of the infrared spectrum in any range of the electromagnetic Spectra, and you can just use the probing will be your visible technology Which is it's affordable and you can you know that very well, and you know you can evaluate You use the properties of your detector easily That's that's that's remarkable at that time. We didn't think about that I'm thinking about writing a paper about that, but you can take advantage and do some experiments And you will see this is absolutely new idea Yeah But when you do a spectroscopy here, for example, you have argon laser was a popular laser and The problem with this laser It breaks down You pay $100,000 and he breaks down in two years. It's very bad But it's still a very nice laser produces an excellent Gaussian beam and has different lines Here's the lines in the visible you have 454 This is by a little bit violent that you have this blue. This has a nice blue at 488. This is the very intense It's a nice blue. These are nice colors. Actually, you like colors. These are pure colors It's beautiful. Actually when you do experiments with argon and And here you have the the green light at 514.5 nanometers. These are the main Lines, but you can use all these lines and there are some lines in the UV There is even some lines in the infrared So this is a picture of your lines when you are working with the argon laser You probably have seen that a lot of times if you have sometimes the argon laser They combine all the lines together, but you can put a prism and you decompose all the lines that you can see that Here we did an experiment that was a collaboration with Brazilian They invited me to go and I showed you the method and they decided, okay Let's measure for water with the argon. They have an argon laser and they start measuring Okay, they have this one two three four about ten points We did that for the argon laser and we get the stars. We get that Here in 500 this is this is visible This is where you do not expect water to absorb and the absorption is you know It's ten to minus one ten to minus two meters. This is ten to minus four ten to minus five Centimeters it's very little small ten to minus five centimeters and talking about that right here ten to minus five centimeters Two ten to minus five centimeters. It's very small absorption. So you need it means that two ten to minus five centimeters You will need In one meter you have one hundred in ten meters you have one thousand ten meters to have some absorption there What but anyway? The point is that other people have measured that part and they get different results And we claim that this is because we are not measuring scattering and Indeed this these experiments were done in the regular absorption spectroscopy people use multi-pass systems Very complex what they call cavity ring down spectroscopy where they have the light passing passing multiple times through the sample and You actually get Maybe a kilometer of path when so they measure bad There is still some scattering and the scattering of course affects and they say why is so different? It's because different experiments you have different particles there and even water You know what there is a nasty solvent because the soul favorite thing even if you have the container There are atoms of the container dissolved in water. You have a pure water Long time in the glass container. You believe it's gonna be pure forever. It's not because because Particles contained in glass will be being attracted by water. You remember water is dipole and attracts everything and And gets something and suits who have purified water. It's so difficult with everybody working with real Experimenting pure water was that but we claim that you have this because we do not have a scattered I'm gonna show you that Actually people bought that paper and they were publishing the optics letter was a good was a good Journal has a lot of citations and the people actually called me because they wanted to put our numbers In some kind of reference because water is very important So everybody knows needs to know how is the absorption of water and they are actually they found that our Measurements are original and be well given some regular numbers and they know that they know that these numbers Has no coincidence. Of course when you go below the water who in the UV absorbs a lot it goes up very fast and This is the the the laser we use this is the laser you can use if you have it You are happy to have a Fantasy-second laser the Titanium sapphire laser you can use in the CW mood So you don't need to modulok laser and you have this spectra in the near infrared Which is an interesting region to do a spectra for the thermal spectroscopy has idea for water And here you have pumping with different Jacks because this is very just in the Odeon Jack. Lay everybody with some money can have a system like that But again this cost close to the half a million dollars Which is too much because you have to laser you have the birdie and you have the titanium sapphire that all the system And fancy stuff and just you plug bait Bottoms and you call technicians. They fix your laser for you. So you don't worry. I remember when I was today I was starting as a scientist. We have a dye laser. That was a pain I was forced to align this laser all time. That was what I Tried to follow the procedure recommended. That was real difficult to do But anyway Here's the spectrum water. We just provide that already. So we have these pope and fries the most famous people who have studied These are Scientists from Texas. They have this multipass system. I Make a lot of reference to them, but they never make a reference to me, but it's okay But at least we know that that's correct I use their numbers to calibrate my experiments to make sure that everything is fine And then you have ethanol here. I don't know has you know when you do ethanol in regular Spectrometer, you can have this red light right here has a good coincidence and here you have this is the carry This is a typical spectrophotometer commercial, but you cannot go below 900 You cannot go about about 900. You cannot go about 900 I still can go a little bit in the infrared here and get the peak Right here. So there's some disagreement here. So it is something to study why we have that disagreement. That's methanol ethanol Sorry, I did also other one methanol just a little bit different I have maybe a better coincidence. These are the photo thermals experiment and these are the carry absorbance against He cuts at 900 right there. So you can do a spectroscopy But what is the problem? Well, you need so much money for doing that. That's the problem And so the point is that? And we do just use a lamp Just use a lamp when I before we go to the lamp We just want to show one of our first experiment in the fluorescence dye We use rhodamine 6g is considering to be the best fluorescence dye and has a quantum yellow fluorescence over 90% and it means that almost all Photon energy is used for fluorescence, but still there is some energy used for Hitting for something. So we have fluorescence and heating So that simplifies a little bit the analysis and here we built this experiment We have a jack laser and then up parametric oscillator You just count that that's 100,000 colors and you hit you have that going here You focus then into the sample and here you just collect with the lens and you go here. You collect some fluorescence Right there. So we hope we call that excitation fluorescence spectroscopy So you just collect what is generated by all wavelengths that are being generated by different wavelengths of the laser It's called excitation fluorescence and then you have Detransmission of this light here you measure the transmission and v3 you measure the transmission Transpetance of the light so you do regular transmission spectroscopy and here you use a heaney That heaney goes into the sample together. Call me made it. I say you I don't use any optics here for the heaney So I use most with mismatch and then we go here and collect the photothermal experiment So we now we can tune our OPO. We can just select the different frequencies and start collecting a spectra That was done with collaboration with the Central University of Venezuela I think some of these people are I don't know. They're here or not, but we're previous collaborators students and Castillo was my student now and he's a good scientist. He's a good scientist back in Venezuela. He's still there And and there are other people that work in trying to survive there. It's okay Here you have What you have in the When you do a transmission and when you do fluorescence when you do fluorescence When you do what they call transmission experiment and you get this part with this What we call cross circles right here, so this is one minus the transmission This is something proportional to the absorbance if you happen a small absorbance So it's similar to the logarithm if the absorbance is a small And you have that and the solid line is the spectrophotometer is the regular spectrophotometer and spectra So we have for the transmission experiment because expected is the saying that the regular spectrophotometer Respected that no because we are doing a transmission experiment But fluorescence has some peaks here a little bit smaller here and that's the fluorescence the total fluorescence We call that we still bit calibrate with we really don't know the numbers But at the end I cut I will explain you how to calibrate this and this is the photothermal spectra In order to do the calibration. I just need to add this spectra to this spectra and I get The other this spectra and I get this spectrum You know the the cross circle so you have this is this this is the transmission and if I assume this over this I will get my I will get again my transmission spectra This means that I have split the energy the total energy into fluorescence and heating but there is a little bit of heating right here Still there is less than 10% in most of the frequencies that you use is less than 10% And it means that this is because it's very highly fluorescence died You have now you can use a quencher you can use a potassium iodine Right here's a quencher of fluorescence. So this means that fluorescence is not is a probability of fluorescence is smaller It's reduced it's called a quencher in chemistry. They call quencher this quenching of this effect Then you increase the probability now the energy need to go somewhere So it goes to the thermal effects now you have the fluorescence spectra reduce But now the thermal effects is bigger and again you assume then and you get your transmission Spectra your absorbance back so it means that you are splitting that and here we show that if you have a fluorescence sample The photo thermal spectroscopy is giving you something different. It's not the same It is the same if there is no fluorescence. There's only heating is the same But there is you have fluorescence. It's absolutely different. So this is another way of looking at Samples is another kind of spectroscopy. We did this work about 10 years ago something like that People don't reproduce because not not everybody has a diss system because it's very expensive experiment And you can define the fluorescence quantum gel this way and You can say that this is the average value of the fluorescence wavelength. You know the fluorescence is very wide roads You think the average value of the wavelength. This is the use wavelength. This is the absorbance. This is the thermal effects Signal, this is thermal signal. This is the transmission, which is the absorbance. This is 1 minus T This is the absorbance and you get that this is provides you the probability that the Energy will be used for fluorescence. It's called the quantum gel of fluorescence, and it's very big It's about I think I measure that here. You see here depend on the when no quencher You see sometimes it's close to one, but it has some peaks has some structure so what the beautiful thing now we are getting the Some kind of total spectroscopy of fluorescence, but in another way we are making another characterization Now we have the quantum gel of the system for has an spectra and that was possible because of the photo thermo See if you would use the quencher you can actually damage Not reduce substantially this quantum gel and you got this below a noisy a little bit Okay, now it's the point. Okay. That's this is not business that we have big lasers to do that and We were thinking okay. Let's try to use a lamp and we have the arc lamp. This is a nice Source of light very common because producing the visible is more or less flat and it has a good infrared tool as a lot of Picks in the infrared and it has some UV peaks So whatever you work with this lamp and you can it's good if you can filter that UV because it's not good I use water. I just use my big cells of water has a filter just to clean the light From from UV and be sure that there's no UV There so my students can work safely And I can work safely and then I just focus a little bit into system of filters I have what they call a variable filter, but I discovered this filter or better to save the filter From the debacle what do we have and then we have this filter right here But they just both build the filters right now So you can beat build filters, but that's probably the most expensive part You want you can buy a filter for every 10 nanometers You can have from 400 up to 700 about 40 filters or 40 and 5 you can do infrared filters too as well You can buy more filters and maybe it's around $5,000 investment to get all the collection of filters good filters So or you can use a monochromator and to do that the problem with the monochromator. It reduces the power You still need some power. So I use these filters because I saved a little bit. I was able to get about Several I think half a milliwatts in the blue something about half a milliwatts in the green something about about that half a milliwatts from the lamp Half a milliwatts 500 micro watts about that. That was good enough to do in the experiment So you can say half a milliwatts can you do for the thermal linear of this with half a milliwatts That was something Inexpected but now you have seen the experiment though from birth that you can do it for the thermal spectroscopy with two million What two milliwatts one milliwatts you can make it with a lamp and tell you you can do with the lamp and today They are good lamps actually and Some people forgot about this technology. They believe the laser is going to replace that but you know These are they want you to pay more money, but you just get the lamp That's a good sign. You have your lab. You have a lamp. That's a good thing It's a good source of light and then you have your filter here you have on a chromatic light you can just start doing this and You focus that light here And you have the probe here collimated You can actually see just a small changes in the focal points here do not affect substantially. It's because of the collimation Because of the collimation of the probe so it doesn't feel that and you know that the The size of the thermal lens is not being affected substantially for that Within the visible range and then you can do the spectrum start pushing your system. I repeated this experiment with Repeat the experiment with Malakit green which is a non fluorescent dye Malakit green is used in biology to that dye some cells and see some organelles inside the cell But because they die differently. They have some contrast and the Malakit green We have that dye and we did this is the spectrophotometer normal spectrophotometer. This is thermal lensing With the Malakit green and it has these two peaks right here. It's perfect perfect coincidence no perfect coincidence between and Thermal lensing and that that's a good calibration of your experiment now You know how much is your signal is just the the absorption you can use the absorption to calibrate the photo thermal experiment in this case, no and But if you use You can actually die that has fluorescence like the Rodham in 6g and you see the now the photo thermal experiment is completely Different from this is the absorption and this is the photo thermal You just normalize that here But just to show that the contrast that they are different in magnitude But also I show that there is something different there and using now instead of a laser a lamp that was there was remarkable about this paper is It's just that you can perform that with the low price with the low cost for your lab or other and This is the quantum gel I got I was able to do from 400 things similar to the quantum gel Obtain it before it's not exactly the same because the concentrations were a little bit different things There was not exactly the same sample and we did that in different times actually these experiments were not at the same time But you have the definition of the quantum gel fluorescence and how you do that? So some people in chemistry is very important to know that You want to characterize a die? You need to know the quantum gel fluorescence for that and that's the regular is regularly Added into the table of description of the die But I have never seen a spectrum of the quantum gel fluorescence And this is the first spectrum actually the quantum gel fluorescence You can actually provide the more a better information a better characterization for your sample That's another experiment done also with why light and this is about scattering samples So turbid samples and you have Malakit green again. This is Malakit green. I repeated the experiment again I get a very nice coincidence and I use now What they call plastic micro spheres latex micro spheres About one micron size and added there and start increasing the Scattering when you increase the scattering the absorbance of course becomes bigger You can actually can see here. The absorbance is bigger, but for the thermal is not affected The photo thermal spectra still reproduced the same thing I used to have But this is done with the sample that has a lot of scattering So it means that the scattering sample because in the transmission experiment you are measuring two things You are measuring the losses due to heating and the losses due to scattering But if you have photo thermal you measure only the losses due to heating And then you can combine them a maintenance copper and spectra And this is metal in blue. That's another dye. Just you is also not fluorescence dye Floresce a little bit, but not too much Almost 90% is heating and you have For different concentrations on these micro spheres, so it was adding a lot micro spheres here. You have You say zero so you get my spectra right here. They are added a little bit more They added that a little bit more you add there it becomes milky because very milky I still get the signal I still get the signal because like milk No milky very turbid system, but still you can do spectroscopy So it means that you have a sample of water, which is Taken from the river or taken from Anywhere you don't need to purify you just do and because you may see in the purification method You can change a little bit your sample you want to take your sample as it is and then you do this spectroscopy You are sure to measure only the absorption View to heat it and that will be done That means that this is what you should obtain without turbidity without this all this particle that you have in your sample of water And that's interesting thing to an interesting application for a spectroscopy for this kind of a spectroscopy And then I was able to do I was able to do Okay Fine I was able to do the scattering spectra. This is for Malakit green You have some peaks and you have this captain is big in this and interesting why? No I still Know why it is happening, but happily the referee didn't ask me and it got published But the point is that it's interesting. It's just interesting why this is happening It's something to think about what you have this captain is bigger here and smaller here bigger here You have some peaks on the placions and that happens because scattering probability also changes when you have the wavelengths You change the wavelength you have certain response that changes So we usually don't think that scattering has something that changes with the wavelength, but it changes with the way Why? Because the refraction index changes with the wavelength So you have this particle they have different diffraction indexes and they will have different scattering So that will be cool to just to make a model how the scattering changes when you have different refraction indexes And people do this kind of calculations with the meta materials We have meta materials nanoparticles and they see this copper up today you use console Programs to calculate the electromagnetic field generated. We have done something like that Actually a cool thing thing we did recently and have a collaboration with the mathematician and he was it he has a program that calculates the In two dimensions the electromagnetic field and he was showing that the scattering field depends to the Coop of the radius of the sphere of the nanoparticle, but the photo thermal depend No, the scattering depend to the the square of the volume to the square of the volume But the photo thermal depend on the volume and then if you increase the particles You have a big particle you have big scattering you have small particle you have small scattering We did that recently in other work. We did that. That's interesting people who study scattering Most of the difficulty with scattering is that it's not generally easy experiment to do But now we're providing a new way of doing this experiment That's for me to leave blue And that's gold nanoparticles I use gold nanoparticles The solid line is absorption for the Commercial spectrophotometer normal transmission absorption they have there and be the this big this in circles are for the thermal I you see a good a good coincidence. It means that gold is Has the lowest scattering at least for this size of nanoparticle as a big absorption And I was able to because you know gold nanoparticles They are you have a golden particle here 15 nanometers You can calculate how many atoms you can calculate what is the concentration the molar concentration of nanoparticles and then to the nanoparticles You get this extinction coefficient right here 10 to 11 and we go back we compare with dyes. I Don't know if I put somewhere Extinction coefficient of malachite greens 10 to 5 and 1 million times bigger 1 million times way why? Because we have a lot of atoms nanoparticles. You have it's not one molecule is with a lot of atoms of the nanoparticles They very effective in concentration of heat It means that the following that nanoparticles are these nanoparticles are It nanobombs You can focus then and you've localized the heat in a very small point People are using that for killing cancer killing bacteria killing anything For for example, there's an interesting experiment that you have bacteria today You know the bacteria there they evolve and they you have antibiotics so they become resistance to antibiotics There is a problem with tuberculosis because tuberculosis is very easy to transmit It's just through air and and it's dangerous. You die up to work from tuberculosis you use in the past people die a lot from tuberculosis and And people are careful about that because they know very well this well now the bacteria It's resistant How you kill that so you can add some nanoparticles and then you illuminate with the laser explodes Because people have reported that you have the nanoparticles you generate locally and you generate nano bubbles Very small bubbles because the temperatures are very high locally Really, it's like a bomb that you have so we don't see that like a bomb because it doesn't explode No, in your laboratory, but locally is making a nano explosions and you have that but you can use that as an Sculptor and that's what people are thinking about doing this Some some applications in biology that you have and that's the scapula in spectra That's this is gold and this is blood Don't think this is not the blood of my students. This is the blood from the chicken I got from the nearby store and just go that you take that blood and put in my in my sample It should be in jail if I take the blood of my students They can put me in jail Cannot do that. But anyway, you do blood and you do absorption spectroscopy The absorption is normal with the normal spectrophotometer. You get this peak That this way you do with photo thermal you get very very different thing and Then you have these peaks in this category So you can do a new kind of analysis of blood. You don't need to remove the blood cells You can do it because it for the sample has it is and you can now develop a new kind of applications for blood analysis Which is very very important You know that this is a multi-billion dollars industry and you have And recently that was a problem with the company called tyrannous That they invented the way you can do it when they you do the blood work They take at least 20 milliliters. How you some people are afraid people this may But anyway, it's not nice take a people don't some people don't like that But here in there they claim that you can use a small drop of blood to do the full analysis and The complaints against that was the the noise they say that because you do have enough sample in the noise is very big But this kind of approach could be give you A new idea has to survive just work with the small drop of blood Just taking for the small as you do every day for blood for sugar checking Not a lot of blood just a little bit to do the full analysis Maybe you can do that and now you have a new way of some kind of new Spectroscopy you can do a scattering spectroscopy of that's blood samples and of course blood samples. They are different and you have You can actually Take your blood and you see this is normal blood. This is blood with sickle cells, you know sickle cells They have different shape Because of the different shape the scattering is very different So the spectra for sickles blood with this disease should be different from the normal blood Or maybe it's different. It's not the same check and that people maybe I didn't do that But it just showed the method no it's interesting that Just to finalize and talk a few words about something which is also interesting is to do a spectroscopy Okay, we can work with the lamp and We can can we do that in reflection? Can we do a thermal mirror with that? And and again the thermal mirror is something like that We have the light coming into your sample you produce some Some kind of nano distortion there in your surface of the sample and then you can Test this with the probly beam and analyze what is happening there So we have done that in this experiment with the lamp right here at this lamp and we have On the filters again, and we have our Hini for the probe here. We focus the view the This is a light from the lamp here We focus in that sample that produces some bump there, which is very small and then the point is do you have enough power? to produce a signal is the signal good enough so and Actually, it's very similar to the photo thermal lens, but instead of Doing in transmission you'll do it in reflection and you can do different configurations and you can start inventing Maybe you can just several times you can send the reflection there and see if you can improve your your result a lot and Here you can define your signal again. This is the transmitted probe Measure by the detector through that aperture When you have the thermal effects and here when you do not have the thermal effects This is what you do. You are chopping your beam. You're having you have the light You don't have the line you have the light at some frequency I usually use a low frequency because to give because when you call it made the beam You need to give time for the for the built up of the thermal effects So you just use one hers, maybe half a hers, but I think I was able to do two hers right here The bad thing about that is that if you do too slow, you need to wait too long And so you need to be passionate, but here you can actually two hers is still okay But you have the signal of course is proportional to this quantum gel of heating I mean, this is the probability that the absorbent energy will be used for heat and This is a coefficient that depends on the geometry of your experiment You can use just a calibration factor or something and that's the power of the light So usually you want to calculate this you take your signal you divide over the power For each wavelength something you get your spectra And this is what they call this five capital five here Greek. It's a PTM spectrum What do you call that? Yeah, I have a PTM this is the absorbance of a I take a dark With the very low transmission filter is used to reduce the power of lasers and things and And they have this glass plate and I have the absorbance. I was able to measure the absorbance because it's Very big That's the absorb of the filter filter has about few Few millimeters when you send absorbance of six, you're close to the limit of the device Which is 10 so you cannot measure more than 10 in the regular devices. This is very big Usually you work with absorbance below one But he has very big absorbance and he this is the signal I get from the photo thermal mirror for the thermal mirror experiment and it helps two peaks and I still didn't publish this I'm still thinking still thinking why we have these peaks and things like that and Here you have a film of silver It's a plate of silk nanoparticles of silver Made they have some people doing this kind of materials. They do that for possible Solar applications or silver, you know when you see silver is so dark Absorbs everything is very dark and and you can of course you cannot do transmission That's very difficult to do transmission with that, but you can do reflection I think got the spectrum that resembles the spectrum of silver Which is very cool that you get still noisy, but still you have three peaks there And they say that these peaks are because you have this photonic peak and then you have some conglomerates of nanoparticles They put together and they have another photonic peak right here, and then you have another bigger Conglomerate and you have another photonic peak right here So that's what more or less the explanation of this peak So this is a good a good thing to do and then I have a collaboration with some people who does nuclear materials And this is the material is called this prosion titanate this prosion titanate is a material You know is used the element this prosion is not it's not common element, but the good thing is that it's a It is just a mineral and it's nice You can polish that you get a good reflectance surface and The interesting thing is you got more or less flat It means that it doesn't change here for this wavelength here, but then suddenly you have some drop And I'm thinking where the energy is being used for it means that something else is happening in that sample Maybe we are generating some because I don't see anything. I don't see anything It's not easy to see maybe we are generating some carriers Maybe we are just because it's also has some semiconductor properties Maybe you're generating some some current and this current is there Maybe you're charging that so you need to to go forward so the energy is doing something So now I have any there. Let's see to see we can see the photo effects from metals The photo effects from metals because but I am working on that right now It's just to see with this technique, but we just need to increase a little bit the sensitivity And that should work with can you do that with the laser sure But again if you have the money is fine don't have the money is not good, but you can do with the laser work will work perfectly It will work perfectly. You have this continuing laser, but right now I do not have Sometimes you have access to the laser sometimes you don't have access to laser and but you have access to a laser Just do the experiment that will be cool and I ensure that you can make some get some results and gets published for that Because it's absolutely original so here with we make a conclusion is that for the thermal spectroscopy is it's a new way I hope I have convinced you is not the regular spectroscopy is something new and there is no devices commercially available Maybe we can shoot start a company and start doing something like that No, but I don't know it's something risky. No, sometimes you don't know you need money to do that But there is no commercial device. Maybe it will be commercial device maybe the next 20 years or something like that But this is something that probably will be used because has a lot I see there's a lot of implications and a lot of applications for characterization of materials So, okay, so I just wanted to show a little bit of the advantages of the spectroscopy Just to say that first is sensitive very sensitive convinced that it's universal It happens for any time it gasses any sample doesn't matter Scattern fluorescence free. That's another advantage only visible sense doesn't important advance only visible sensor technology required So you don't need UV technology you don't need infrared sensors and people are contacting me from Florida because they use a medical quantum cascade lasers to do middle infrared spectroscopy Which is important for calculating measurement of pollution pollution in atmosphere so they measure that the different gases in infrared spectroscopy They use a cascade laser we can scan about one micron something like that in between two and three and four microns that's the middle infrared And they can do this spectroscopy without thinking because these detectors you know they also depend strongly on the wavelength But here you don't worry about that because you are detecting at the fixed frequency in the visible the detector is the sample itself So the sample is the detector the potential detectors the sample Almost finished and you can do you can do that remotely you can do this spectroscopy from some distance It's like ramen you know people do ramen from some distance and some people have some applications you have an enemy who wants to explode me as I just from the distance see the bomb is approaching and then I kill him first You know before he kills me something like that you know people like you know in America they have interest on this kind of projects but we're thinking it's bad yeah but it's reality you know you can do anything And then then you have traditional and modern life sources technology can be adapted and what I think is the most important affordable it is affordable and there's no sooner or later we're going to have to do commercial device It's very affordable and when they appear they want you to charge $50,000 this is what is going to happen with the big companies will develop things like that But you can do it yourself now you can just discuss a little bit about life sources just before I finish is this is the arc land this is the more more popular this is Shannon you have the spectrum of the Shannon It has very flat indivisible it's nice of course a little bit of UV a little bit right here but in infrared is fine you can do infrared spectroscopy you can but I need to buy my filters for the infrared Which is interesting this near infrared spectroscopy the lab so you have almost 1100 nanometers which is almost close to the middle infrared This is another kind of lamps you have to mercury you can compare this is the Shannon here you show that Shannon is the best because these other lamps they may have some big lines there but sometimes it's not you want a little bit flat It's the flat source this is the lamp commercialized by Newport it has a very big intensity but you can see the price that's a 22 for a lamp wow that's a lot of money You probably can find you can find a lamp forgotten somewhere in the lab so somebody used that they remember when I was in Venezuela somebody was working and they gave me the lamp they actually inherited somebody left that lamp forgotten for 20 years And then because it's an old very old technology and the lamp worked perfectly and I was very happy was able to do the experiment because I didn't buy the lamp the lamp was there for somebody else bought for me before So maybe if you are in the lab if the lab has some history maybe you have some forgotten lamp somewhere just I suggest you to look around and see if you can find a lamp Instead of paying 20 but you have money it's fine that's an excellent device it's cool and it has this you can put in a monochromator and it's automatic you can regulate One thing you need to tell I do that by hand point by point with my hands I have my I do it myself and they get so back pain but my students also get tired it's a lot of work doing point by point by point You need to do it with the scanning with the electronically and then it will be fine will be fast fast enough That's that's the best thing I think but look at the price $10 a lot of power you can have 100 watts of light and the problem how to focus that how to do that and put inside and focus on to use this light But this is probably the future why because of this no it doesn't cost anything you can buy it yourself you can go and there's no UV And they're very well characterized spectrum the visible here you have 700 there are different kind of let's you have let's an infrared let's in UV let's the people are developing this let's very fast and the good thing about let's Is the price is the best thing that we have and still what is funny is that the Edison lamp survive for more than 100 years and the idea of the land was so good that is used to represent the idea of idea No the lamp Edison lamp that lamp the problem there and then you have now to the LEDs people try to replace the Edison lamp because it's not that efficient but they want you to pay a lot of money I don't understand that because this let's are a lot cheaper than the Edison lamp but this is a question of commercialization The commercialized trying you to pay eventually in the market the price will settle down and the lamps will be very very affordable because you just need to pay I think no more than one cent for a lamp like that doesn't cost nothing because actually nothing you have it's mostly the technology that you have your pain for the invention mostly No but this is very promising device I got one but it gets very hot very fast I need to cool down there's some trouble but it's promising That's the argon laser you have you're happy to have an argon laser it's a beautiful laser and you can buy or maybe you inherit that don't drop it just keep it try to keep the problem with the argon laser you need to have water cooling system and you have usually this water should be clean and that's the problem over some years they break down but these are more or less the lines of laser You have the infant second but this is the meter laser it costs a lot of money and you have these tunable lasers tunable lasers diode diode tunable lasers a new way of doing this is the tuning wave you have 830 to 870 here you can do some spectroscopy right here and the good thing about that is the power and the good thing also about that there's a lot of companies making that so there's a lot of competition so you maybe you can get a good price I know Chinese are experts and you have you want to have some tips about how to buy cheap lasers just Google Chinese lasers and you will see that will appear some different companies CNI is one company or other is laser brand I just buy lasers from them because I got sick of buying thousands of dollars I pay then 200 dollars for a jack laser that's nothing that's really good people say no it's not the best laser yeah but it's 200 dollars it's good enough for doing the experiment this is another tunable diode more expensive it goes from the middle infrared 1500 you know this region is very well done because it's used for telecommunications and that's very well developed it's used for doing the signal processing internet everything is going through these wavelengths and this is this is another invention which is you know this is the super continuum you have fan second laser of enough intensity you just focus the laser on water immediately you will see why light what is happening is dispersion so you have the dispersion of the fan second pulse because the fan second pulse is very unstable and you know the fan second pulse is formed it has a spectral width maybe of 10 nanometers you can actually start if you have dispersed medium you can disperse then and get a very wide spectrum you get a very wide spectrum you have some fantasy come produce this for example this is one company called NK photonics they produce this laser which is excellent and I ask them for a quote and they say 100,000 I say okay too much but anyway that's the idea I think one thing so we need to conclude here is that for the thermal spectroscopy is something that has been there for a while people have confused a for the thermal spectroscopy with a regular absorption spectroscopy and that maybe is the reason people have not developed yet the device the commercial device for doing that people are doing something but still in the first stages the first point the first development that we have eventually I guess we're going to have some commercial devices maybe affordable prices maybe Chinese will make it very cheap and we can get from them or maybe we can build ourselves maybe we can build and develop these companies ourselves so I just wanted to see that when I was like you 32 years ago like here being a young scientist absolutely confused about life with no don't know what to do and things like that and and and I got again when came here we met a Abdul Salam he was alive at that time was a bright guy and actually inspired that's a good thank you.