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ULTRA-BROAD BANDWIDTH CAVITY ENHANCED ABSORPTION SPECTROSCOPY Paul S. Johnston Kevin K. Lehmann Department of Chemistry University of Virginia.

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Presentation on theme: "ULTRA-BROAD BANDWIDTH CAVITY ENHANCED ABSORPTION SPECTROSCOPY Paul S. Johnston Kevin K. Lehmann Department of Chemistry University of Virginia."— Presentation transcript:

1 ULTRA-BROAD BANDWIDTH CAVITY ENHANCED ABSORPTION SPECTROSCOPY Paul S. Johnston Kevin K. Lehmann Department of Chemistry University of Virginia

2 University of Virginia Department of Chemistry Cavity Enhanced Absorption Measure time integrated intensity R. Engeln, G. Berden, R. Peeters, G. Meijer, Rev. Sci. Instrum. 69 1998 3763. R>99.98% Time Intensity

3 University of Virginia Department of Chemistry Prism Cavity G. Engel et al., in Laser Spectroscopy XIV International Conference, Eds. R. Blatt et al. pgs. 314-315 (World Scientific, 1999). Output Input  b 6 m radius of curvature p-polarization θb-δθb-δ

4 University of Virginia Department of Chemistry Prism Advantage Wide spectral coverage - Simultaneous detection of multiple species Compact ring geometry (optical isolation) No dielectric coatings (harsh environments) Tunable finesse for near impedance matching

5 University of Virginia Department of Chemistry Broadband Setup λ=1064 nm Rep Rate: 30 KHz Pulse Width: 10 ns ~ 0.07 cm -1 / pixel 2048 pixels Photon Counting PC fiber mode matching mirrors 2400 g/mm: 500-790 nm 1200 g/mm: 500-1580 nm

6 University of Virginia Department of Chemistry Supercontinuum Generation Fiber – D = 1040 nm – Length = 14.5 m – Dispersion: air hole array Input – Average power: 1.0 W – Rep rate: 29.41 KHz – Pulse energy: 34 μJ – Peak power: 3400 W Output – Average output power: 0.270 W (at input polarizer) – Loss of ~50% power through polarizer http://www.crystal-fibre.com

7 University of Virginia Department of Chemistry Supercontinuum Generation

8 University of Virginia Department of Chemistry Photon Lifetime Detection Reverse Time-Correlated Single Photon Counting stop Time Amplitude Converter (TAC) start preamp ADC PMT Laser Controller

9 University of Virginia Department of Chemistry Experimental Results Exposure: 200 s Counts/sec: ~ 600 Time Resolution: 48 ns Raw DataFitted Data

10 University of Virginia Department of Chemistry Modeling Cavity Loss Model: rms error = 7.48 ppm

11 University of Virginia Department of Chemistry Prism Cell

12 University of Virginia Department of Chemistry Broadband Detection Atmospheric OxygenAcetylene 6v CH Overtone

13 University of Virginia Department of Chemistry New Vacuum Chamber

14 University of Virginia Department of Chemistry Multichannel Scaler No pile up error Detect multiple photons per decay Collect multiple decays High count rates – <100 MHz

15 University of Virginia Department of Chemistry Acetylene 6ν CH Overtone Pressure: 300 Torr

16 University of Virginia Department of Chemistry Current and Future Work Stability of Supercontinuum High Power Supercontinuum – Amplify ps mode-locked laser – Spectral Densities >mW/nm Broadband Detection – FTIR Future Studies – InGaAs Camera – Combustion Studies: New Direction – Molecular beam experiments

17 University of Virginia Department of Chemistry Acknowledgements HongBing Chen Ryan Coleman Haifeng Huang Robert Fehnel Pam Chu NIST

18 University of Virginia Department of Chemistry White light sources http://www.crystal-fibre.com


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