Long-path intracavity laser for the measurement of atmospheric trace gases

Abstract

Methods to increase the sensitivity of intracavity laser spectroscopy (ILS) have been investigated with application to the measurement of trace gases in the atmosphere. Recent theory has predicted that a longer laser cavity can give an increase in the limiting sensitivity of ILS. Measurements have been performed on a dye laser with two different cavity configurations, with lengths of 54 and 160 cm. No significant difference in the limiting generation time t(g) for these two laser lengths is found. The limiting t(g) of approximately 1000 microsec is achieved at pump powers of 150 to 300 mW, corresponding to 1.5 times the threshold power. When a tuning pellicle is introduced in the cavity, the laser linewidth is halved, the threshold power increases to 220-400 mW and the limiting t(g) decreases to approximately 400 microsec. Other effects at long generation times that will influence the use of ILS for atmospheric measures have been investigated. The spectral noise increases strongly near the limiting t(g), and the spectrum may show structure due to weak interferences in the laser cavity.