Analysis of experimental data obtained in study of cryogenic CO laser with glow discharge and cryogenic slab CO laser with RF discharge showed that oxygen concentration in laser mixture is much less than in initial gas mixture. With low oxygen content, ozone plays role of supplier of electrons in cryogenic discharge. Since ionization potential of ozone is somewhat higher than that of oxygen, and ozone quickly condenses on cold walls of cryogenic discharge, conversion of O2 to O3 is accelerated. In addition, in plasma-chemical reactions, ozone regenerates carbon monoxide after dissociation. Acceleration of ozone generation in cryogenic barrier discharge was experimentally demonstrated.
Different frequency conversion processes in the mid-IR were experimentally studied with slab RF discharge CO and CO2 lasers and various nonlinear crystals ZnGeP2, GaSe, BaGa2GeSe6, AgGaSe2 and PbIn6Te10 : second and third harmonic generation of CO laser; sum and difference frequency generation of CO and CO2 lasers. Mid-IR emission on hundreds of narrow spectral lines from 1.7 μm to 19.3 μm was obtained
Super-broadband mid-IR laser systems are under development in the Gas Lasers Lab of the Lebedev Physical Institute. These systems consist of different sorts of molecular gas lasers and various nonlinear crystals converting multi-line emission of those lasers into broadband radiation on sum and difference frequencies. As frequency converters, both main mid-IR nonlinear crystals such as ZnGeP2, GaSe, AgGaSe2 and new ones such as BaGa2GeSe6, PbIn6Te10 are applied. As radiation sources, repetitively-pulsed Q-switched lasers pumped by both longitudinal DC discharge and transverse slab RF discharge emitting microsecond pulses, and also actively mode-locked e-beam sustained discharge lasers emitting nanosecond pulses are applied. It was experimentally demonstrated for the developed laser systems to emit broadband radiation on hundreds spectral lines covering mid-IR range from ~1.7 to ~17 micron due to sum and difference frequency generation including third harmonic generation.
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.
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.
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.
Compact slab repetitively-pulsed RF discharge overtone CO laser is developed. Results of parametric study of the laser
with cryogenically cooled electrode system operating in sealed-off mode are reported. The average output power of the
laser was up to 0.5 W with maximal efficiency of ~1.5 %. More than ~80 ro-vibrational overtone CO laser lines
(summarizing two spectral ranges 2.5-3.1 μm and 3.1-4.2 μm corresponding to two sets of laser resonator mirrors used in
the experiments) were observed. Start-up experiments on development the laser head of new design with enlarged active
medium length (40 cm) were carried out. Preliminarily the output power of the overtone CO laser with the new laser
head reached 0.75 W at the efficiency up to 1 %.
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.
Overtone lasing and fundamental band tuning was for the first time obtained in a slab carbon monoxide laser. The
compact slab CO laser with active volume 3×30×250 mm3 was excited by a repetitively pulsed capacitive RF discharge
(81.36 MHz) with pulse repetition rate 100-500 Hz. The laser electrodes were cooled down to 120 K. Gas mixture
CO:Air:He at gas pressures 15-22 Torr was used. An optical scheme "frequency selective master oscillator - laser
amplifier" was applied for getting fundamental band tuning. Single line lasing with average power up to several tens of
mW was observed on ~100 rotational-vibrational transitions of CO molecule within the spectral range ~5.0 - 6.5
micron. Multiline overtone lasing was observed on ~80 spectral lines within the spectral range ~2.5 -4.0 micron, with
maximum single line average output power 12 mW. Total output power of the slab overtone CO laser came up to 0.3 W,
with maximum laser efficiency 0.5%. Results of parametric studies of the overtone CO laser including complicated time
behavior for laser pulses on different overtone vibrational-rotational transitions are discussed.
Actively mode-locked electron-beam-sustained-discharge CO-laser producing a train of ~5-15 ns (FWHM) spikes
following with repetition rate 10 MHz for both single-line and multiline mode of operation in the mid-IR range of
~5 micron was experimentally studied. Total laser pulse duration was ~0.5 ms for both mode-locked and free running
laser. Specific output energy in multiline CO-laser mode of operation was up to 20 J l-1 Amagat-1 and the laser
efficiency up to 3.5%. The active mode-locking was achieved for single-line CO-laser mode of operation in spectral
range 5.2-5.3 micron. This sort of radiation can be used for pumping an optical parametric amplifier for optical
stochastic cooling in Relativistic Heavy Ion Collider, for laser ablation, and for studying vibrational and rotational
relaxation of CO and NO molecules.
Experimental and theoretical study of influence of nitrogen oxides NO and NO2 admixtures in oxygen containing gas
mixture excited by pulsed electron-beam sustained discharge on input energy and time behavior of singlet delta oxygen
(SDO) luminescence was carried out. Temperature dependence of the constant of SDO relaxation by unexcited
molecular oxygen was estimated.
Parametric study of a slab first-overtone carbon monoxide laser was performed. The compact slab first-overtone CO
laser with active volume 3x30x250 mm3 was excited by a repetitively pulsed capacitive RF discharge (81 MHz or
60 MHz) with pulse repetition rate 100-500 Hz. The laser electrodes were cooled down to 120 K. Gas mixtures
CO:O2:N2:He with different component contents at gas pressures 15-22 Torr were used. Two laser resonator mirrors
sets were used in the experiments on multiline lasing. More than 100 spectral lines within the spectral range ~2.5-4.0
μm with maximum single line average output power 12 mW were observed. Total output power of the slab firstovertone
CO laser came up to 0.3 W, with maximum laser efficiency 0.5%. Special details of long time output laser
power behavior are discussed.
Actively mode-locked electron-beam-sustained-discharge CO-laser producing ~10 ns (FWHM) pulses repetition rate
10 MHz for both single-line and multiline mode of operation was experimentally studied. The total laser pulse duration
was ~0.5 ms for both mode-locked and free running laser conditions. The specific output energy in multiline CO-laser
mode of operation was up to 20 J l-1 Amagat-1 and the laser efficiency up to 3.5%. The active mode-locking was
achieved for single-line CO-laser mode of operation in the spectral range 5.2-5.3 micron. The radiation can be used for
laser ablation, for pumping an optical parametric amplifier in optical stochastic cooling of relativistic heavy ions, and
for studying vibrational and rotational relaxation of NO molecules.
Influence of nitrogen oxides NO and NO2 on specific input energy (SIE) and time behavior of singlet delta oxygen
(SDO) luminescence excited by pulsed e-beam sustained discharge in oxygen was experimentally and theoretically
studied. NO and NO2 addition into oxygen results in small increase and decrease of SIE, respectively, the latter being
connected with large energy of electron affinity to NO2. The addition of 0.1-0.3% nitrogen oxides was experimentally
and theoretically demonstrated to result in notable enhancement of SDO lifetime, which is related to a decrease of
atomic oxygen concentration in afterglow. There was experimentally demonstrated that for getting high SDO
concentration at gas pressure 30-60 Torr for the time interval less than ~0.5 s one needs to add not less than 0.2%
nitrogen oxides into oxygen. Temperature dependence of relaxation constant for SDO quenching by unexcited oxygen
was estimated by using experimental data on time behavior of SDO luminescence.
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.
Temporal behavior of small signal gain in pulsed CO laser amplifier operating with oxygen rich gas mixtures CO:He:O2 and CO:N2:O2 was experimentally studied. The rich content of oxygen in helium mixture (CO:He:O2 =1:4:2) resulted in ~8-fold increase of the maximum gain on low vibrational transitions (10->9) and strong absorption on high ones (21->20). A high efficient pulsed CO laser operating with gas mixture in which oxygen substituted for nitrogen was launched.
Small signal gain temporal behavior in pulsed CO laser amplifier operating with oxygen rich gas mixtures CO:He:O2
and CO:N2:O2 was experimentally studied. The rich content of oxygen in helium mixture (CO:He:O2=1:4:2) resulted in
~8-fold increase of the maximum gain on low vibrational transitions (10-9) and strong absorption on high ones (21-20).
A high efficient pulsed CO laser operating with gas mixture in which oxygen substituted for nitrogen was launched.
Small-signal gain time behavior for cryogenic pulsed e-beam sustained discharge CO laser amplifier on high (V>15) fundamental band vibrational transitions was studied experimentally for different CO containing gas mixtures including ones typical for CO lasers and amplifiers (CO:He and CO:N2), and CO:O2 used for singlet delta oxygen production.
Time behavior of gas temperature in CO containing gas mixture excited in pulsed electron-beam sustained discharge (EBSD) was experimentally studied under different experimental conditions. To study time behavior of gas temperature, the fact that the gas temperature is equivalent to the rotational temperature of gas molecules was used. Rotational distribution of the excited states of CO molecule was reconstructed from measured small-signal gain dynamics on different ro-vibrational transitions. The time behavior of small-signal gain was obtained with probe low-pressure CW CO laser for ten ro-vibrational spectral lines. Gas mixtures CO:He=1 :4 and CO:N2=1:9 typical for a CO laser were used. It was demonstrated that gas temperature grew from 1 10 K (initial temperature) up ~15O K for the first hundred microsecond after EBSD beginning and was staying at this value for a long time (more than 1 ms) for both gas mixtures. EBSD pulse duration was -3Oµs. The method of reconstruction of gas temperature time history was also applied for oxygen gas mixture CO:O2=1:20 at gas pressure 0.04 atm, which was used for obtaining singlet delta oxygen in EBSD. The method can be used for diagnostic of non-equilibrium gas mixtures containing CO molecule.
Small-signal gain time behavior for a pulsed e-beam sustained discharge CO laser amplifier operating on fundamental band vibrational transitions V → V-1 from 6 → 5 (λ ~ 5.0 μm) up to 32 → 31 (λ~7.5 μm) was studied both experimentally and theoretically at various parameters of active medium. Special attention was paid to the small-signal gain time behavior on high vibrational transitions (V > 15). As was previously shown by us, multi-quantum theoretical model of vibrational exchange has to be applied for a correct description of a CO laser operating on vibrational transitions V → V-1 with V higher than 15 instead of a single-quantum one. To make easier theoretical interpretation of the experimental results, the binary nitrogen free gas mixture CO:He = 1:4 was used in our experiments. Total gas density and initial gas temperature was 0.12 Amagat and ~100 K, respectively. The complete kinetic model of a CO laser taking into account multi-qauntum vibrational exchange was employed for theoretical description of the small-signal gain time behavior. The theoretical results were compared with the experimental data.
The capabilities of different molecular gas lasers in infrared absorption diagnostics of multicomponent mixture are evaluated and compared. Extended sets of vibration-rotational emission lines are used for the following lasers: CO2, HF, DF, NH3, N2O and CO (including fundamental and first overtone transitions). Analytical frequencies are selected for all indicated lasers using spectroscopic databases in order to detect organic and inorganic pollutants using either low- or high-resolution spectra. Comparison of absorption in the atmosphere is made for frequencies of different lasers. Absorption spectra are simulated for 38 component gas mixture. Quantitative parameters characterizing the sensitivity and the selectivity of specific gas detection are calculated and compared: minimum detectable concentration, partial sensitivity, partial selectivity. It is found that NH3 and CO lasers presently have the best spectroscopic detection characteristics.
The quantitative analysis of sensitivity and selectivity characteristics for spectroscopic gas detection with different mid-infrared molecular lasers was carried out. In particular, the partial and cross sensitivity, the partial selectivity and total parameter of selectivity and sensitivity for gas detection in gas mixture of seven components with HF, DF and first-overtone (FO) carbon monoxide lasers were calculated. The analysis demonstrated that FO CO laser due to its spectral properties is very perspective source of light for laser spectroscopy of multicomponent gas mixtures. The FO CO laser spectral range (2.5-4.2 microns) overlaps the 'transparency window' of the atmosphere in the wavelength range (~3 - 4 microns) and covers that of HF and DF lasers, with its ro-vibrational line spacing being several times less than that of those lasers. The FO CO laser spectral lines coincide with a large number of absorption lines belonging to numerous organic and non-organic substances which can be found in plasma induced by laser ablation. The linear and nonlinear absorption of the FO CO laser by different gaseous substances was calculated and compared with the experimental data.
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