Propagation of radiation of the photo-initiated chain HF-chemical laser (in a wavelengths range 2.6 - 3.4 μ) through a
real atmosphere is studied experimentally. The coefficients of absorption by molecules CO2 and CH4 are measured for
spectral lines of the photo-initiated chain and discharge-initiated non-chain DF- lasers (3.6 - 5 μ). Experimental and
numerical dependences of a passing through an atmosphere of radiation integrated on spectrum of the HF- and DF-laser
are determined on a trace length up to (240-500) m and 16 km, respectively.
A creation of a laser with a wavelength in UV spectrum field, as an element of lidar systems, can be perspective for
monitoring of the atmospheric impurities. A gas laser on electronic transition D'→A' (342 nm) with optical pumping (I2-
laser) is based on collisional transfer of electronic energy between terms 3Σu
+(D) and 3Π2g(D') of iodine molecules. The
dependence of intensity of luminescence D'→A' on pressure of buffer gas for 25 substances was studied. Effective
working mixtures of I2-laser with optical pumping on a basis of perfluoroalkanes were found.
Results of the experimental and numerical study of system "master oscillator-power amplifier" (MOPA) of the pulsed chemical photo-initiated HF-laser on chain reaction in a mode of selection of the separate spectral lines and groups of lines are presented. The MOPA radiation energy for the separate spectral lines and their groups at operation of the MO in a mode of selection achieved 350 and 500 J, respectively, that in 2 - 4 times exceeds the radiation energy for these lines at operation of MO in a free running mode.
Numerical and experimental study of processes of absorption of pumping radiation of HF-laser, a laser oscillation and a radiation amplification in a (CO2+N2O) active medium of high pressure is carried out. Measurements and numerical estimation of an absorption coefficient for 21 spectral lines of the HF-laser radiation, which are strongly absorbed by the CO2 and N2O molecules, are performed. Measurements of an integral absorption coefficient for total pumping spectrum for the laser media of various content are carried out. About 63 and 35 % of radiation of the non-chain and chain chemical HF-laser, respectively, are absorbed using a four-component laser mixture. For the mono-component active media the maximum specific energy of an output radiation in 10 microns region, efficiency of an energy conversion and a small signal gain (12CO2 - 200 J/l, 18 %, 9 m-1 ; 14N2O - 100 J/l, 7 %, 6 m-1) are obtained. For two-component (12CO2+14N2O)-active media these parameters are 120 J/l, 7%, 7 m-1 at maximum laser energy 12 J.
According to the numerical estimation, a coefficient of conversion of energy accumulated in lasing mode to energy of a pico-second pulse in 10.6 micron region for mixture of the CO2 and N2O molecules may achieve 30 %.
M. Azarov, B. Alexandrov, V. Kuprenyuk, Yu. P. Maximov, V. Mashendzhinov, A. Yu. Rodionov, M. Rotinian, V. Sudarikov, N. Tret'jakov, I. Feodorov, A. Etzina
The numerical end experimental study of the energy and temporal characteristics of the output radiation of the CW medium-scale chemical HF/DF-laser with mechanical modulation of the optical resonator quality by the mirror rotation with frequency up to 1 kHz is carried out. In experiment, a peak power of the laser radiation pulses has exceeded the radiation power in CW mode of the HF-laser operation not less than in four times. The average power in repetitively pulsed mode is lower than one in CW mode, but it grows with increase of the modulation frequency. Time of the complete recovery of a small signal gain of the active medium, which is about 6 - 7 &mgr;s, is determined. Two numerical models are developed, which describe the dynamics of the laser oscillation in a mode of the resonator quality modulation for both HF- and DF-laser, some features of their operation are analyzed using these models.
The experimental study of a repetitively pulsed chemical HF laser operating on a chain reaction F2 +H2, initiated by the barrier electrical discharge with the inter-electrode gap 10 cm, with length of active medium 40 cm along optical axis has been carried out. The barrier electrical discharge with duration about 120 ns has shown a high stability, reliability and homogeneity at specific energy deposits up to 60 J / 1.
At the repetition pulses rate 10 Hz with the depleted fluorine-hydrogen mixture (20 % F2, 5 % H2), the mean laser power 500 W (a specific energy for one laser pulse E/V ≈ 11.6 J / 1, technical efficiency of 15.6 %) is achieved.
In the single pulse mode of the laser operation with the mixture 30 % F2, 12 % H2 the maximum pulse energy Emax = 100 J, the specific radiation energy E/V = 24 J / 1, the technical efficiency &hookn;tech = 28.4 % are obtained.
We have carried out both numerical and experimental studies of amplification of a short pulse of HF non-chain laser by a chain reaction amplifier. A small aperture laser was used as the master oscillator and a large aperture (100 cm2) one was used as an amplifier. Both lasers were discharge initiated. Output pulse shape and energy have been studied as a function of discharge triggering delay and gas mixture composition. Obtained results show that, in spite of the known differences of both spectral and temporal characteristics of non-chain and chain lasers, it is possible to create a high power HF MOPA system with pulse duration less than 100 ns, technical efficiency above 10% and energy close to the one of the amplifier in free lasing mode.
A few years ago, it has been demonstrated that the use of hydrocarbons such as C2H4 or C6H12 as hydrogen donor allows realizing high-volume discharges in SF6 based non-chain HF/DF gas mixture. Although high energy, short pulses and high repetition rates have been obtained, for some uses the specific output energy, the efficiency and, to a less extent, the optical quality of all these lasers remain insufficient. IT appears now that the only way to increase these values is to use chain reaction. But chain reaction is known to be delicate to control, especially when working at high repetition rate. This paper will describe recent work directed towards a better understanding of the discharge mechanisms and an increase of the efficiency and of the specific output energy of HF/DF pulsed lasers using chain reaction in discharge initiated repetitive and non-repetitive experiments. High volume discharge cells compatible with repetition rate have been realized. Discharge initiated repetitive chain reaction ash been studied up to 10Hz with large gap. Efficiencies as high as 70% have been obtained in single pulse experiments. Computer modeling allows now predicting satisfactorily the performances of discharge-initiated chain reaction HF/DF lasers as a function of electric circuit characteristics and gas composition.
Theoretical and experimental study of transverse optical pumping of the high-pressure multi-component (CO2+N2O)-laser medium is carried out. Possibility of high efficiency (15 - 20%) of conversion of the discharge pulsed HF-laser radiation (λ = 2.7 - 3 µm) with the pulse duration <1 µs to the stimulated emission (10 - 11 µm) of the broadband laser medium is shown.
The efficient repetitively pulsed (10 Hz) HF chemical laser initiated by barrier electric discharge with electrode gap 10 cm was realised. In mono-pulse mode specific output energy 3 and 23 J/l, technical efficiency (η) 3.4 and 26%, for non-chain and chain process, correspondingly, were obtained. In the repetitively pulsed (RP) mode of the laser operation at 10 Hz on the depleted fluorine-hydrogen mixture (20% F2, 5% H2) the mean laser power of 43 W was obtained (specific output energy E/V ~ 10 J/l, η=11.3%). The computational prediction for laser operation in repetitively pulsed mode at active length of about 0.5 m has shown the possibility of achievement of the specific laser energy about 15 J/l and technical efficiency up to 20%. Output laser specific energy ~ 14 J/l under RPCL conditions at length of active medium 0.37 m in mono-pulse mode was obtained in a good agreement with numerical prediction.
A few years ago, it has been demonstrated that the use of hydrocarbons such as C2H4 or C6H12 as hydrogen donor allows realizing high-volume discharges in SF6 based non-chain HF/DF gas mixture. However, for some uses, the specific output energy, the efficiency and, to a less extent, the optical quality of all these lasers remain insufficient. It appears now that the only way to increase these values is to use chain reaction. But chain reaction is known to be delicate to control, especially when working at high repetition rate. This paper will describe recent work directed towards a better understanding of the discharge mechanisms and an increase of the efficiency and of the specific output energy of HF/DF pulsed lasers by using chain reaction in discharge initiated repetitive and non-repetitive experiments. High volume discharge cells compatible with repetition rate have been realized. Discharge initiated repetitive chain reaction has been studied up to 10Hz with large gap. Efficiencies as high as 70% have been obtained in single pulse experiments. Computer modeling allows now predicting satisfactorily the performances of discharge-initiated chain reaction HF/DF lasers as a function of electric circuit characteristics and gas composition.
The theoretical and experimental study of the spectral and energy characteristics of radiation of the pulsed photoinitiated HF/DF-laser operating on the chain chemical process in the gas mixture F2(H2+D2):O2:He=3:1:0.3:6.7 of atmospheric pressure depending on the relation between the initial concentrations H2 and D2 and the oscillation threshold is carried out. The optimum requirements for a simultaneous oscillation on molecules HF and DF in a wide spectral range from 2.7 up to 4.8 µm are determined in experiment and also by numerical modeling.
The problem of the increase of the energy conversion efficiency of a broadband CO2 laser amplifier with optical pumping by the multi-frequency HF-laser radiation is considered. To improve the utilization of the pumping radiation and to broaden the amplifier bandwidth the use of a buffered with Xe mixture of the isotopomers of carbon dioxide and nitrous oxide as active medium is proposed. Experimentally and by calculation the coefficients of an unsaturated absorption of 14N16O, 12C16O2 and 13C16O2 were determined on 19 lines of the pulsed chemical HF-laser which concentrate up to 60% of its total output energy. The estimations show that the application of a three-component mixture of these molecular gases enables to increase up to 30% the coefficient of the utilization of the pumping radiation at aperture about 10 cm.
The dependence of the specific energy of the high-pressure CO2 laser (4.1 and 11.1 atm) with the optical pumping on the resonator losses coefficient and density of the absorbed energy of radiation of the HF laser on transition P1(8) is studied. The maximal values of the specific (200 J/l) and the total (7 J) radiation energy of the high-pressure CO2 laser (11.1 atm) are obtained with coefficient of transformation of the pumping radiation energy ((lambda) equals2.78 micrometers ) to energy of the CO2 laser radiation ((lambda) equals10.6 micrometers ) being equal to approximately 19% (quantum yield approximately 73%), and with parameter of excess of the unsaturated gain (g0equals0.1 l/cm) above the lasing threshold (gt) m equals g0/gt approximately equals 4.
The results of experimental study and numerical modeling of the high-power photoinitiated pulsed chemical DF/HF lasers operating in modes of free-running and amplification in the cascade scheme 'master generator (MG)- amplifier (A)' are presented. The comparative analysis of the laser operation efficiency for these modes with the object of obtaining maximal energy characteristics and radiation brightness is carried out. The maximal specific energy of 40 - 50 J/l and the maximal total energy of 2.9 - 3.1 kJ at divergence of 10-3 radian are obtained in free-running mode for DF- and HF-laser and values of 12 J/l and 290 J respectively are obtained at divergence of 8 X 10-5 radian for HF-laser. In mode of MG - A it is obtained in experiment 37 - 42 J/l, 2.9 - 3.4 kJ. On the base of numerical simulation it is possible to make a forecast as 60 J/l, 10 - 20 kJ and 5 X 10-5 radian with efficiency > 50%.
For the grounding of the program of the wide-aperture several THz bandwidth CO2 laser amplifier creation it was initiated the experimental investigation of a HF laser radiation transformation in a multiatmospheric C02/He medium. The C02/3He mixture (46x50x63 mm3, 4 atm) was pumped by the 1P8 spectral line of the pulsed chemical HF laser (85 J, 1 ps). Transverse pumping geometry was used. Up to the power density of 2.7 MW/cm2 an absorption saturation was not observed. At the deposited energy of 58 J and output coupling of 20% it was obtained CO2 laser pulse of 2.7 J (quantum efficiency was about 1 8.6%). The estimated small-signal gain was of 0.05 cm1
The cascade scheme "master generator Ñ amplifier" of the photoinitiated pulsed chain chemical HF/DF-laser is investigated by numerical modelling and in experiment. The possibility to control the duration and spectrum of the laser pulse is shown, the efficiency of amplifier can exceed the efficiency of the equivalent generator.
As a result of the theoretical research the possibility to control the laser pulse length of the chemical HF/DF laser in a range from the part up to some hundreds of microseconds by means of the variation of the laser medium density and the photoinitiation intensity by two orders of magnitude is shown. At that the specific energy characteristics of the active medium does not change essentially because of the variation of the chemical chain length under necessary condition of using the high-quality optical resonator. The calculations have shown that the specific output energy varies from 100 up to 300 J/g and the physical efficiency from 2,000 up to 18,000%. The laser pulses with length from 2 up to 45 microsecond(s) are obtained in experiment for HF and DF laser with the technical efficiency of 10 - 50%, the pulse energy from 2.6 down to 0.1 kJ, the specific energy from 88 J/g (50 J/l) down to 10 J/g (2 J/l) without the fulfillment of the complete optimization. In experiment the mode of the high frequency radiation pulsation is registered with the length of a separate peak lesser than 10 ns and the period equal to the double time of the photon pass through the resonator.
Survey of results of experimental investigations of energy and spectral characteristics of open-cycle full-scale mock-up of CW supersonic e-beam sustained CO laser (SSCO-EIL) of 200 kW power and results of numerical investigations of the possibilities of increasing output power, spectral line selection, and Q-switched lasing of SSCO-EIL are presented. The possible influence of properties of SSCO-EIL on efficiency of several laser technologies is considered. It is concluded that unique energy and spectral characteristics of SSCO-EIL open ways to drastic expansion of areas of laser technologies both owing to the increase of efficiency of laser energy utilization, and owing to reduction of the energy cost.
The numerical investigation of the energy and spectral radiation characteristics of the supersonic e-beam sustained CO laser, operating in the repetitive Q-switched mode, is carried out. All calculations are executed for values of parameters of the e-beam sustained discharge, gas mixture, supersonic channel and optical resonator close to the corresponding values for the experimental CW mock-up of this type laser with output power of 200 kW. In the mode of the resonator quality modulation, the parameters of output radiation depend on frequency of the pulse repetition. For frequency range of 0.7 - 50 kHz the average specific energy per unit of the gas mass is 28% - 96% of the specific energy in CW mode, the peak power exceeds 6400 - 170 times the CW power, the laser pulse length at the half-height is 35 - 60 nanoseconds. The radiation spectrum has some tens lines in the wavelength range of (lambda) equals 4.9 - 9.0 micrometer.
The calculations of energy characteristics, operating regimes and dimensions of the discharge zone of the supersonic e-beam sustained CO laser are presented. Calculations have been carried out for the laser modules with a power up to 40 megawatts.
Ways of achieving extreme energy characteristics of pulsed DF/HF lasers were determined as results of theoretical and experimental (at energy up to 5 kJ) investigations of generator and amplifier. The close output energies of DF and HF lasers and higher efficiency of the cascade circuit relative to an equivalent generator were obtained.
KEYWORDS: Gas lasers, Mirrors, High power lasers, Energy efficiency, Resonators, Electro optics, Carbon dioxide lasers, Reflectivity, Gadolinium, Laser applications
For operating conditions of the high power supersonic e-beam sustained CO laser a numerical investigation of the energy and spectral characteristics of the first overtone generation is conducted. It is shown that electro-optical efficiency of the first overtone generation can be more than 30%. The efficiency of a spectrum selection both on fundamental and first overtone transitions is evaluated. On the basis of numerical calculations the engineering evaluations for several variants of such a device are executed.
The results of the experimental and theoretical DSPIL modeling are presented. The parameters of the generation pulse (energy, duration, delay time) are measured for the series of perfluoriodide laser compounds under pumping conditions imitating the space solar radiation spectrum. The time dependence of the radiation spectrum was measured for the pumping pulse. The spectrum of this pulse corresponds to the ABB spectrum with temperature 6000 K in the pulse beginning and 3500 K in the end. The generation energy ratio (E10/E1) in repeatedly pumping pulse action without the active laser medium change was measured in this experiment. The empirical linear dependence between quantities 1n(E10/E1) and 1n(k3/k4) is received, where E1 and E10 are the energies of generation pulse after first and tenth pumping pulses. The mathematical model of DSPIL, containing the main kinetical processes description, is developed. The computing evaluation of the energy characteristics of DSPIL are presented.
During the reaction H(Dz)+F2 similar quantities of the chemical interaction energy are spent on the excitation of vibrational and rotational levels of 1W and DF molecules. However the known energy characteristics of pulsed chemical DF laser are 2—3 times lower than those of the HF laser [1J. It is connected on opinion of various researchers with larger (as compared with hF) number of vibrational arid rotational levels of molecule I)F among which the energy of chemical reactions is distributed with smaller values of Einstein coefficients and rate constants of chain reaction. lt results in lower value of gain for majority of vibrational-rotationai transitions of DF molecule. Therefore for extraction of laser energy from active medium of DF laser an optical resonator with small losses is required.
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