Doppler-Limited Absorption and Fluorescence Spectroscopy with Lasers

Abstract

In Vol. 1, Chap. 5 we presented the different realizations of tunable lasers; we now discuss their applications in absorption and fluorescence spectroscopy. First we discuss those methods where the spectral resolution is limited by the Doppler width of the molecular absorption lines. This limit can in fact be reached if the laser linewidth is small compared with the Doppler width. In several examples, such as optical pumping or laser-induced fluorescence spectroscopy, multimode lasers may be employed, although in most cases single-mode lasers are superior. In general, however, these lasers may not necessarily be frequency stabilized as long as the frequency jitter is small compared with the absorption linewidth. We compare several detection techniques of molecular absorption spectroscopy with regard to their sensitivity and their feasibility in the different spectral regions. Some examples illustrate the methods to give the reader a feeling of what has been achieved. After the discussion of Doppler-limited spectroscopy, Chaps. 2–5 give an extensive treatment of various techniques which allow sub-Doppler spectroscopy.