Electronic resonance enhanced coherent anti-Stokes Raman scattering technique for detection of combustion species and biological molecules

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Title: Electronic resonance enhanced coherent anti-Stokes Raman scattering technique for detection of combustion species and biological molecules
Author: Hanna, Sherif Fayez
Abstract: The application of electronic -resonance enhanced (ERE ) coherent anti -Stokes Raman scattering (CARS ) for the detection of nitric oxide (NO ) and acetylene (C2H2 ) is experimentally demonstrated and the effects of various parameters on the ERE CARS signal investigated . In addition , the detection of dipicolinic acid (DPA ) using ? ? ? ? ? ?normal ? ? ? ? ? ? CARS is demonstrated . For NO detection , the frequency difference between a visible Raman pump beam and Stokes beam is tuned to a vibrational Q -branch Raman resonance of the No molecule to create a Raman polarization in the medium . The second pump beam is tuned into resonance with the rotational transitions in the (1 ,0 ) band of the A2 ? ? ? ?+ -X2 ? ? ? ? electronic transition at 236 nm , and the CARS signal is thus resonant with transitions in the (0 ,0 ) band . A NO gas cell was used for the experiment to detect NO at various pressure levels . A significant resonant enhancement of the NO CARS signal was observed and good agreement between calculated and experimental data was obtained . For C2H2 detection , ERE CARS experiments were performed in a roomtemperature gas cell using mixtures of 5000 ppm C2H2 in N2 . Visible pump and Stokes beams were used , with the frequency difference between the pump and Stokes tuned to the 1974 cm -1 ? ? ? ?2 Raman transition of C2H2 . An ultraviolet probe beam with the wavelengths ranging from 232 nm to 242 nm is scattered from the induced Raman polarization to generate the ERE CARS signal . The effects of probe wavelength and pressure on signal generation are discussed . CARS was used to detect the 998 cm -1 vibrational Raman transition from a sample of polycrystalline DPA . The transition is the breathing ring vibration in the pyridine ring structure in the DPA molecule . The DPA 998 cm -1 transition is detected with excellent signal -to -noise ratio and the full -width -at -half -maximum is very narrow , approximately 4 cm -1 .
URI: http : / /hdl .handle .net /1969 .1 /4379
Date: 2006-10-30

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Electronic resonance enhanced coherent anti-Stokes Raman scattering technique for detection of combustion species and biological molecules. Available electronically from http : / /hdl .handle .net /1969 .1 /4379 .

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