Optics: measuring and testing – For light transmission or absorption – Of fluent material
Patent
1995-06-07
1997-06-03
Hantis, K.
Optics: measuring and testing
For light transmission or absorption
Of fluent material
250343, 356409, G01N 2161
Patent
active
056360355
ABSTRACT:
A method and apparatus for conducting laser absorption spectroscopy uses a frequency tunable laser aligned to pass a laser beam through a sample volume and to an optical detector. A two-step modulation is used to generate frequency components that may be used to both lock the tunable laser to the absorbance signal, and generate an output signal proportional to the absorbance signal. The method includes frequency modulating the tunable laser at a first frequency while further modulating the tunable laser with a triangular waveform having a second frequency, and generating a feedback control signal based upon an antisymmetrical signal demodulated from the optical detector using a first predetermined harmonic of the second frequency. The tunable laser is locked to the absorbance signal with the feedback control signal. An output signal proportional to the absorbance signal is generated using a symmetrical signal demodulated using a second predetermined harmonic of the second or triangular waveform frequency. The first and second predetermined harmonics are preferably consecutive harmonics.
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Sun Hoi C.
Whittaker Edward A.
Hantis K.
The Trustees of the Stevens Institute of Technology
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