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The First year of my Ph.D - What i did other than being lazy - Krishnakumar Chullipalliyalil
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- 3. Photography + refrigeration • refrigerator = = cryo- cooler + • Photography = = spectroscopy 3
- 5. Light atom Hot atom Light atom cold atom Stokes fluorescence Anti-Stokes fluorescence energy energy 5
- 6. Excited state Thermalisation Pump photon Anti-Stokes photon Ground state Solution containing fluorescing molecules 6
- 7. FLUORESCENCE SPECTROSCOPY More interested in photography rather than the fridge :p Mission: Get as many as anti-Stokes fluorescence spectra as possible for 3 dyes (Rhodamine 101, Rhodamine 6G, Rhodamine B) Under different conditions of temperature, concentration, intensity and polarization. 7
- 9. Simple optical instrumentation-Schematic Achromatic lenses He-Ne Laser CCD Mirror 1 Mirror 2 Monochromator Cuvette Cryostat Optical Fiber 633 nm, 1mW Fluorescence 9
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- 11. FIRST SET OF ANTI-STOKES FLOURESCENCE SPECTRA (a) Absorption spectrum of HTS - Rh 101 1.2 1.0 0.8 0.6 0.4 0.2 0.0 HTS - Rh101 400 450 500 550 600 650 Normalized Absorption Wavelength / nm Excitation wavelength 600 500 400 300 200 100 0 (b) Temperature dependent spectra HTS – Rh 101 700 600 500 400 300 200 100 Intensity at 590 nm exponential fit − 3.70 3.90 4.10 4.30 4.50 4.70 4.90 5.10 5.30 5.50 Intensity 103/Temperature / (1 / K) ΔE= 2.402×10-20 J = hc 1212 cm-1 1Energy difference reported = 1262 cm- 푰 = 푨풆 Δ푬 풌풃푻 Temperature Calibration ! 0 550 580 610 640 670 Intensity / counts Wavelength / nm 294 k 279 k 244 k 218 k 199 k 170 k 151 k 135 k 128 k Excitation wavelength Krishnakumar Chullipalliyalil, Albert . A. Ruth, Atul Thorat, Michael. A. Morris , “ Dependence on temperature and concentration of anti- Stokes fluorescence from rhodamine 101 on silica nano particle support.” Conference on analytical sciences - CASi, UCC, Ireland, 1-2 July, 2013. 11
- 12. CONCLUSION 6 samples under 4 different conditions like temperature, concentration, polarization ( beam property), wavelength ( beam property) almost 24 spectra were obtained Moral: Good food habits always helps you ;) 12
- 13. ACKNOWLEDGEMENT Dr. Andy Ruth, Dr. Sophie Dixneuf, Dr. Ranjini Raghunandanan 13
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Editor's Notes
- As a kid I had always wondered what I would become. The greatest passion I had when I was a kid like when I was 3-4 years old was to become a bus driver ! (I dunno why ). At a later stage I thought I will end up may be in some shop where I have to deal with the customers. And at a later stage engineer etc etc. But none of these had to do any thing with my passions. I have two main passions. Ofcourse I like photography. I always wanted to be one good photographer, but have only managed to become an average one till now. The other “passion” that I have is sneaking in the fridge in the mid night for food !!! :D :D I just love doing it :D :D I love both these instruments. It is like I am married to a camera and I am having an extra marital affair with the fridge :D :D Jokes apart, these are the two things that I like.
- So when I chose a PhD, I chose a combination of both !! Both in the sense, not photography and food, but photography and refrigeration !! :p :p The refrigeration I refer here is cryo cooler – temperatures below to -150 degree celcius or 123 kelvin. And the photography I refer here is spectroscopy.
- What if I say that I can cool this wall just by pointing this laser ?? Well frankly speaking, that’s just being stupid. Nothing that fancy is going to happen in the near future. But, you can of course cool if you have a laser of enough power and if the mass you are trying to cool is small may be like this- That’s what you call a typical “selfie with a sample” :p :p Think of the advantages here- you are a beam of light to cool – no hard machinery, nothing ! You are attaining cryogenic temperatures ! This is possibly the only technique known to cool solids using light !!
- Now how does this work ? The technique is pretty much simple. We all know that each substance absorb and emit light radiations which we normally call as flourescence. Usually if light is incident on some surface, some part of it is absorbed. It keeps some energy within , and emits a part of the energy absorbed , which we see as a different colour – like the party UV glow things that you see. There are also materials which do the opposite. You glow some light on it, it absorbs light, and releases its energy as well along with it !! If you actually decrease the energy of any system, you are infact reducing the temperature of the system- or you are cooling it !! You might ask, what if at some point the energy of this thing loses completely ? That’s when it starts absorbing enrgy from its surroundings and will eventually cool anything in contact with it. We use lasers for cooling and hence this technique is known as fluorescence laser cooling.
- So what I deal with in my PhD is not actually cooling, but as stated before, taking photographs of these cryogenic process – How can I do that ? I told you before, the particular target material emits light, which is typically characteristic of the material. If we can capture the light that is coming out, we can search for a lot of things like- what exact temperature is it in, what kind of light will be perfect for making it cool further, what conditions should you apply. Capturing of that light- just like a photograph on a wavelength scale is what we call as a spectrum. So my job is basically to capture this light and record the spectrum. This is not as easy as it seems. We need to develop an optical set up for this.
- In our lab, we basically develop new experimental set ups for spectroscopy. This was what I did for my first year. This is what you call an optical schematic of the simplest set up to study an emission. You basically need a light source, a sample and a detector. The complexities of the system varies on the level of difficulty in achieving a spectrum. Here I have a laser as the source, the sample a monochromator and a CCD camera for the detection. There are loads of design considerations here : like starting from the source. Picking the right wavelength, accurate alignment of the beam and other optical elements etc. The chamber holding the cuvette also needs special attention, we should not detect any external light rather than the emitted light, so a dark chamber might help. The sample taken in liquid form is always easy to analyze. Here is a liquid sample. I had studied 6 samples under 4 different conditions like temperature, concentration, polarisation ( beam property), wavelength ( beam property) which makes it around 24 different spectra for the dye samples alone. Each one of them provides valuable information regarding the process.
- And this is what it will look like in real now :p :p !! As you can see its quite boring to explain it. That table is what you call an optical table, you can find it in all free space optics labs. The figure shows only the excitation part, the detection part is never shown. As you can see it runs from one end of the table to another. And what you can see at the other end of my table is some set up which is more exciting which I might explain to you in some other time :p :p Don’t worry, I am not going to explain it to you now, I can see loads of sleepy heads already, but any one interested can come to me in person and I will explain it to you !! :D :D
- Well, here it goes all complex now :p Its for all of ya studious people. :p :p I had studied 3-4 different dyes in my first year which can emit anti- Stokes flourescence with high efficiency. The sample here is dye attached to a silica nano particle and checked for emission.
- 6 samples under 4 different conditions like temperature, concentration, polarisation ( beam property), wavelength ( beam property) which makes it around 24 different spectra for the dye samples alone. These spectra gives enough information about the new system in terms of cooling.
- I would like to thank my supervisor and my group members for all their support. This is my group as it is now. I would also like to thank my funding agencies…. And those few gods of internet without which none can live now a days.
- When I started my presentation, I started talking about want I wanted and whom I wanted to become. I kind of know the answers now I guess. What I wanted ? I wanted to be happy. Whom I wanted to be ? I always want to be ME. Thank you !