Ultrasensitive Analysis Of Trace Atmospheric Species Using Diode Lasers: A Comparison Of High Frequency Modulation Techniques.

Abstract

Numerous frequency modulation techniques are now available to overcome the large excess noise inherent to diode laser operation at low frequencies. In some cases, shot noise limited laser performance has been obtained with measured absorbances as low as 10-7. Combination of these novel methods with the long (10-100 m) optical paths provided by multipass cells makes feasible sub-part-per-billion detectivities for many gaseous compounds.