Laser spark obtained by using a conical optics is much more appropriate to form conducting channels in atmosphere. Only two types of lasers are actively considered to be used in forming high-conductivity channels in atmosphere, controlled by laser spark: pulsed sub-microsecond gas and chemical lasers (CO2, DF) and short pulse solid-state and UV lasers. Main advantage of short pulse lasers is their ability in forming of superlong ionised channels with a characteristic diameter of ~ 100 mkm in atmosphere along the beam propagation direction. At estimated electron densities below 1016 cm-3 in these filaments and laser wavelengths in the range of 0.5 - 1.0 mm, the plasma barely absorbs laser radiation. In this case, the length of the track composed of many filaments is determined by the laser intensity and may reach many kilometers at a femtosecond pulse energy of ~ 100 mJ. However, these lasers could not be used to form high-conductivity long channels in atmosphere. The ohmic resistance of this type a conducting channels turned out to be very high, and the gas in the channels could not be strongly heated (< 1 J). An electric breakdown controlled by radiation of femtosecond solid-state laser was implemented in only at a length of 3 m with a voltage of 2 MV across the discharge gap (670 kV/m). Not so long ago scientific group from P.N. Lebedev has improved that result, the discharge gap -1m had been broken under KrF laser irradiation when switching high-voltage (up to 390 kV/m) electric discharge by 100-ns UV pulses. Our previous result - 16 m long conducting channel controlled by a laser spark at the voltage - 3 MV - was obtained more than 20years ago in Russia and Japan by using pulsed CO2 laser with energy - 0.5 kJ. An average electric field strength was < 190 kV/m. It is still too much for efficient applications.
The possibility of developing compact all solid-state lasers for short-wavelengths based on laser
diode pumped single fluoride crystals is considered. The paper reviews our work and important data
from the literature.
The goal of the project is to accomplish a circle of experimental, theoretical works on creation of super-long conductive
canal technology for energy delivery from space. High repetition rate pulse-periodic laser system and the most important
components for the project realization are presented. Optical system and dust plasma based conductive canal idea for
long range energy delivery is discussed in details. Some experimental approaches for dust plasma conductivity tests and
new data of measurements are discussed. New applications of "Impulsar" program suggested technology are highlighted.
Basic characteristics of the laser-based engine will be compared with theoretical
predictions and important stages of further technology implementation (low frequency resonance).
Relying on a wide cooperation of different branches of science and industry organizations it is
very possible to use the accumulated potential for launching of nano - vehicles during the
upcoming years.
KEYWORDS: Reflectors, Pulsed laser operation, Molybdenum, Plasma, Wave propagation, Gases, Laser development, Medium wave, Chemical elements, High power lasers
Merging modes of optical pulsating discharge generated shock wave conditions are determined for the different parameters of gas pressure, energy and repetition rate of laser pulses. Quasi-stationary wave formation characteristics due to moving as well as stationary optical pulsating discharge for the cases of single reflector and matrix of reflectors will be discussed. Advantages of quasi-stationary wave mode for "Impulsar" engine applications will be demonstrated.
Conditions have been revealed, both theoretically and experimentally, where an optical pulsating discharge generates continuous periodical shock waves. It has been shown that this mechanism of shock waves merges into a low-frequency quasi-stationary wave operating in different gases (matter vapor) for a wide range of laser spark energies. The background for multi-megawatt laser based "Impulsar" engine will be presented.
The problems ofcreation the new media for solid state lasers of UV and VUV region are considered. The possibility
to widen of choice of laser's media for region from 120 to 350 nm are reported. The possibles to create UV and
vUv solid state lasers are discussed. This report is review on materials ourselves works and literature's data.
Merging modes of optical pulsed discharge generating shock waves conditions are determined for the different parameters of gas pressure, energy and repetition rate of laser pulses. Quasi-stationary wave formation characteristics due to moving as well as stationary optical pulsating discharge for the cases of single reflector and matrix of reflectors will be discussed. Advantages of quasi-stationary wave mode for Lightcraft engine applications will be demonstrated.
A technique for obtaining a pulse-periodic operating mode of high-power wide-aperture lasers (GDL, HF/DF, COIL) was put forward theoretically and experimentally realized for the case of GDL. The possibility of realizing a pulse-periodic mode in high-power wide-aperture lasers without a sacrifice in average output power was experimentally demonstrated and applicability of the realized approach for lightcraft technology further development is pointed out. Regime of light supported detonation wave and effect of shock waves joining for this particular application were investigated.
A technique for obtaining a pulse-periodic operating mode of high-power wide-aperture lasers (GDL, HF/DF, COIL) was put forward theoretically and experimentally realized for the case of GDL. The possibility of realizing a pulse-periodic mode in high-power wide-aperture lasers without a sacrifice in average output power was experimentally demonstrated and applicability of the realized approach for lightcraft technology further development is pointed out. Regime of light supported detonation wave and effect of shock waves joining for this particular application were investigated.
The feasibility of producing a continuous laser spark (CLS) with low resistance by focusing radiation from a CO2 laser with a conic mirror is demonstrated. The laser energy input per unit length required for this is experimentally found to be equal to 200 J/m. The possibility to efficiently control the trajectory of an electric discharge by means of a CLS is demonstrated. The effect of polarity in the electric breakdown of the air gaps between the CLS plasma channel and a metal rod is discovered and interpreted. The transverse structure of CLS conductivity is investigated. The possibility of producing a long laser spark (LLS) with much higher resistance by focusing radiation from a CO2 laser with a spherical mirror used to protect objects against lightning is studied. The conditions under which the electric discharges from clouds can be guided reproducibly along a LLS are determined. Experiments reveal that the interaction between the LLS and the discharge from an electrode (lightning rod) leads to a decrease in the lifetime of the streamer corona burst, as well as to an increase in the current of the developing leader and its velocity compared to the case without the LLS.
The feasibility of producing continuous laser sparks (CLSs) with a resistance per unit length of 100-400 Ω/cm by focusing radiation from CO2 laser with a conical mirror is demonstrated. The laser energy input per unit length required for this is experimentally found to be equal to ~200 J/m. The possibility to efficiently control the trajectory of an electric discharge by means of a CLS is demonstrated. A CLS is found to be an analogue of a high-conductivity metal rod during the electric breakdown and electric potential transfer. The effect of polarity in the electric breakdown of air gaps between the CLS plasma channel and a metal rod is discovered and interpreted. The transverse structure of the CLS conductivity is investigated. Most likely the CLS conductivity at the initial state is due to the photoionization of air by the radiation of primary nuclei of the optical breakdown.
This paper reports on the physics of a self-sustained volume discharge without preionization, self-initiated volume discharge (SIVD), in working mixtures of nonchain HF(DF) lasers. Dynamics of SIVD in discharge gaps of different geometry is thoroughly described. The mechanisms of restricting current density in a diffuse channel in electric discharges in SF6 and SF6 based mixtures determining the possibility of the existence of SIVD were suggested and analyzed using simple models. It is shown that the most probable mechanisms are the electron impact dissociation of SF6 and other mixture components, electron-ion recombination and electron attachment to vibrationally excited SF6 molecules. Starting from a comparison analysis of the rate coefficients of these processes, it was found that the electron-ion recombination is capable of compensating for electron detachment from negative ions by electron impact. It is established that SIVD can be observed not only in SF6, but in other strongly electronegative gases, e.g., in C3F8 and C3HCl3. Analysis is given of the factors determining uniformity of active medium in nonchain HF(DF) lasers. Some special features of operating nonchain HF(DF) lasers with small, 2÷6cm, apertures are carefully examined and the results of measuring the nonchain HF(DF) laser divergence are presented. Consideration is given to the problem increasing the aperture and discharge volume of nonchain HF(DF) lasers and, based from the experimental results, the possibility is shown of increasing their energy to a level of ~ 1kJ and above.
Current status of CO2 laser system “Picasso-2” intended to generate 10 μm pulse train with tunable pulses duration 2÷100 ps, interpulse separation ≈ 10 ns and train’s peak power over 1 TW is reported.
This paper reports on the physics of a self-sustained volume discharge without preionization, self-initiated volume discharge (SIVD), in working mixtures of nonchain HF(DF) lasers. Dynamics of SIVD in discharge gaps of different geometry is thoroughly described. The mechanisms of restricting current density in a diffuse channel in electric discharges in SF6 and SF6 based mixtures determining the possibility of the existence of SIVD were suggested and analyzed using simple models. It is shown that the most probable mechanisms are the electron impact dissociation of SF6 and other mixture components, electron-ion recombination and electron attachment to vibrationally excited SF6 molecules. Starting from a comparison analysis of the rate coefficients of these processes, it was found that the electron-ion recombination is capable of compensating for electron detachment from negative ions by electron impact. It is established that SIVD can be observed not only in SF6, but in other strongly electronegative gases, e.g., in C3F8 and C3HCl3. Analysis is given of the factors determining uniformity of active medium in nonchain HF(DF) lasers. Some special features of operating nonchain HF(DF) lasers with small, 2 divided by 6 cm, apertures are carefully examined and the results of measuring the nonchain HF(DF) laser divergence are presented. Consideration is given to the problem increasing the aperture and discharge volume of nonchain HF(DF) lasers and, based from the experimental results, the possibility is shown of increasing their energy to a level of approximately 1 kJ and above.
For the first time three-wave interaction of picosecond pulses was investigated as difference frequency generation with Ag- GaSe2 crystal. Group velocities and radiation absorption were taken into account during spectral analysis realization. Calculations were executed for CO2 laser parameters: 100 divided by 5 ps, 15 divided by 150 GW/cm2. Spectral characteristics and pulse power versus crystal length are represented for difference wavelength 800.5 micrometer.
Victor Apollonov, Vadim Kijko, Alexander Prokhorov, A. Suzdaltsev, Yu Vagin, V. Guterman, V. Rachuk, G. Zavision, P. Zhuravlev, V. Fedotov, A. Ivanov, A. Koroteev, Y. Svirchuk
Considered is recent progress in development AMT GDL Ña high power ~100 kW CW) C02 highly mobile industrial laser of wide application. Substantiated are general composition scheme of AMT GDL and choice of prototype engine for power unit of AMT GDL.
CO2 laser system generating the train of ~200 ps pulses with total energy up to 5 J was put in operation in General Physics Institute of Russian Academy of Sciences (IOFRAN) recently. Initial ~100 ps 10.6 ?m laser pulse with energy 10 ?J was regeneratively amplified in 5 x 5 x 5 cm3 discharge volume X-ray preionized TB-CO2 discharge unit developed and manufactured in D.V.Efremov Scientific Research Institute of Electrophysical Apparatus (NIJEFA) in cooperation with JOFRAN. The results on upgrade of this unit towards obtaining 10 atm volume self-sustained discharge in C02:N2:He mixtures with reasonably high percentage of molecular gases are reported. Owing to this upgrade free running mode laser radiation energy B1 (when the unit was equipped with unstable telescopic resonator) at 6 atm was increased up to 22.2 J, which corresponds to specific energy extraction 5.4 J/l/atm and efficiency 4.5%. The estimated value of B1 from such a laser at 10 atm is 15 J. It corresponds to peak power of regeneratively amplified 2 ps 10 ?m pulse formed in master oscillator of laser system Ñ1.5 TW. Prospective of further upgrade of laser system using new 10 x 10 x 100 cm3 discharge volume 10 atm TE-C02 discharge unit which is under construction now in NIIEFA in the network of ISTC Project #1072 is discussed.
The paper studies a self-sustained volume discharge without preionization-self-initiated volume discharge (SIVD)--to excite non-chain HF lasers on SF6-C2H6 mixtures. Once initiated by a local discharge gap breakdown, SIVD is found to propagate then over the whole gap normally to the applied electric field through successively starting diffuse overlapping channels at a voltage close to the quasi- stationary value. With forming new channels, the current through those previously originated decreases. The volume occupied by SIVD tends to expand with increasing the energy released within the discharge plasma, whereas a discharge bounded by a dielectric surface shows a simultaneous increase both in burning voltage and current. All these features combined allow a concept to be put forward of the existence of certain restriction mechanisms depending on the specific energy released and not permitting the total deposited energy to pass through a single channel. It is suggested that SF6 dissociation by electron impact and the electron attachment to vibrationally excited SF6 molecules are just those mechanisms. Simple analytical models have been developed allowing these mechanisms to be qualitatively described.
Highly efficient heat exchangers with uniform temperature distribution based on microchannel and porous structure are developed. The heat exchange efficiency dependence on construction peculiarities of the devices and cooling liquids properties are shown. Basing on the comparison of both experimental results and the numerical simulation, the ways to obtain the device thermal resistance about 0,2 C/W are discussed. Practical neededs for fabrication both linear diode arrays with power more than 1 kW will be observed.
In 7.7 divided by 39.6 cm1 range investigated for the first time refraction and absorption spectra of AgGaSe2 and AgGa1- xInxSe2 crystals allowed to compute a phase matching characteristic and efficiency values of difference frequency generation with total laser intensity from 60 MW/cm2 up to 15 GW/cm2. The maximum efficiency values were close to 1*10-3. Powerful half-cycle pulse generation is proposed with the investigated crystals.
Experimental investigation of small energy runaway electron beams for pumping of high power UV gas lasers was carried out. New approach of runaway e-beam generation with electron energy approximately 10 keV, current density greater than 103 A/cm2, at time duration of pulses 10-8 - 10-7 sec was proposed and realized. UV laser radiation with energy approximately 1 mJ under nitrogen pumping by runaway electron beam was obtained.
Amplification in free-electron lasers exploiting media with periodically modulated refractive indices is studied in the regime of a large modulation. The conditions for realization of the large-modulation regime in a layered plasma medium and in a periodic dielectric superlattice-like medium are established. The maximized gain, the corresponding saturation field and efficiency, as well as the optimal electron energy and propagation direction are determined and compared to each other for different types of modulated media. It is shown that the large-modulation regime makes it possible to extend significantly the operation frequency domain of the FEL employing a low-relativistic electron beam. Relationship with the Cherenkov and stimulated resonance-transition-radiation FELs is discussed.
The overview of the phase-locking problem for the powerful laser diode arrays is presented. Comparison of the external Talbot cavity configuration with the other ones is held. Attention is paid to both investigation and employment of the laser diode arrays consisting of wide aperture lasers. Such arrays, placed in the external cavity, allow easier solution of the scaling up problem that results in the output lobes with both significantly increased power and low divergence. Our experiments confirm feasibility of both QCW and CW phase- locking of the LDA in the external quarter-Talbot (Lc equals ZT/4) cavity at the output power of more than 10 W with the lobes divergence of (delta) (Psi) approximately equals 0.5 mrad. Employment of the efficient porous heatexchanger along with the system that cancels both induced phase distortions arising due to heat release and existing optical imperfections has allowed a breakthrough in powerful arrays phase-locking.
The results of principal upgrade of high-pressure, X-ray preionized TE-CO2 laser towards obtaining 10 atm volume self-sustained discharge in CO2:N2:He mixtures with reasonably high (up to 25%) percentage of molecular gases are reported. The estimated energy of radiation from such a laser is greater than or equal to 15 J. It corresponds to peak power of regeneratively amplified 2 ps 10 micrometer pulse formed in master oscillator of laser system greater than or equal to 1.5 TW.
Victor Apollonov, Alexander Bersh, S. Chdanovitch, P. Drozdov, Alexej Egorov, P. Egoyanz, V. Feofilaktov, Valerii Ikonnikov, Vadim Kijko, Victor Kislov, A. Lavrov, V. Malyavine, A. Suzdaltsev, Yu Vagin
KEYWORDS: Gas lasers, Combustion, Throat, Chemical reactions, Carbon dioxide lasers, Carbon dioxide, Chemical analysis, Carbon monoxide, Particles, High power lasers
At present, a mobile, self-contained laser rated at 50-70 kW or higher is required for solution of a whole range of urgent problems of technology and environment protection.
Results of current probe measurements for a plasma produced by the train of approximately 200 ps 10.6 micrometers laser pulses are reported. The train of pulses was obtained as a result of regenerative amplification of approximately 100 ps laser pulse in a 5 cm aperture 6 atm TE-CO2 laser. Experiments were carried out for Wo and Al targets dispersed in vacuum, two values of the interpulses separation in the train (Delta) T equals 9.3 and 29 ns and wide range of energy density on the target, corresponding to peak intensities of single pulses Ip equals 1 divided by 300 GW/cm2. Experiments had shown large difference of temporal structure of current signal with Wo and Al targets due to the considerable different in melting temperatures of these materials as well as radiation loses of laser plasma. We detected large ratio of current signal amplitudes for targets irradiation by the pulse train or gain switched pulse generated in TE-CO2 laser without injection of a short pulse. Results of these measurements are compared with those earlier obtained for nanosecond pulse train.
Scaling problems are considered for non-chain HF laser operating on mixtures of SF6 and hydrocarbons in which a chemical reaction is initiated by self-sustained volume discharge. The possibility of obtaining a volume discharge in SF6 and in corresponding mixtures without preionization, i.e., self- initiated volume discharge (SIVD) is a new qualitative result in solving the scaling problem for non-chain lasers. The dynamics of SIVD evolution has been investigated. The possibility of obtaining SIVD is determined in SF6 by mechanisms that limit the density of current, are related to specific energy release, and prevent the total energy from flowing through a single channel. A simple mode is developed for calculating the discharge characteristics in non-chain laser. The model provides a good agreement with experiment data. The obtained energy of nonchain HF-laser is 407 J and that of DF-laser is 325 J with the electric efficiency 4.3 percent and 3.4 percent, respectively. A possibility is estimated of creating non-chain HF lasers with the output energy of the order of kilojoules and higher on the basis of experimental data obtained.
A compact, solid-state, high-efficiency, and safe UV laser medical system with optical fiber output was created for treatment of destructive forms of pulmonary tuberculosis. A frequency-quadruped quasi-CW Nd:YVO4 laser system pumped by laser-diode array is investigated with various resonator configurations. A longitudinal end-pumping scheme was used in a compact acousto-optical Q-switched laser for producing stable pulses of UV radiation at the repetition frequency 10-20 kHz and the duration 7-10 ns with the fiber-guide output power exceeding 10 mW.
Using experiment data of laser damage threshold for ZnGeP2 surface we have made calculations of dependence of different frequency generation efficiency from nonlinear crystal length for different values of sum laser intensity (up to 10 GW/cm2) corresponding to definite CO2 laser types. Computation results showed that more 1-MW submillimeter power values are possible if to use sufficiently short powerful pump. These pulses are of considerable interest for many applications in matter investigations. Also we suggest to generate powerful laser half-cycle pulse at submillimeter wave region by means of difference frequency generation with ZnGeP2 and by converted radiation reflection and absorption switch on semiconductor wafers.
The overview of the phase-locking technique is presented. Analysis of the parameters that influence on the phase-locking is given. Admissible range of the deviation of the linear laser diode array, external cavity parameters is estimated. Comparison of the external Talbot cavity configuration with the other ones is held. Attention is paid to both investigation and employment of the laser diode arrays consisting of wide aperture lasers that opens an avenue to high power output radiation in a phase-locked mode. Special consideration is given to the cavity supermodes selection. Our experiments both confirm actual feasibility of 1D and 2D phase-locking of LDA's with specified parameters in the external Talbot (Lc equals ZT/4) cavity and illustrate theoretical predictions of the system stability and selectivity, so that: (1) phase-locking in 1D configuration allowed diffractional limited lobes width (delta) (Psi) equals 0.5 mrad; (2) tilting of the output mirror provided 'in-phase' supermode selection; (3) phase-locking in 2D configuration of the two LDA's of N equals 8 lasers, separated by 1600 mkm resulted in diffractional lobes full width at half maximum (delta) (Psi) equals 0.5 mrad in slow axis and (delta) (Psi) equals 0.25 mrad in fast axis.
Initiation mechanisms of self-sustained volume discharge (SSVD) are analyzed in mixtures of SF6 with hydro-carbons (deuterocarbons). The possibility is shown to obtain SSVD in a large volume of SF6 and hydrocarbon (deuterocarbon) mixtures without preionization in the discharge gaps possessing high edge nonuniformity of electric field. The scaling characteristics of nonchain HF (DF) laser are investigated. The highest generation energy has been achieved, namely, 397 J for HF laser and 312 J for DF laser at the electric efficiency 3.8% and 3%, respectively.
The construction of CO2 laser system generating a train of subnanosecond laser pulses with total train energy up to 5 J is reported. A record level of laser energy was obtained due to utilization of unique 5 X 5 cm2 aperture, 6 atm X- ray preionized CO2 amplifier. The estimations of individual pulses durations in the train are given. The prospective of upgrading of present configuration of laser system towards shortening of laser pulses duration and increasing the pressure of working gas mixture of the amplifier and its efficiency are discussed.
It is established that higher stability of a self-sustained volume discharge (SVD) without pre-ionization in mixtures of SF6 with hydrocarbons (deuterocarbons) is explained by higher surface density of cathode spots and the corresponding reduction of the current across a spot. It is shown that SVD may occur in mixtures of SF6 with hydrocarbons (deuterocarbons) without special systems for gas pre- ionization in extremely compact system of electrodes. Wide- aperture non-chain HF (DF) lasers with high radiation energy can be created on this basis. Such laser with the aperture approximately 20 cm provided the generation energy 190 J in the case of HF and 152 J in the case of DF and the electric efficiency 3 and 2.4 %, respectively.
KEYWORDS: Gas lasers, Carbon dioxide lasers, Laser cutting, High power lasers, Laser applications, Metals, Laser development, Industrial chemicals, Chemical lasers, Chemical oxygen iodine lasers
A brief comparison of various types of lasers of 50 - 100 kW power range for industrial use is presented, taking into account the most important technical and economic details. Listed is consumption of fuel, gas components, water, atmospheric air, also electric power required for some of lasers described. Its emphasized that the most prospective is high power laser of gas-dynamic type. It is featured by the outstanding weight-dimensions and specific characteristics. Essential advantage of the proposed gas-dynamic mobile laser is independence of stationary supply of electric power generally required for other types. Combined with independence of electric power plant, the totality of its technical properties, reliability and relatively low operation expenses makes it especially attractive solution of wide range of technological problems like worn reactors utilization, heavy- gauge metal cutting, thin oil films water pollution, etc., namely by means of autonomous mobile technological gas-dynamic laser (AMT GDL).
The overview of the phase-locking technique is presented. Analysis of the parameters that influence on the phase-locking is given. Admissible range of the deviation of the linear laser diode array, external cavity parameters is estimated. Comparison of the external Talbot cavity configuration with the other ones is held. Attention is paid to both investigation and employment of the laser diode arrays consisting of wide aperture lasers that opens an avenue to high power output radiation in a phase-locked mode. Special consideration is given to the cavity supermodes selection. Our experiments both confirm actual feasibility of 1D and 2D phase-locking of LDA's with specified parameters in the external Talbot (Lc equals ZT/4) cavity and illustrate theoretical predictions of the system stability and selectivity, so that: (1) phase-locking in 1D configuration allowed diffractional limited lobes width (delta) (Psi) equals 0.5 mrad; (2) tilting of the output mirror provided 'in-phase' supermode selection; (3) phase-locking in 2D configuration of the two LDA's of N equals 8 lasers, separated by 1600 mkm resulted in diffractional lobes full width at half maximum (delta) (Psi) equals 0.5 mrad in slow axis and (delta) (Psi) equals 0.25 mrad in fast axis.
The construction of CO2 laser system generating a train of subnanosecond laser pulses with total train energy up to 5 J is reported. A record level of laser energy was obtained due to utilization of unique 5 X 5 cm2 aperture, 6 atm X- ray preionized CO2 amplifier. The estimations of individual pulses durations in the train are given. The prospective of upgrading of present configuration of laser system towards shortening of laser pulses duration and increasing the pressure of working gas mixture of the amplifier and its efficiency are discussed.
This paper describes detailed analysis of optical and dielectric properties of ZnGeP2 crystals in middle IR and FIR spectral ranges, and also first experimental results on 1 W level 102 - 110 micrometers emission generation by means of difference frequency generation of CO2 laser line pairs. It is shown that MW level is achievable now, and AgIn0.35Ga0.65Se2 crystal can be used for efficient generation of FIR emission.
A pulsed radiation power of approximately 1 W was reached for the first time, with the aid of a ZnGeP2 crystal, at the difference frequency of CO2 lasers radiation in the submillimeter spectral range.
YSGG:Cr:Nd laser adaptive resonator, adjusted to laser rod thermooptical distortions by means of hydraulically controlled HR flexible mirror, was developed and investigated. Lasing with output power of 27 W and with more than twice improved divergence of 9 mrad was demonstrated during the thermal lens correction. A high optical quality metal flexible hydraulically-controlled HR mirror with a wide range of a focal length alteration is proposed to correct a laser rod thermal lens.
The purpose of our study is the development of the hardware and the software of a fast- response Hartmann sensor (HS), providing real-time measurements of the WF local tilts, expanding the WF in terms of the 19 low order Cernike polynomials, and estimation of the temporal and spatial WF statistics.
A number of important applications of high precision positioning actuator are related with laser technique and technology, optics, especially with large optical devices for the ground and space based astronomy. These actuators can be used in adaptive optics as the displacement and force actuators to preform in real time a mirror surface, conjugated with the wave front aberration by means of elastic deformation of mirror substratum [1,2]. A spring—type magnetostrictive actuator (STMA) in which Wiedemann effect (WE) [4] is realized, was described in [3] - is one of the interesting types of macro actuators, by means of which it is possible to achieve a precision displacement level 200 Lm with the accuracy of positioning up to 0.1 Lm in a real time scale ( up to 5 ms). Hence, the STMA satisfies all the visible and infrared adaptive optics requirements. A more complete understanding of such approach to actuators creation allows one to establish the main distinguished STMA features [5,6] : 1. High level of STMA relative longitudinal defomatins is controlled by STMA designed parameters and reaches 10 -10 when using ordinary magnetostrictive materials. This level of relative longitudinal deformations is accessible only for best sorts of piezoceramics; 2. A width of STMA magneto mechanical resonant frequencies band (from 10 Hz up to 1 kHz) is controlled by designed STMA parameters; 3. It is possible to use the inverse Wiedemann effect (IWE) for STMA material stresses controlling and, consequently, for closed loop STMA control.
KEYWORDS: Resonators, Mirrors, High power lasers, Solid state lasers, Beam controllers, Reflectivity, Deformable mirrors, Metals, Laser resonators, Disk lasers
Control of laser radiation characteristics using deformable resonator mirrors is considered on the basis of operator equation, which leads to several deterministic algorithms. Algorithms for control of unstable resonator loss, output intensity, and phase distributions are derived within the developed theory. In this framework, heat lens compensation in the Fabry-Perot resonator of a solid-state laser and control of output beam divergency is considered. For solving this problem a single-channel active mirror was designed and investigated. Active control of 60 W multimode repetitive-rate YAG:Nd3+ laser resulted in radiation brightness increasing with a 2 - 5 ratio and in energy distribution and mode structure improvement. Experimentally measured efficiency of control is in good qualitative agreement with developed theory.
Complete model of a multiactuator flexible mirror,made as a thin plate with discrete piezo-actuators is described. Experimental results validated the efficiency of proposed model are presented.New concept of adaptive optical system with flexible mirror and linear wavefront sensor is developed.
Development and creation of powerful technological lasers re- quires complex solution of problems of optics, quantum elec- tronics and thermal physics. The achieving of stable in time energetic parameters of technological lasers with cooled ele- ments of power (EPO) and adaptive (EAO) optics can be achieved only by a correct choice of their cooling modes, eliminating or compensating negative effects of heating EPO by laser radia- tion because of principal difference of reflectance of the mir- ror surface from I. The convective regime of EPO or EA0 coo- ling is mainly used in laser technique and carried out by pum- ping the coolant through a penetrable disperse compact heat ex- changer, on the work surface of which a thermally thin layer, separating radiation and the coolant liquid in heat changer, is made /1,2/. The intensity of heat transter and therefore, the degree of thermostatting of the reflecting surface of EPO are determined by a large number of design and technological factors not always reproducible in the EPO manufacturing. Ne- vertheless, for EPO, made on the basis of powder porous struc- tures, the level of removing heat fluxes reach 2 . 10' wt/cm2 under the thermal deformation of the mirror surface less than 1pm, the effective heat transfer factor for a heating mirror surface equal to r%, 105 wt/m2 . °C in this case /2/.
An analytical model of an active flexible mirror is described in which a thin plate with discrete piezoactuators comprises the proposed mechanism. The model of the adaptive mirror (AM) surface formation is given in terms of the thin-plate theory of the substrate's and actuator's elastic interaction. AM parameters are determined by means of the model as is a numerical simulation of the AM operation in an adaptive optical system (AOS). The AOS control algorithm utilizes orthogonalization of the wavefront sensor to overcome phase distortion in phase conjugation. A Hartmann-type wavefront sensor and a mirrorlike phase corrector with discrete actuators are considered in the numerical simulation of the phase-conjugate AOS. Compensation error in the proposed 19-channel hexagonal-array AM algorithm is found to be between 1.5 and 4 times higher than that required for optimal control in the case of Seidel aberrations.
A deterministic algorithm is outlined which controls resonator loss by means of profiling active resonator mirrors to control the laser output power from an active medium. The control algorithm is designed to meet two basic requirements: that it provide a range of resonator transparency which permits laser output power ranging from zero to the maximum output power level for initial unsaturated gains or a wide range of pumping rates; and that the reference resonator output beam's quality and transverse dimensions be preserved during output power control. A stationary phase approximation is used to study the active resonator, and numerical calculations are performed for an active resonator with controlled losses. The curvatures of the axial areas of active mirrors are found to contribute most to resonator loss. Two channels of control over the curvature of the axial elements of active resonator mirrors are found to be adequate in the algorithm for loss control. Unstable control regions are identified in the numerical modeling, and the algorithm permits the control of laser output power over a range of pumping rates.
Investigations of currents in close-to surface plasma, produced by CO2- laser radiation of different temporal structure have been carried out. The character of evolution of registered currents temporal structure at growing energy density was different when the target was irradiated in air and in vacuum by the train of short (τ= 2.5 ns ) pulses. Experiments in vacuum have revealed that the transit from smooth single mode pulse to the nanosecond pulse train of the same total energy was followed by a considerable decrease in plasma formation energy thresholds and by the increase of amplitudes of currents induced by plasma. The current pulses from the target were registered after finishing the laser irradiation; their appearance was probably connected with cumulation effects, caused by the ring form of the irradiated area.
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