Compact HF-pumped slab CO laser

Compact HF-pumped slab CO laser

In recent times, significant progress has been achieved in the development of capillary and slab gas lasers (including flow and sealed-off CO₂ and CO lasers) with diffusion cooling, excited by a capacitive transverse high-frequency (HF) discharge. In these lasers, heat from the gas mixture is extracted via cooled electrodes, to which an exciting HF voltage is applied. The HF discharge has a number of advantages as compared with the simplest and frequently used direct current discharge. The CO laser is known to demonstrate the best output characteristics at cryogenic temperatures of the active gas mixture. This is especially topical for an overtone CO laser [A.A. Ionin et al. Laser Physics 21: 500 (2011)]. A task of practical importance is to develop a compact slab CO laser with HF excitation and diffusion cooling of its active medium to low temperatures. Such a laser, combining a relative simplicity and compact size peculiar of slab HF designs, and a high efficiency with a broad spectrum of generation characteristic of electric discharge CO lasers, can become a unique spectroscopic tool for detecting various explosive, toxic etc. hazardous substances and materials. The LGL created compact slab CO lasers with pumping by the capacitive HF discharge and cryogenic cooling of electrodes with various lengths of the active medium (250 and 400 mm).  The optimal conditions (composition and pressure of the gas mixture, parameters of the HF discharge) for the implementation of the best output laser characteristics were determined. The maximal experimentally obtained average power of a laser on the basic transitions of the CO molecule (spectral range, 5.1–5.4 μm) was ~12 W, and its efficiency factor reached ~14%. Also implemented was the frequency selective regime of operation of this laser. Single-frequency lasing was produced on ~100 laser lines within the spectral range of 4.9–6.5 μm with an average output power from several milliwatts to several tens of milliwatts. For the first time in a slab cryogenic CO laser with HF pumping, the generation of radiation was implemented on overtone transitions of the CO molecule in the spectral range of 2.5–4.0 μm. As the result of optimization of experimental parameters in the regime of free multi-frequency generation, an average power of ~2.0 W with an efficiency up to 1.6% was recently achieved. All results were obtained without a forced replacement of the gas mixture. Under fixed experimental conditions, the lasing was stable (with fluctuations of the output characteristics not more than 10%) for over one hour, which enables the statement that the sealed-off regime of operation of a cryogenic CO laser was first implemented.  The frequency tuning range of the CO laser overlaps the spectral ranges which include the absorption lines and bands of both common substances (H₂O, CO₂, O₃, N₂O, NO₂, NO, SO₂, NH₃ etc.) and organic compounds (such as methane, acetone, benzene, methanol, ethanol etc.) and strong pollutants. Owing to a large number of spectral lines, the CO laser is an attractive source of radiation for solving spectral analysis issues of both multicomponent gas mixtures and individual substances occurring in the atmosphere. Using an overtone CO laser, model experiments were conducted to measure concentrations of gases in a two-component mixture (N2O + CH4) in the region where their absorption spectra overlap. The accuracy of reconstructing the concentrations of gases in a multicomponent mixture was shown to increase with the number of laser lines increasing.

1. A.A. Ionin, A.Yu. Kozlov, L.I. Seleznev, D.V. Sinitsyn, RF discharge slab CO laser operating in both fundamental and first-overtone bands. Opt. Commun., 282, 629 (2009).
2. A.A. Ionin, A.Yu. Kozlov, L.V. Seleznev, D.V. Sinitsyn, Slab overtone CO laser operating in the 2.5-4.0 micron spectral range. IEEE J. Quantum Electron., 45(3), 215 (2009).
3. A.A. Ionin, A.Yu. Kozlov, L.V. Seleznev, D.V. Sinitsyn, A cryogenic slab CO laser. Quantum Electron., 39(3), 229 (2009).
4. A.A. Ionin, Yu.M. Klimachev, A.Yu. Kozlov, A.A. Kotkov, L.V. Seleznev, D.V. Sinitsyn,  An active medium for an electric-discharge CO laser or amplifier and a method of its pumping. Russian Patent 2354019 of 27/04/2009, Bulletin “Izobreteniya. Poleznye Modeli” (“Inventions. Useful Models”), No 12, p. 1016 (2009).
5. A. Ionin, A. Kozlov, L. Seleznev, D. Sinitsyn, Slab RF discharge overtone CO laser. Proc. SPIE, 7994, 79941N (2011).