Optics: measuring and testing – For light transmission or absorption – Of fluent material
Patent
1991-09-30
1993-11-30
McGraw, Vincent P.
Optics: measuring and testing
For light transmission or absorption
Of fluent material
250343, 356409, G01N 2135, G01N 2161
Patent
active
052670198
ABSTRACT:
A method and apparatus using a frequency tunable laser to generate a beam which passes through a sample cell and onto an optical detector wherein the tunable laser is modulated at a predetermined frequency which has the undesired effect of producing a periodic interference fringe near an absorption induced signal. An additional level of modulation is applied to the laser beam by a triangular waveform having a predetermined peak-to-peak amplitude and frequency. The triangular waveform peak-to-peak amplitude produces a frequency swing of the laser beam so as to generate from the periodic interference fringe, a signal having reduced components near the absorption induced signal. The signal at the optical detector is demodulated by a lock-in amplifier tuned to a predetermined harmonic of the frequency of the triangular waveform.
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Sun Hoi C.
Whittaker Edward A.
Consortium for Surface Processing, Inc.
Hantis K. P.
McGraw Vincent P.
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