A. A. Kotkov

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%.

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 30–60u2009Torr for a time interval of less than ~0.5u2009s 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.

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.

Broadband hybrid IR laser system emitting within 2.5-16.57 micron

Laser system emitting within IR wavelength range from 2.5 to 16.57 micron is discussed. The hybrid laser system consists of molecular gas lasers with a frequency conversion in a nonlinear crystal. One gas laser is a carbon monoxide laser operating in multi-line or single-line mode. Another one is a carbon dioxide laser operating in multi-line mode. These lasers operate in a Q-switched mode. The laser emission is mixed in various nonlinear crystals producing sum and difference frequency conversion into above mentioned broadband IR spectral range.

CO laser frequency conversion in nonlinear crystals ZnGeP2 and GaSe

Experimental and modeling results on CO laser frequency conversion are presented. A Q-switched multiline CO laser with pulse repetition rate 20-150 Hz of sub-microsecond pulses and electron beam sustained discharge frequency-tunable mode-locked CO laser were used in the experiments on second harmonic generation (SHG) in high-quality ZnGeP2 and GaSe crystals. Internal SHG efficiency exceeded 12.4 % in 12 mm ZnGeP2 crystal. The SHG in 4 mm GaSe crystal was observed with internal efficiency of 0.3%. A possibility of difference frequency generation of fundamental and firstovertone CO laser lines to cover spectral range of ~4.0-5.0 μm is discussed. It is estimated that the difference frequency generation of neighboring lines of both fundamental and first-overtone bands allows one to obtain oscillation in THz spectral range within ~200-3000 μm.

Nonlinear zeeman splitting of nitric oxide spectral lines in magnetic field

The Zeeman splitting of NO molecule ro-vibrational spectral lines in strong magnetic field was calculated and compared with experimental data. The nonlinear Zeeman splitting takes place in magnetic field of ~1 T and stronger.

Zeeman Effect treatment in the infrared spectrum of the nitric oxide molecule

The results of experimental and theoretical study of the Zeeman splitting of the vibrational-rotational lines in the NO molecule as a function of magnetic field are presented. To record the spectrum the method of laser magnetic resonance (LMR) with using continuous wave frequency-tunable CO laser has been applied. To analyze experimental data of Zeeman splitting, the calculation procedure was developed. This procedure is based on the numerical diagonalization the matrix of the effective molecular Hamiltonian, which includes Zeeman operator corresponding to interaction an external magnetic field with a molecule.

Influence of multi-line CO laser focusing on broadband sum-frequency generation

An influence of multi-line CO laser focusing on spectral characteristics of broadband sum-frequency generation in ZnGeP2 nonlinear crystal was experimentally and numerically studied. Maximal frequency conversion was experimentally observed under tight focusing of the multi-line rather than single-line CO laser. The tight focusing resulted in broadening sum-frequency generation spectrum and increasing total, i.e. integrated over the spectrum, frequency conversion efficiency. These effects were due to increasing phase-matching bandwidth and angular dispersion. Maximal conversion efficiency of the multi-line CO laser was numerically demonstrated to take place at the focal length of 0.4 times that for the single-line one.

MOPA carbon monoxide laser system emitting nanosecond pulses

A Master Oscillator - Power Amplifier (MOPA) carbon monoxide laser system emitting nanosecond pulses was developed on the basis of the wide-aperture pulsed electron-beam-sustained-discharge CO-laser facility. Amplification parameters including gain and saturation intensity of amplifying media consisted of gas mixtures CO : He or CO : Ar were measured. The MOPA system emitted a train of nanosecond pulses with peak power up to ~0.1MW on a single spectral line and up to ~0.4MW with multiline spectrum.

Spectroscopic analysis of multicomponent gas mixtures with wide range carbon monoxide laser

Possibility to apply wide range CO-laser for detection of trace gas pollutions in multicomponent gas mixture is studied both theoretically and experimentally. Parameters of sensitivity and selectivity for multicomponent gas analysis with CO-laser were calculated.