Absorption of CH3OH around waveguide CO2 laser lines

Abstract

In the present work we have performed a systematic investigation of the absorption of CH OH around each of the normal CO 2 laser lines. A waveguide configuration, offering extended tunability (240 or 300 MHz depending on the particular cavity lenght) has heen used for the laser. An optoacoustic cell, equipped with Stark plates, have been used for detecting the absorption. The suitability of waveguide CO laser as pump sources of FIR emissions was already recognized (1,2,3). In case of complex rotovibrational spectra, like for CH 3 OH, many different absorptions are accessible within the tuning range of the CO 2 laser line. Nevertheless new saturation techniques in the three level scheme (4) can be successfully applied to assign the different transitions. The aim of the present investigation is helping the generation of new optically pumped FIR laser lines and the understanding of already known and new discovered rotovibrational molecular transitions. In the following some particular case will be illustrated: 9-P(20). In Fig. la) the laser mode is shown. The optoacoustic recording (b) displays at least three different absorptions at −83,' + 1+9 and +121 MHz. Only the central one is accessible to conventional sources, by which no FIR emissions have been reported to date (5). The FIR line at 51.3 μm, previously reported by a TEA laser (6), is now pumped CW (Fig.le). The excellent CO 2 laser spectral purity allows the detection of the Transferred Lamb dip and the determination of the offset (sign and magnitude) of the pump transition.