Computer Science
Scientific paper
Sep 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994spie.2266..500l&link_type=abstract
Proc. SPIE Vol. 2266, p. 500-509, Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research, Jinxu
Computer Science
1
Scientific paper
This work is based on the use of diode lasers as spectroscopic sources for the observation and study of weak overtone bands of the NIR. The diode laser emission wavelength can be scanned around a gas resonance by sweeping its injection current, permitting a direct observation of an absorption line-shape. The resolution is limited principally by the effective laser linewidth, generally approximately equals 20 MHz in free running mode. The signal-to-noise ratio is increased by using the frequency modulation technique, and the excess laser amplitude 1/f noise is reduced by working at high frequencies. Since detectors operating at high frequencies are expensive and less sensitive, a good compromise is the two-tone frequency modulation technique, which uses two close high frequencies and collects the beat signal at lower frequency. Pressure broadening coefficients have been measured for some acetylene and ammonia absorption lines in the 790 nm bands and new lines have been observed. Pressure shift of two acetylene lines have been examined. It is shown that this spectroscopic apparatus can extract very weak signals from the background and can be a good choice when the space occupied by the spectrometer needs to be restricted into small volumes.
Gabbanini Carlo
Gozzini S.
Longo Iginio
Lucchesini Alessandro
Pelliccia Daniele
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