Dual-modulation laser line-locking technique for wavelength modulation spectroscopy
U. S. Patent 6,351,309, issued February 26, 2002
Wavelength modulation spectroscopy using tunable diode lasers is a fast
and accurate way to measure trace gas concentrations. The fastest time response
is obtained by locking the laser to the peak of the absorption feature being
monitored. Sometimes sensitivity is limited by slow variations in the baseline
which make it difficult to detect sharp, narrow spectral features. 
The invention by David Bomse, Chris Hovde and Joel Silver of Southwest Sciences
uses two modulations of the laser wavelength, one at high frequency (say 1
MHz, a million modulation cycles per second) and one at lower frequency (say
10 kHz or 10,000 cycles per second). By using two modulations and two demodulation,
spurious background signals are reduced. Additional details can be found in
"A Dual Modulation Laser Line Locking Scheme," D. S. Bomse, Appl.
Opt.
Contact Information
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