Method and apparatus for enhancing laser absorption sensitivity

Details Method and apparatus for enhancing laser absorption sensitivity Method and apparatus for enhancing laser absorption sensitivity

1985-07-31

1987-08-04

Evans, F. L.

Optics: measuring and testing

By shade or color

Fluid color transmission examination

250339, 250343, 250373, 356 51, 356256, G01N 2117

Patent

active

046842586

ABSTRACT:
A simple optomechanical method and apparatus is described for substantially reducing the amplitude of unwanted multiple-interference fringes which often limit the sensitivities of tunable laser absorption spectrometers. An exterior cavity is defined by partially-transmissible surfaces such as a laser exit plate, a detector input, etc. That cavity is spoiled by placing an oscillating plate in the laser beam. For tunable diode laser spectroscopy in the mid-infrared region, a Brewster-plate spoiler allows the harmonic detection of absorptances of <10.sup.-5 in a single laser scan. Improved operation is achieved without subtraction techniques, without complex laser frequency modulation and without distortion of the molecular lineshape signal. The technique is applicable to tunable lasers operating from UV to IR wavelengths and in spectrometers which employ either short or long pathlengths, including the use of retroreflectors or multipass cells.

REFERENCES:
patent: 3435371 (1969-03-01), White
patent: 3731224 (1973-05-01), Dienes et al.
patent: 3868592 (1975-02-01), Yarborough et al.
patent: 4233569 (1980-11-01), Liu
patent: 4268800 (1981-05-01), Johnston, Jr. et al.
patent: 4438517 (1984-03-01), Bobb et al.
Reid et al., Applied Optics, vol. 19, No. 19, Oct. 1, 1980, pp. 3349-3354.

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