Тысячи-1 / Molecular Gas Laser Group

Molecular Gas Laser Group

EBSD molecular laser with active volume of 10 liters. Output energy: 800 J (fundamental band СО, ~5-6 μm); 500 J (СО₂, =10.6 μm); 100 J (N₂O, =10.9 μm);   50 J (overtone СО, ~3 μm ).

 

Nonequilibrium vibrational kinetics of CO laser active medium was experimentally studied together with TRINITI and the High Temperature Institute (Russia). The kinetic model taking into account multiquantum exchange processes was developed on the basis of modern point of view about physical processes going in multilevel active medium of a CO laser. The experimental procedure using a double Q-switching of a frequency selective CO laser was applied. The procedure enabled us to produce a short disturbance of a vibrational distribution function (VDF) on selected ro-vibrational transition and to measure the time behavior of the VDF relaxation. The calculations made for these experiments demonstrated that, when modeling an active medium of a CO laser including an overtone CO laser operating on highly excited (V>15) vibrational transitions, one have to apply the multiquantum exchange model.

The experimental and theoretical research of a pulsed EBSD first-overtone CO laser was done together with the Troitsk Institute of Innovation and Thermonuclear Research (TRINITI) (Russia), AFRL and the University of New Mexico. The research demonstrated the overtone CO laser to operate within the spectral range of 2.5 - 4.2 μm that entirely covers up the atmospheric transparency window ( ~3.3 - 4.1 μm). The laser can be considered as an electric analog of a chemical HF(DF) laser. The experimentally obtained laser efficiency comes up to 11%, theoretical one being up to 20%. The frequency selective overtone CO laser operates on more than 400 spectral lines. Small-signal gain on highly excited vibrational transitions is up to 0.4 m^-1. The experimental and theoretical results on the overtone CO laser has given us a real scientific basis for launching an RF discharge supersonic CO laser at the AFRL. Joint research of the supersonic CO laser made by our lab, AFRL (USA), University of New Mexico (USA) and DLR Technical Physics Institute (Germany) demonstrated its lasing on overtone transitions. Qualitative and quantitative analysis of spectral characteristics of the overtone CO laser and HF(DF)  lasers demonstrates that the overtone CO laser has the best parameters of sensitivity and selectivity, if one is going to use the overtone CO laser as a radiation source for the spectral analysis of multicomponent gas mixtures.

The procedure of study of nonlinear optical properties of a laser active medium was experimentally and theoretically developed. The procedure is based on detection and analysis of a phase- conjugation signal time behavior at intracavity degenerate four-wave mixing of laser radiation in the own active medium. Nonequilibrium kinetic processes taking place in the active medium manifest themselves in transient time behavior of the phase-conjugation signal. Experimental and theoretical study made together with the Institute of Applied Laser-Information Technologies (IALIT), "Astrophysics" Company(Russia) and the Directorate of Applied Technology (USA) demonstrated that the formation of a phase-conjugation signal in active medium of a pulsed EBSD CO₂ laser is related to two nonlinear mechanisms- resonant and thermal ones. The high energetic efficiency up to 20% for the intracavity phase conjugation in an active medium of the CO₂ laser is due to the properties of inertial thermal nonlinearity, energy loaded into an electric discharge and gas pressure being the most influential factors. The same method was for the first time applied together with TRINITI to the study of nonlinear properties of an active medium of a pulsed CO laser having quite different mechanism of inversion formation and, accordingly, quite a different influence of resonant and thermal mechanisms of nonlinearity. The results obtained can be used for developing high-power laser systems and improving their angular divergence. The procedure itself can be applied for the research of nonlinear optical properties of various laser media. For instances, the study of a turbulent diffusion in an active medium of a fast axial flow CO₂ laser was fulfilled at the IALIT together with the Gas Laser Lab participation.

 The procedure of multiline laser probing for studying active medium containing CO got its further development. Time behavior of local parameters of active medium (such as local specific input energy, gas temperature and population of CO vibrational levels) pumped by EBSD was obtained by using experimentally detected time behavior of small-signal gain / absorption coefficient with probing CO laser on 10 spectral lines. In particular, gas temperature and population time behavior was measured with high accuracy (~5%) for various gas mixtures СО:Не, СО:N₂ и CO:O₂

Pulsed CO and CO2 lasers developed at the lab were used in various experiments on laser-matter interaction. The experiments on laser-rock interaction were carried out together with the Colorado School of Mines, Solution Engineering (USA) and Moscow State Mining University for rocks typical for oil fields. Different types of sandstones, limestone, shale and granite saturated by water or mineral oil, or dry were irradiated by laser radiation. The energy density and intensity of laser radiation on a rock sample came up to 103 J/cm2 and ~ 107 W/cm2.

  For various rocks the dependencies of specific laser energy needed for excavation of volumetric unit of rock upon the energy density, the number of laser pulses, rock surface conditions, etc. were experimentally obtained. Measurements of a specific mechanical momentum by a ballistic pendulum, which enabled us to get a coupling coefficient, and application of high-speed photography, gave us an opportunity to estimate an ablation pressure in interaction area and a velocity of expanded plasma plume for different gas dynamic regimes. The analysis of absorption and reflection IR spectrum made for rocks before and after the laser treatment demonstrated a surface crystal structure modification. Three mechanisms of rock destruction were demonstrated to take place in the experiments with dry and wet rocks: a) dry rock ablation; b) water boiling in a surface layer of porous rock saturated by water and following explosive water vapor expansion leading to the efficient rock destruction; c) rock destruction by a shock wave arising in rock when screening laser plasma by a thin layer of liquid transparent for the IR radiation.

  The experiments on interaction of frequency selective pulsed EBSD CO laser radiation with polymer materials such as nylon and other one having  intense absorption bands  near the wavelength ~6 μm  were carried out together with DuPont (USA). The objective of the research was a formation of periodic structures on polymer fiber surface. The interaction parameters such as a geometry and a procedure of irradiation of polymer surface by laser radiation, energetic, spectral and temporal characteristics of laser radiation corresponding to different sorts of microstructures on fibers of treated polymer were determined.The connection between these microstructures and macrochanges of polymer surface such as a threshold of destruction, elimination of surface brilliance, etc. was analyzed. It was demonstrated that the procedure of using laser radiation for the treatment of polymer fabric consisted of fibers ~10-20 μm in diameter enabled us to form various periodic structures with a period of 3-5 μm. The procedure can be used for changing surface properties of polymer fabrics and production of optical fibers with surface periodic structures.

 

 Experimental and theoretical study of a possibility of molecular singlet delta oxygen O₂(а¹_g) (SDO) production in different sorts of electric discharge including EBSD with a yield adequate for developing electric discharge oxygen-iodine laser has been started at the Gas Laser Lab together with the Chemical Laser Lab and TRINITI. Study of electric breakdown and volt-ampere characteristics of a glow discharge in SDO was completed. SDO and the ground state oxygen turned out to have quite different electric properties . A drop of breakdown voltage in electric discharge ignited in SDO was experimentally observed, which is related to lower SDO ionization potential as compared to the ground state oxygen. Good agreement between experimental and theoretical results gives an opportunity of calculation of SDO ionization cross-section by shifting the ground-state oxygen ionization cross-section by Е=0.98 eV down to energy axis.

Electric properties and spectroscopy of EBSD in oxygen and oxygen gas mixtures at gas pressure up to 200 Torr were experimentally and theoretically studied together with Chemical Lasers Lab and TRINITI. The pulsed discharge in pure oxygen and its mixtures with noble gases was shown to be very unstable and characterized by low input energy. When adding small amount of carbon monoxide or hydrogen, the electric stability of the discharge increases, specific input energy (SIE) per molecular component being more than order of magnitude higher and coming up to 6.5 kJ/(l atm) for gas mixture O₂:Ar:CO = 1:1:0.1. Experiments on spectroscopy of the SDO and O₂(^_g⁺) states in the EBSD were carried out. The calibration of the optical scheme for measuring the SDO absolute concentration and yield using the detection of luminescence of the SDO going from a chemical SDO generator was done. Temporal behavior of SDO concentration and yield in the EBSD afterglow was analyzed. Experimentally measured SDO yield for oxygen mixture O₂:Ar:CO=1:1:0.05 at total gas pressure 30 Torr comes up to 10.5% at SIE of ~3.0 kJ/(l atm(O₂+CO)), whereas its theoretical value riches ~17%. A part of the energy loaded into the EBSD goes into the vibrational energy of the molecular admixture, which was experimentally demonstrated by launching a CO laser operating on an oxygen-rich mixture O₂:Ar:CO = 1:1:0.1 and measuring its small-signal gain.

Singlet delta oxygen O₂(а¹_g) production in slab discharges ignited in oxygen gas mixtures was experimentally studied together with Chemical Lasers Lab and Department of Optics. In slab self-sustained RF discharge experimental SDO yield was about 10%. It was demonstrated that the choice of electrodes’ material is very important. Experiments on SDO production in slab non-self-sustained discharge with external ionization by repeated high-voltage pulses were carried out. SDO concentration was measured by the method of intracavity laser spectroscopy. The measured concentration of SDO was about 10¹⁶ cm^-3, with SDO yield being of ~7%.

Pulsed ammonia NH₃ laser optically pumped by CO₂ laser radiation was developed at the lab. The laser operates within ~11-14 μm spectral range, to which absorption spectra of many harmful freons belong. The design of a double frequency lidar using frequency selected CO₂ laser radiation as a reference beam and  a frequency  tuned NH₃ laser radiation as a measuring beam was developed. It was demonstrated that such a lidar operating within 9-14 μm spectral range can be used for remote sensing of freons and other atmospheric pollutants with concentration of ~1 ppt. The lidar can be used as a mobile one located in a mini-van. The weigth and size of such a device are 300 kg and 2.5x1.7x1.3 m³.