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Lasers! What are they good for?

Lasers! What are they good for?. Applications in Biology and Chemistry Kevin Schultz Dept. of Physics and Astronomy APSU. My Background. Trained in atomic physics. Atomic hydrogen good. All else Bad! Moving on… $500k to build a lab to study the optical properties of photovoltaics

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Lasers! What are they good for?

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  1. Lasers! What are they good for? Applications in Biology and Chemistry Kevin Schultz Dept. of Physics and Astronomy APSU

  2. My Background • Trained in atomic physics. • Atomic hydrogen good. • All else Bad! • Moving on… $500k to build a lab to study the optical properties of photovoltaics • Many of the instruments can be used for chemistry and biology • So… make a user facility!

  3. a few, uh, provisos… A couple of quid pro quo. • I am not a chemist • I am not a biologist • I have never performed any of these experiments • I would like to though...

  4. Lasers Spontaneous Emission Stimulated Emission Absorption • Monochromatic… Usually • Line-widths of ~30GHz can be obtained (<1cm-1) .Less than many atomic transitions. • Wavelength stability to better than 1 part in 108 • Coherent • Spectrally bright. Lots of photons can be imaged on a sample (some lasers are 1020 times brighter than the sun!) • Directional • Makes interferometric techniques easier

  5. Spectroscopy • Absorption Spectrum given by • ΔI(λ)=Io(λ)-IT(λ) • Advantages of Laser Spectroscopy • No need for a monochromator • Resolution limited only be the absorbing molecular transitions • Detection sensitivity increases with increasing spectral resolution • Long absorption cells can be used Example: a 1m spectrograph has ~0.01nm resolution corresponding to Δν=12GHz at λ=500nm Doppler Width of a molecule at room temperature ~1GHz Single mode lasers have resolutions sub-kHz->ΔI/I 12 times larger than conventional absorption spectroscopy! Image from: Demtroder. Laser Spectroscopy

  6. Lasers in Spectroscopy Image from: Demtroder. Laser Spectroscopy

  7. Cavity Ring Down Spectroscopy • Assume a cavity with two mirrors with reflectivity R • The transmission of the mirror is then • T=1-R-A<<1, where A includes other losses • After a time t the detected power will be • P(t)=P1exp(-t/τ1) • The decay times with and without the sample are measured and it can be shown: • αL=(1-R)Δτ/τ1 • Let R=99.99%, Δτ/τ1=10-4 αL=10-8 • For L=1m α=10-10cm-1 Image from: Demtroder. Laser Spectroscopy

  8. Fluorescence I Images from Lakowicz, Principles of Fluorescence Spectroscopy

  9. Laser Induced Fluorescence • Advantages: • Single excitation makes a simpler spectrum and thus easier level identification • Stronger excitation levels, allows for detection of transitions with small Franck-Condon Factors • High sensitivity allows reconstruction of potential curves • Can determine population distributions • Level spacings of polyatomic molecules show signatures of chaos. Images from: Demtroder. Laser Spectroscopy

  10. Non-linear Spectroscopy

  11. Saturation Spectroscopy

  12. Laser Raman Spectroscopy • Lasers are an improvement for Raman Spectroscopy • Fluorescence minimized • Overcomes weak Raman effect • Used in Analytic Chemistry • Surface studies • FT-Raman similar to FTIR • Raman microscopy possible Images: McCreery, Raman Spectroscopy for Chemical Analysis

  13. Time Resolved Methods

  14. Time-resolved FluorescenceTime Domain Images from Lakowicz, Principles of Fluorescence Spectroscopy

  15. Time-resolved FluorescenceFrequency Domain Images from Lakowicz, Principles of Fluorescence Spectroscopy

  16. Time-resolved Fluorescence Time Domain Lifetime Measurement Frequency Domain Lifetime Measurement Images from Lakowicz, Principles of Fluorescence Spectroscopy

  17. Pump-Probe Spectroscopy Images: Lutz, et.alPNAS, vol. 98, 962—967, 2001

  18. Multiphoton Microscopy

  19. Multi-photon Microscopy II Handbook of biomedical nonlinear optical microscopy‬ By Barry R. Masters, Peter T. C. So

  20. Confocal Microscopy Wikimedia: Diaspro, Bianchini, Vicidomini, Faretta, Ramoino and Usai

  21. Optical Coherence Spectroscopy medOCT group, Center of biomedical Engineering and Physics, Medical University Vienna

  22. Stuff I Left Out • Ionization Spectroscopy • Two-Photon Ionization Spectroscopy • Optogalvanic Spectroscopy • Photoacoustic Spectroscopy • Velocity Modulation Spectroscopy • Laser Magnetic Resonance and Stark Spectroscopy • Polarization Spectroscopy • Saturated Interference Spectroscopy • Doppler Free MultiphotonSpectoscopy • Doppler Free Laser-InucedDichroism and Birefringence • Hetrodyne Polarization Spectroscopy • Stimulated Raman Scattering • Coherent Anti Stokes Raman Spectoscopy (CARS) • Resonant CARS • Hi Anna • BOX-CARS • Hyper-Raman Effect • Firckin’ lasers • Resonance Raman Effect • Time-Resolved Raman Spectroscopy • Laser Spectroscopy of Molecular Beams • Cluster Spectroscopy • Nonlinear spectroscopy in Molecular beamsLaser Spectroscopy of Fast Ion Beams • Spectroscopy of Radioactive Elements • Photofragmentation Spectroscopy • Laser Photodetachment Spectroscopy • Mass Spectrometry • Optical Pumping • XKCD • Laser Spectroscopy of Fast Ion Beams • Spectroscopy of Radioactive Elements • Photofragmentation Spectroscopy • Laser Spectroscopy of Fast Ion Beams • Spectroscopy of Radioactive Elements • Photofragmentation Spectroscopy • Laser Photodetachment Spectroscopy • Mass Spectrometry • Laser Spectroscopy of Fast Ion Beams • Spectroscopy of Radioactive Elements • Photofragmentation Spectroscopy • LaserPhotodetachment Spectroscopy • Mass Spectrometry • Optical Pumping • Laser-RF Double Resonance Spectroscopy • Laser-microwave Double Resonance Spectroscopy • Optical-Optical Double Resonance Spectroscopy • Bored yet • Triple Resonance Spectroscopy • OODR Polarization Spectroscopy • Hole-burning and Ion-Dip Double-Resonance Spectroscopy • Level-crossing Spectroscopy • Quantum Beat Spectroscopy • Excitation and Detection of wave-packets • Photon Echoes • Optical Free-induction Decay • Heterodyne Spectroscopy • Correlation Spectroscopy • Single-molecule detection • Spectroscopy of collision processes • Spectroscopy of Reactive collisions • Photon Assisted Collision Energy Transfer • Optical Cooling and Trapping • Single Ion Spectroscopy • Bose-Einstein Condensation • Optical Ramsey Fringes • Hi Gracie • Atom Interferometry • Spectral resolution within atomic line-widths • Absolute Optical Frequency Measurement and Standards • Optical Squeezing • Laser Induced Chemical Reactions • Laser Femtosecond Chemistry • Isotope Separation with lasers • LIDAR • Spectroscopy of Combustion Processes • Energy Transfer in DNA complexes • Laser Diagnosis and Therapy • AND SO ON…

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