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.
The picosecond CO2 gas laser has proven a valuable tool in strong-field physics applications. We review the merits of this approach, taking as an example, the Brookhaven Accelerator Test Facility (ATF) that affords a platform for exploring novel methods of particle acceleration and radiation sources. To carry out this mission, the ATF is equipped with a picosecond terawatt CO2 laser system, PITER-I. We describe the physical principles and architecture of this multi-stage laser system and its application in two high-energy physics projects. The first is the intense Thomson scattering of the CO2 beam from 60 MeV electrons with production of one x-ray photon per electron that opened the possibility for a Compton gamma-source generating a polarized positron beam for the next generation of electron-positron colliders, such as the International Linear Collider (ILC) and the Compact Linear Collider (CLIC). The second is our new study of a high-brightness multi-MeV ion- and proton-beam source energized by this picosecond CO2 laser. High-energy, collimated particle beams originate from the rear surface of the laser-irradiated foils. The expected advantage from using a CO2 laser for this application, rather than an ultra-fast solid state laser, is the 100-fold increase in the electron ponderomotive potential due to the tenfold longer wavelength of the CO2 laser. This innovation promises to substantially enhance energy efficiency and particle yield, and will facilitate the advancement of laser-driven ion accelerators towards practical applications. Finally, we address possibilities for generating CO2 laser pulses of petawatt peak power and a few-cycles duration.
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.
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.
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.
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 %.
An experimental study was carried out of pulse-periodic (rap-rate) operation of a CW chemical HF laser with optomechanical up to 103 Hz Q-switched cavity. Output pulse power shown increases at the experimental conditions no less than five-fold through the frequency region of 17-250 Hz. Average power of the rap-rate output reduced considerably comparatively to the same of CW mode operation, but shoot up with growing of the modulation frequency (in the same frequency region) faster than peak pulse power. It were discussed the possible causes of experimental and calculation characteristics differences of laser.
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.
To verify experimentally the possibility of effective conversion of multi-line pumping radiation of HF chemical chain laser by the use of a combined active medium on the basis of buffered with inert gas (He, Ar, Kr, Xe) mixture of various isotopomers of CO2 and N2O the energy and spectral characteristics of CO2-, N2O- and combined CO2-N2O lasers with optical pumping were experimentally studied. Pumping of dense mixtures (Ptotal = 11 atm) containing CO2: N2O: (He, Ar) = (0-1):(0-1):10 by cascade P1(8) and P2(7) lines of HF laser with total energy ≈200 J was performed. Specific input energy reached 2 J/cm3 at pump radiation fluence up to 10 J/cm2 and pulse duration of 1 μs. For the separate molecular components CO2 and N2O lasing with energies 4.3 and 8.9 J (input energies 47 and 104 J, respectively) in the spectral regions of (P- and R-) and P-branches was revealed. The CO2-N2O combined laser delivered emission with pulse duration ~ 30 ns in the region of overlap of R- and P-branches of N2O and CO2, respectively (wavelength 10.4 - 10.6 μm), with energy 12 J (200 J/1) equal to the sum of output energies on the individual components.
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%.
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.
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
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.
Influence of CO2 impurity within the laser medium on energy and spectral characteristics of the pulsed chemical chain DF-laser has been investigated experimentally. It is shown, that the mechanism of CO2 influence on the output laser characteristics and their sensitivity to CO2 concentration depends in a strong degree on lasing conditions. The influence of the CO2 molecule is determined only by relaxation processes and the sensitivity is minimal when the transition only between the low vibrational levels radiate in wavelength range of 3.6 - 4.2 micrometer due to low resonator quality. With low CO2 concentration and use of the high quality resonator the DF-laser generates on up to ten vibrational transitions in the wavelength range of 3.6 - 5.0 micrometer, thus the high efficiency of transformation of the reserved chemical energy in lasing is provided. In this case the CO2 influence on the DF-laser characteristics is defined both the relaxation processes and to greater degree the CO2 absorption in the range of 4.2 - 4.4 micrometer, and the sensitivity grows almost by the order of magnitude. On the basis of the investigations carried out the requirements to a degree of clearing of a laser medium from technological CO2 impurity for achievement of high specific energies of HF- and DF-lasers are determined [(CO2) less than 0.4 and 0.005%, correspondingly].
The aim of the present investigation is to forecast a principle opportunity of a pulsed DF to HBr laser frequency conversion and to evaluate an efficiency of that process. Computer modeling of the pulsed DF-HBr optical resonance transfer laser (DF-HBr ORTL) is performed and output characteristics of the system are predicted. The ORTL gas mixture contained DF at 10 torr, HBr at 10 torr and He at 100 torr. It was considered as a multiline pumping. The pump radiation flux was varied from 0.02 to 2 J/cm2. Depending on conditions the length of an ORTL gas media must be between 2 and 30 cm at using the longitudinal pump geometry. When DF- HBr gas mixture is pumped by a pulsed flash-initiated chemical DF laser, it is feasible to produce HBr lasing with a specific output energy over 100 mJ/cm3 and efficiency of 40% relative to absorbed radiation energy. When used for pumping, a pulsed electrical discharge chemical DF laser can provide HBr lasing with specific energy up to 20 mJ/cm3 and efficiency up to 25%. Therefore one will anticipate that a highly efficient laser system of the 4.2-5.2 micrometer spectral region can be developed.
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.
The influence of carbon-dioxide impurity within the laser medium on energy and spectral characteristics of pulsed chemical HF and DF lasers working on chain process has been experimentally investigated. An increase of the concentration of the carbon-dioxide impurity within the laser medium from 0.1 up to 0.6% caused the five-fold reduction in energy and in suppression of generation of about 50 spectral lines of six high bands. The sensitivity of the energy characteristics of the HF laser to the change of the carbon-dioxide concentration was an order of magnitude smaller than for the DF laser, in this case the appreciable changes in the HF laser spectrum were not observed. It is shown, that at low carbon-dioxide concentration (less than 0.1%) the achievement of equal specific output energies per HF and DF molecules is possible.
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.