Co laser: Advances in theory and experiment A. P. Napartovich, A. K. Kurnosov, S. L. Shnyrev, State Research Center Troitsk Institute for Innovation arid Fusion Research, 142190 Troitsk, TRINITI, Moscow region, Russia A. A.Ionin, Yu. M. Klimachev, A. A. Kotkov, L. V. Seleznev, D. V. Sinitsyn, Lebedev Physics Institute, 53, Leninsky prosp., 1 19991, Moscow, Russia ABSTRACT Last years, CO laser physics has been advanced by researches of CO overtone laser operated on high vibrational levels. An extension of kinetic model to multi-quantum vibration-vibration exchange and development of fully self-consistent model of CO laser are described. The theoretical model developed is verified by comparison with experimental data on overtone CO laser characteristics and laser gain dynamics. Current status of experimental achievements in CO laser characteristics in both fundamental and overtone bands are reported. Keywords: CO laser, fundamental band, overtone band, laser spectra, vibration-vibration exchange, gain coefficient 1. INTRODUCTION Development of CO lasers in kilowatt power range provides advantages over CO2 lasers in better focusability and transmission of the CO laser beam in optical fibers, reduced plasma shielding and different absorption depth in materials. At cryogenic temperatures, CO laser efficiency is about twice as large as that for CO2 laser. For some applications, of primary interest is the wavelength range, which covers spectral bands for many chemical compounds. The CO laser can be operated in two different spectral ranges: in the fundamental band (4.8÷8) tm (FB) and in overtone band (2.7÷4.2) tm. Because of comparatively more complicated physical processes in the CO lasers the approaches to design and development of devices with the power in kilowatt range are still not well established. The self-sustained dc and RE discharges and e-beam sustained discharge, as well, were implemented for pumping CO laser operated in the FB. There were known lab-scale CO lasers with subsonic and supersonic gas flows (see the overviews in [1, 2]). The CO overtone laser is still in a phase of research studies though a significant progress in its characteristics was demonstrated recently [3-5]. CO overtone laser operates between high vibrational-rotational levels on a long plateau in a distribution of molecules over vibrational levels. At high levels a vibration-vibration (V-V) exchange may proceed with a various number of quanta exchanged. It was shown that a realistic model should include multi-quantum exchange processes [3]. Probabilities for such processes are calculated theoretically. Recent progress in description of molecular collisions makes available computation of a full set of rate coefficients necessary to adequately model operation of CO overtone laser. This paper demonstrates how the most accurate modeling of V-V exchange processes in combination with self- consistent description of electron-molecule interactions agrees with experimental data on CO overtone laser characteristics. In particular, results on studies into laser gain dynamics for a number ofhigh overtone transitions will be reported. Comparison will be made with earlier existing numerical models of CO laser operated in fundamental and overtone bands. 2. EXPERIMENTAL REALIZATIONS OF CO LASERS 1. Fundamental band lasers The overview of earlier experimental realizations of CO lasers operating in the fundamental band is given in [1, 2]. Therefore, here an emphasis is made on achievements reported last years. The most flexible means to excite effectively CO laser mixture is an e-beam sustained discharge (EBSD). In particular, cryogenic cw CO laser excited by the EBSD was developed in [6], which operates in laser mixture CO:N2=l:9 with gas flow rate 1 kg/s of pre-cooled gas (temperature 90 K). Total power 85 kW was demonstrated at electro-optic efficiency (25-30)%. Output laser beam has sizes 10x5 cm2, operating time up to 5 s. Taking care about the deep gas cleanup, the e-beam current density on the Invited Paper XV International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers, edited by Jarmila Kodymová, Proc. SPIE Vol. 5777 (SPIE, Bellingham, WA, 2005) · 0277-786X/05/$15 · doi: 10.1117/12.611074 408 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 12/02/2013 Terms of Use: http://spiedl.org/terms