Absorption by CS2 molecules on “hot” band emission lines from a TEA CO2 laser

Abstract

We have measured absorption of emission from a TEA CO 2 laser, lasing on hot band lines, in pure CS 2 and a mixture of CS 2 with air, and we have determined the optimal lines for optical excitation. Numerical modeling has shown that as the peak intensity of the pump radiation is increased, we observe absorption saturation, the extent of which decreases as the pressure increases. The major factor responsible for absorption saturation is the "rotational bottleneck" effect. Depending on the peak intensity of the radiation, addition of a buffer gas can lead to an increase or decrease in the absorption.Key words: CS 2 absorption, TEA CO 2 laser, hot band line. Introduction.In recent years, considerable attention has been focused on development of sources of highpower coherent radiation in the terahertz (THz) range. Such sources are promising for remote detection of explosives hidden under clothing, nondestructive testing of the quality of parts and structures, all-weather navigation systems, systems for medical, biological, and scientific applications etc. (see, for example, [1-4] and references cited therein). However, to date the terahertz range of the spectrum, "at the junction" between laser physics and microwave electronics, is insufficiently "provisioned" with coherent radiation sources from the standpoint of practical demands on the required set of output parameters.Earlier [5,6], the possibility was considered for obtaining high-power terahertz radiation using a gaseous active medium containing CS 2 molecules. In this case, lasing of terahertz radiation is possible, for example, on the vibrational-rotational lines of the 00 0 1-12 0 0 band (117 µm or 2.56 THz). For optical pumping of the vibrational-rotational transitions in the CS 2 molecule in the 10 0 0-00 0 1 channel (11.4 µm), it has been suggested to use pulsed or cw CO 2 lasers which are tunable over a broad spectral range and capable of efficiently lasing on 01 1 1-11 1 0 hot band lines (11.3 µm) [7]. This method, in contrast to "submillimeter" lasers, where lasing occurs between rotational sublevels of the same vibrational state, makes possible a major increase in the power and energy of the terahertz radiation. For this purpose, we especially need to select the parameters optimal for optical pumping.This work was devoted to studying the feasibility of efficient pumping of CS 2 molecules by the emission of a pulsed TEA CO 2 laser, lasing on hot band lines, with the aim of designing a laser in the terahertz range.Block diagram of the experimental setup. Absorption by the CS 2 molecules was measured from the transmission of the pump radiation through a cuvet with the active medium. Fig. 1 shows the block diagram of the experimental setup. As the pump source, we used TEA CO 2 laser 1, tunable on the 01 1 1-11 1 0 hot band lines in the 11.00-11.35 µm range with output energy ~0.5-0.2 J respectively. The stability of the output energy was ~5% [8]. The cavity of the TEA laser was formed by a totally reflecting mirror built into the rear cover of the laser a...

Terahertz generation by means of optical lasers

“…To describe all the variety of THz generation methods one has to add also the available THz lasers (masers) -sources with the inversion of population at THz-shifted energy levels. Among the possible THz lasers there are CO 2 -pumped or Raman gas lasers [21,22], and several types of semiconductor lasers [23][24][25][26]. Gas lasers provide generation at a number of narrow lines.…”