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

摘要

Abstract: We have investigated methods to increase the sensitivity of intracavity laser spectroscopy, (ILS) 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. We have performed measurements on a dye laser with two different cavity configurations, with lengths of 54 and 160 cm. We find no significant difference in the limiting generation time (t$-g$/) for these two laser lengths. The limiting t$-g$/ of approximately 1000 $mu@s is achieved at pump powers of 150 to 300 mW, corresponding to 1.5 times the threshold power. When a tuning pellicle is introduced in the cavity, the laser linewidth is halved, the threshold power increases to 220-400 mW and the limiting t$-g$/ decreases to approximately 400 $mu@s. We have investigated other effects at long generation times that will influence the use of ILS for atmospheric measurements. The spectral noise increases strongly near the limiting t$-g$/, and the spectrum may show structure due to weak interferences in the laser cavity.!