Applications of coherent anti-stokes Raman spectroscopy (CARS)

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1978

OSTI ID:6264728

Laufer, G

New Coherent Anti-Stokes Raman Spectroscopy (CARS) techniques and their application to gas diagnostics and surface spectroscopy are presented. Hollow waveguides are shown to enhance CARS by two orders of magnitude for low pressure gases. Theoretical and experimental comparisons of signals generated by tight focusing in a cell with those generated in a hollow waveguide are presented. These arguments show that for low pressures, enhancements are on the order of the square of the waveguide length to the confocal beam parameter ratio. Maximum conversion, for oxygen, in the hollow waveguide occurs at pressures on the order of several atmospheres compared to greater than 50 atmospheres for tight focusing. A new crossed beam CARS configuration which produces an angularly separated CARS spectrum, eliminating the need for a spectrometer is studied. Since one of the driving laser beams is always linearly opposed to the dye laser, it may also be used as a dye pump and the experiment performed within the dye cavity for efficient laser energy utilization. With this arrangement, a broad bandwidth dye laser produces a several wave-number resolution spectrum from a small volume with relatively simple alignment. The spectrum of pyridine is scanned by varying the incidence angle of a probe beam. A simultaneous, spatially-separated spectrum from different constitutents within a gas can be obtained by using a fan shaped probe beam. In particular, separated CARS beams from nitrogen and carbon monoxide are simultaneously observed from a single sample volume. CARS techniques are used to obtain the Raman spectra of molecular species adsorbed to electrode surfaces. No such spectrum is observed. From ordinary Raman spectrum it is seen that surface damage is induced by the high intensity lasers and thus prevents CARS from being observed with nanosecond lasers.

• OSTI ID: 6264728
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400104* -- Spectral Procedures-- (-1987)
500200 -- Environment
Atmospheric-- Chemicals Monitoring & Transport-- (-1989)
54 ENVIRONMENTAL SCIENCES
AZINES
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL ANALYSIS
COHERENT SCATTERING
DYE LASERS
ELEMENTS
HETEROCYCLIC COMPOUNDS
LASER SPECTROSCOPY
LASERS
LIQUID LASERS
NITROGEN
NONMETALS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PYRIDINES
RAMAN SPECTRA
SCATTERING
SPECTRA
SPECTROSCOPY