Yu. M. Klimachev

Non-self-sustained electric discharge in oxygen gas mixtures: singlet delta oxygen production

The possibility of obtaining a high specific input energy in an electron-beam sustained discharge ignited in oxygen gas mixtures O2 :A r :C O (or H2) at the total gas pressures of 10–100 Torr was experimentally demonstrated. The specific input energy per molecular component exceeded ∼ 6k J l −1 atm −1 (150 kJ mol −1 ) as a small amount of carbon monoxide was added into a gas mixture of oxygen and argon. It was theoretically demonstrated that one might expect to obtain a singlet delta oxygen yield of 25% exceeding its threshold value needed for an oxygen–iodine laser operation at room temperature, when maintaining a non-self-sustained discharge in oxygen gas mixtures with molecular additives CO, H2 or D2. The efficiency of singlet delta oxygen production can be as high as 40%.

Cascaded carbon monoxide laser frequency conversion into the 4.3–4.9 μm range in a single ZnGeP 2 crystal

Collinear cascaded mid-IR frequency conversion in a single nonlinear optical crystal was accomplished. Concurrent collinear generation of the sum frequency of multiline fundamental band carbon monoxide laser radiation as a first frequency conversion cascade resulted in collinear difference frequency generation within the 4.3 to 4.9 μm spectral range when mixing this sum frequency radiation with the fundamental one as the second cascade in the same ZnGeP(2) nonlinear optical crystal.

Glow Discharge in Singlet Oxygen

Currently, there is no experimental data on the plasma balance in gas mixtures with a high content of singlet delta oxygen O2(1Δg). These data can be obtained by studying the parameters of an electric discharge in singlet oxygen produced by a chemical generator. The O2(1Δg) molecules significantly change the kinetics of electrons and negative ions in plasma. Hence, the discharge conditions at low and high. O2(1Δg) concentrations are very different. Here, the parameters of the positive column of a glow discharge in a gas flow from a chemical singlet-oxygen generator are studied. It is experimentally shown that, at an O2(1Δg) concentration of 50% and at pressures of 1.5 and 2 torr, the electric field required to sustain the discharge is considerably lower than in the case when all of the oxygen molecules are in the ground state. A theoretical model of the glow discharge is proposed whose predictions are in good agreement with the experimental data.

Influence of nitrogen oxides NO and NO2 on singlet delta oxygen production in pulsed discharge

The influence of nitrogen oxides NO and NO2 on the specific input energy (SIE) and the time behaviour of singlet delta oxygen (SDO) luminescence excited by a pulsed e-beam sustained discharge in oxygen were experimentally and theoretically studied. NO and NO2 addition into oxygen results in a small increase and decrease in the SIE, respectively, the latter being connected with a large energy of electron affinity to NO2. The addition of 0.1–0.3% nitrogen oxides was experimentally and theoretically demonstrated to result in a notable enhancement of the SDO lifetime, which is related to a decrease in the atomic oxygen concentration in afterglow. It was experimentally demonstrated that to get a high SDO concentration at the gas pressure 30–60 Torr for a time interval of less than ~0.5 s one needs to add not less than 0.2% nitrogen oxides into oxygen. The temperature dependence of the relaxation constant for SDO quenching by unexcited oxygen was estimated by using experimental data on the time behaviour of SDO luminescence.

Broadband two-stage frequency conversion of CO laser in AgGaSe(2) crystal.

For the first time, to the best of our knowledge, a broadband two-stage frequency conversion of multiline CO laser radiation was theoretically and experimentally demonstrated in a single AgGaSe2 crystal. The first stage is sum frequency generation of CO laser radiation. The second stage is concurrent difference frequency generation within 4.3-4.9 μm spectral range when mixing sum frequency radiation with the pump radiation in the same AgGaSe2 crystal. Internal sum frequency generation efficiency of multiline CO laser was up to 1%, while internal difference frequency generation efficiency was up to 0.065%.

Frequency tunable CO laser operating on the highest vibrational transition with wavelength of 8.7 .MU.m

A carbon monoxide laser emitting on the highest ever observed vibrational transition with a wavelength of 8.7 μm was for the first time launched. An influence of gas mixture content on the CO laser spectrum and factors limiting the longest CO laser wavelength are discussed.

Mid-IR Zeeman spectrum of nitric oxide molecules in a strong magnetic field

Nonlinear Zeeman splitting of ro-vibrational spectral lines of nitric oxide molecules in a variable magnetic field with maximum induction up to 6 T was studied both experimentally and theoretically. A single line frequency-tunable CO laser operating in the wavelength range of ~5–6 µm was employed to detect absorption of its radiation by NO molecules versus time, i.e. to detect laser magnetic resonance (LMR) spectrograms. These LMR spectrograms were simulated with a numerical model in which Zeeman shifting of ro-vibrational energetic levels in the magnetic field was calculated with the perturbation theory of different orders. The observed LMR spectrograms appeared to be in adequate agreement with the numerical data calculated in the third order of the perturbation theory.

Frequency doubling and mixing of the radiation of carbon monoxide lasers in nonlinear ZnGeP 2 and GaSe crystals

Frequency doubling of the radiation of selective and nonselective carbon monoxide lasers in nonlinear ZnGeP2and GaSe crystals has been experimentally investigated. An internal frequency-conversion efficiency as high as 7% has been obtained, with enrichment of the spectrum of the converted frequencies due to the parallel process of sum-frequency generation. The possibility is discussed of using the methods of nonlinear crystal optics to create a broad-range coherent-radiation source in the mid-IR and terahertz ranges of the spectrum, based on carbon monoxide lasers.

Theoretical modelling and experimental studies of the multi-quantum vibration exchange in vibrationally excited CO molecules

Studies of the vibration-vibration (VV) exchange in CO molecules excited up to vibration quantum numbers v = 20 have been performed both theoretically and experimentally. A new kinetic model which takes into account the multi-quantum VV exchange in the temperature range T = 100-300 K is described for the first time. A description is given of the experimental methodology allowing for studies of the effects of the relaxation of the vibrational distribution after a sudden disturbance. The disturbance of the vibrational distribution is produced by a Q-switched short pulse of single line radiation in fundamental band. The relaxation is studied by measuring the laser pulse energy of the second pulse initiated by resonator Q-switching produced with a variable time delay relative to the first pulse. A set of kinetic rate constants accepted in the model for various gas temperatures, vibration level numbers and number of exchanged vibration quanta from 1 to 4 is presented. The good agreement between the experimental data and the results of the advanced theory is the first direct evidence in support of the multi-quantum exchange model.

Frequency conversion of radiation of IR molecular gas lasers in nonlinear crystals (A review)

The solution of problems related, e.g., to transport of laser radiation in the atmosphere requires availability of a broadband IR laser source operating in the transparency windows of the atmosphere. In this review, we present the results of an investigation of the properties of a hybrid laser system consisting of molecular gas pump lasers and a solid-state laser frequency converter based on nonlinear crystals. We demonstrate broadening and enrichment of spectrum of radiation of the pump laser by means of sum- and difference-frequency generation. In particular, by using a relatively simple laser system consisting of gas-discharge CO and CO2 lasers, radiation tunable over a large number of spectral lines in a broad range of wavelength from 2.5 to 16.6 µm (more than two and a half octaves), which includes two transparency windows of the atmosphere, is obtained. Thus, the possibility of exploring the IR spectral range by means of hybrid laser systems based on frequency conversion of radiation of molecular gas lasers is demonstrated.