Abstract

Use of lasers in spectroscopy has been demonstrated for several years by techniques as different as photoacoustic, optogalvanic, laser-induced fluorescence photoionization, and more recently frequency modulation. Each of these methods depends on some parameters which need calibration before quantitative measurements are made. Here we discuss a new type of high sensitivity intracavity laser absorption spectroscopy (ICLAS). Discovered fifteen years ago, this technique has now become more than just a curiosity. We show that if the laser is controlled in time (generation time) and the spectrum also resolved in time, ICLAS is similar to classical absorption with the advantage of an adjustable optical path length created by variation of the generation time.¹ Path length of more than 100 km can in principle be obtained. We discuss the discrepancy in sensitivity obtained by different authors and show that the sensitivity can be completely explained by a time-dependent theory published by Mironenko and Yudson.² Description of an intracavity laser spectrometer with a sensitivity of α = 10⁻⁹ cm⁻¹ and a resolution of λ/Δλ = 800.000 is presented. The limitation in sensitivity is discussed.

© 1985 Optical Society of America