Numerical investigations of multi-channel laser radiation focusing efficiency through the optically inhomogeneous medium at the phasing on the system output and in the target-in-the-loop technique based on stochastic parallel gradient (SPG) algorithm have been performed. The efficiency of focusing according to the ratio of Fried’s parameter to subaperture size has been investigated.
The results of imaging system resolution enhancement of the astronomical objects by using a Rayleigh laser guide star (LGS) have been presented. Correction of the distortions of stellar optical image has been performed by the adaptive optical system. The numerical simulation of registration of radiation from the Rayleigh LGS by a Shack-Hartmann wavefront sensor has been carried out. It has been shown that accurate calculation and subtraction of magnitude of the defocus and tip-tilts allows mitigating the reconstruction error concerned with the finite distance to LGS and the angular position of the telescope. It has been demonstrated in the experiment that angular size of the natural star Scheat decreases by 3 times at the use of Rayleigh LGS at range of 5 km.
The numerical simulation has been carried out concerning the determination of needed number of adaptive mirror’s actuators for the correction of phase distortions accumulated by the laser beam under its propagation through an airway. For this purpose, a set of wavefronts of the laser radiation passed through the airway has been registered by a Shack-Hartmann wavefront sensor. The stacked actuators’ response functions of 107- and 203-element adaptive mirrors have been experimentally determined as well. The dynamic range of adaptive mirrors’ actuators has been considered in the calculations. It is established that the 203-element adaptive mirror is not suitable for correction of the registered aberrations due to the limited dynamic range. Meanwhile by means of 107-element adaptive mirror it is possible to obtain a corrected laser beam with the Strehl ratio St=0.65.
Numerical studies of the phase correction of a laser beam passed the turbulent atmosphere by an adaptive optical system with a Shack-Hartmann wavefront sensor have been performed. Criteria for the correction efficiency have been obtained under different the spatial resolution of an adaptive mirror and the Shack-Hartmann wavefront sensor for various values of the Fried parameter.
The results of experimental works on creation of the closed-loop adaptive optical system intended for the tip-tilt wavefront correction have been described. The control unit with a high-speed microcontroller realizing the management by piezo-electrical stacked actuators of the tip-tilt corrector with the help of stochastic parallel gradient algorithm has been developed. The results of experiments on the dynamic wavefront tip-tilt correction at the system bandwidth of 2 kHz are reported. The basic characteristics of the closed-loop adaptive system are measured.
The results of experiments conducted on a laboratory setup of a fast adaptive optical system based on the use of FPGA as the main control element and a bimorph mirror as a wavefront corrector are presented. The adaptive system bandwidth ranged from a dozen Hertz to 2,000 Hertz. For independent control of the quality of correction the intensity distribution in the far field was recorded. It is shown that for a good correction of the wavefront the system bandwidth should be an order of magnitude higher than the upper boundary of the spectrum of wavefront distortions caused by turbulence. A comparison of the model and experimental data is also presented.
The results of experiments carried out on the installation of a fast adaptive optical system with a bandwidth of 1500 Hz are presented. Graphs of the spectral power and normalized energy of Shack-Hartmann wavefront sensor focal spot fluctuations are presented. Theoretical calculations and experimental data are compared. It is shown that in order to achieve a satisfactory correction of distortions caused by turbulence, the system operation frequency should be an order of magnitude higher than the maximum frequency of turbulent distortions.
The results of numerical simulations and experiments on the correction of turbulent distortions of a laser beam are presented. The experiments were carried out using an adaptive optical system with a bandwidth of 2000 Hz. It was shown that for effective correction the bandwidth of the adaptive optical system should be an order of magnitude larger than the bandwidth of turbulent distortions.
The algorithm of an optical vortex coordinates and topological charge detection is considered. In the algorithm a vortex is localized as a point of an interference fringe branching. With application of the algorithm interference patterns obtained in laboratory and numerical experiments are analyzed and characteristics of vortices revealed in corresponding examples are presented.
The sensing of phase front of the vortex laser beams has been carried out with the help of a Hartmann-Shack sensor. The
vortex beam is generated in the form of a Laguerre-Gaussian beam (LG0
1 mode) with the help of the special helicoidal
phase plates manufactured by the kinoform technology. The measured shifts of focal spots on the hartmannogram are
compared with the calculated shifts. From the measured wave front tilts the reconstruction of singular phase surface has
been performed with using the novel reconstruction technique. The phase surface reconstruction is demonstrated in the
case of distorted vortices as well. The correction of an optical vortex is undertaken in the close-loop adaptive system including
the bimorph deformable piezoceramics-based mirror.
The short overview is given of optical equipment developed within the ISTC activity for adaptive systems of new generation
allowing for correction of high-power laser beams carrying optical vortices onto the phase surface. They are the
kinoform many-level optical elements of new generation, namely, special spiral phase plates and ordered rasters of microlenses,
i.e. lenslet arrays, as well as the wide-aperture Hartmann-Shack sensors and bimorph deformable piezoceramics-
based mirrors with various grids of control elements.
New phenomenon predicted earlier - failure of phase conjugation at the stimulated Brillouin scattering (SBS) of focused
laser beams with screw dislocation of phase front (Laguerre-Gaussian vortex modes) - has been experimentally confirmed
Phase conjugation of vortex beams does not take place as a phenomenon because of failure of selection of Stokes mode
conjugated to laser one. It occurs since the SBS amplification coefficient does not depend on the laser field phase, and the
Stokes field does not "feel" how the laser phase helix is twisted. Therefore the amplification coefficients of a Stokes conjugated
mode and an analogous mode of opposite helicity are equal to each other. For example, in the case of a doughnut laser
LG01 mode the Stokes beam consists of a random superposition of a few modes including conjugated one. For rather
wide class of vortex beams (for example, in the case of a laser LG11
mode with two rings), a novel phenomenon takes place
that can be called as phase transformation at SBS. Its essence is in the fact that in Stokes beam a mode with regular phase
front is selected, which is orthogonal to laser mode at all. In the near-threshold SBS regime, this selected mode is close to a
principal Gaussian mode. At SBS of the vortex laser beam the generation of the vortex hypersonic wave takes place in the
SBS-medium so that the topologic charge in the system "Stokes wave+hypersonic wave" is equal to the charge of incident
laser wave.
F. Starikov, V. Aksenov, V. Atuchin, I. Izmailov, F. Yu. Kanev, G. Kochemasov, A. Kudryashov, S. Kulikov, Y. Malakhov, A. Manachinsky, N. Maslov, A. Ogorodnikov, I. Soldatenkov, S. Sukharev
The sensing of phase front of the vortex laser beam has been carried out with the help of a Hartmann-Shack sensor. The
vortex beam is generated in the form of a Laguerre-Gaussian beam (LG01 mode) with the help of the special helicoidal
phase plates manufactured by the kinoform technology. The measured shifts of focal spots on the hartmannogram are
compared with the calculated shifts. From the measured wave front tilts the reconstruction of singular phase surface has
been performed with using the novel reconstruction technique. The removing of phase singularity from an optical vortex
is demonstrated in the close-loop adaptive system including the bimorph deformable piezoceramics-based mirror.
In this paper we investigate anisoplanatism effect in human eye. We measured off-axis aberrations of eyes of several
subjects and also performed measurements of corneal and internal optics aberrations. Using the results of the
experiments we estimated anisoplanatism effect in human eye and developed human eye models reproducing on-axis and
off-axis eye aberrations and their distribution between optical elements of the eye.
The sensing of phase front of the vortex laser beam has been carried out with the help of a Hartmann-Shack sensor. The vortex beam is generated in the form of a Laguerre-Gaussian beam (LG01 mode) with the help of the special helicoidal phase plates manufactured by the kinoform technology. The measured shifts of focal spots on the hartmannogram are compared with the calculated shifts. From the measured wave front tilts the reconstruction of singular phase surface has been performed.
In the present report the possibility of singular points detections using a Shack-Hartmann sensor is described and the precision of the developed detection algorithm is estimated. Also the algorithms of a singular wave front reconstruction are analyzed. Two algorithms are considered and their properties compared. One of them was developed by D. Fried, its description was found in literature. The second algorithm was developed by authors of the report. The both algorithms were introduced into the software of the sensor and insured satisfactory quality of singular phase reconstruction. The precision of algorithms compared in numerical investigations as well in real laboratory experiments.
In the present report the possibility of singular points detections using a Shack-Hartmann sensor is described and the precision of the developed detection algorithm is estimated. Also the algorithms of a singular wave front reconstruction are analyzed. Two algorithms are considered and their properties compared. One of them was developed by D. Fried, its description was found in literature. The second algorithm was developed by authors of the report. The both algorithms were introduced into the software of the sensor and insured satisfactory quality of singular phase reconstruction. The precision of algorithms compared in numerical investigations as well in real laboratory experiments.
The algorithms for screening singular points of the phase gradient vector field are developed, where vector field components can be measured with a Shack-Hartmann wavefront sensor or shearing interferometer. Special attention is focused on the singular points that allow localization of optical vortices (wavefront dislocations). Determination of the coordinates and the topological vortex charges is of special importance in optical vortex interferometry, in operation of optjcal communication devices that encode information by means of optical vortices, and for reconstruction of phase distribution of optical beams that propagate in a medium with dislocations. On basis of numerical modeling, accuracy of the algorithm is verified, comparison with other algorithms executed, and its advantages and drawbacks are analyzed. Performance results are presented of the singular wavefront recovery algorithm, whose operating requirement is preliminary detection of optical vortex dislocations.
A vortex kinoform mode converter which transforms a zero order Hermite-Gaussian laser mode to first order Laguerre-Gaussian mode with screw phase dislocation has been demonstrated. The kinoform element imitating mathematical helicoid surface has been fabricated in fused silica substrate with using wet chemical etching. Conversion efficiency >90% for high power laser beams has been achieved in testing experiments.
A new algorithm of the dislocation localization is suggested. It is based on the analysis of projections field of phase gradients. Accuracy of the algorithm is verified by numerical simulation. Special attention is focused on the precision of singular points (wavefront dislocations) screening. The algorithm is evaluated with respect to others and its advantages and drawbacks are cleared up. The method described can be included in the software of the Hartmann's sensor and be used in the full-scale experiments. Also the original algorithm of phase reconstruction is proposed and its characteristics are estimated. This algorithm requires detection of dislocation coordinates so it should be used together with the algorithm of dislocation localization. In the paper the comparison is performed of the proposed algorithm with the well known Fried's algorithm. After that the phase reconstruction technique is included into the model of a typical adaptive optics system.
The phase front measurements of a vortex laser beam have been carried out with the help of a Shack-Hartmann sensor. The vortex beam is generated in the form of a Laguerre-Gaussian beam (LG01 mode) with the help of the special spiral phase plates manufactured by the kinoform technology. The measured shifts of focal spots on the hartmanogram are compared with the calculated shifts.
Fedor Starikov, Yu. Dolgopolov, A. Dudov, N. Gerasimenko, Gennady Kochemasov, S. Kulikov, S. Pevny, A. Shkapa, S. Smyshlyaev, Stanislav Sukharev, L. Zykov
Simulations of an explosively pumped two-stage photo-dissociation iodine laser with an SBS mirror at laser aperture 15 cm have shown a good agreement of calculation and experimental data on energy, laser power dynamics, brightness and Strehl number of output radiation. Calculations and experiments show that parasitic reflections of laser radiation from the windows of amplifiers and elements of the optical scheme are a reason that the brightness value is frequently less than maximum possible one. It is found that the input intensity should exceed 10-20 W/cm2 for eliminating the harmful effect of parasitic reflections on brightness. The brightness increasing is promoted as well by reducing the SBS threshold and displacing the second amplifier towards the SBS mirror at retaining a total length of the system. Under optimal conditions the maximal brightness reaches 1012 J/sr.
The results of 3D modeling and experimental investigations on the Ne-like Ge x-ray laser (λ=196 Å) on ISKRA-5 facility in RFNC-VNIIEF are presented. The divergence of amplified spontaineous emission (ASE) in a direction perpendicular to the target is about 10 mrad, and ASE beam deflection with respect to an optical axis is about 10 mrad. The experimental data are in good agreement with the results of 3D non-steady-state simulations using TRANS code. Calculations show that considerable rise of brightness and transverse coherence length can be achieved under half-cavity conditions.
Fedor Starikov, V. Atuchin, Yu. Dolgopolov, A. Kopalkin, Gennady Kochemasov, A. Manachinsky, A. Martynov, N. Maslov, V. Novikov, A. Ogorodnikov, I. Soldatenkov, Stanislav Sukharev
The development of an adaptive system for the transformation of optical vortex is undertaken. Content of work consists of generation of a vortex with preset properties, measurement of its wave front and its correction by means of an adaptive mirror. The first stage of work has been realized on formation a Laguerre-Gauss beam with the help of the amplitude diffraction gratings and special phase plates fabricated on kinoform technology.
The problem of beam quality and effective delivering of powerful COIL radiation by means of SBS technique is numerically investigated. It has been obtained that at amplification of hardly non-uniform laser beam in the COIL gain medium an SBS mirror is able to provide ideal quality of phase conjugation and phasing of output radiation in a fiber bundle.
The development of an adaptive system for the transformation of optical vortex is undertaken. Content of work consists of generation of a vortex with preset properties, measurement of its wave front by a Shack-Hartmann sensor and its correction by means of an adaptive mirror. The first stage of work has been realized on formation a Laguerre-Gauss beam with the help of the amplitude diffraction gratings and special phase plates fabricated on kinoform technology.
Fedor Starikov, Yu. Dolgopolov, A. Dudov, Natalia Gerasimenko, Gennadi Kirillov, Gennady Kochemasov, A. Kopalkin, S. Kovaldov, Stanislav Kulikov, Vladimir Ladagin, S. Pevny, A. Shkapa, Sergey Smyshlyaev, Stanislav Sukharev, L. Zykov
Results of simulations and experiments on a high-power double-pass explosively pumped photo-dissociation iodine laser (EPDL) with phase conjugation (PC) are presented. The laser system consists of a master oscillator, two exploding amplifiers with a working mixture 25 Torr C3F7I+125 Torr Xe and amplifier aperture of 15 cm, and an SBS-mirror. The SBS mirror consists of an angular selector of Stokes radiation, an ordered raster of small diffraction lenses, a main focusing lens, and an SBS cell. The calculation model and the computer code package take into account the actual three-dimensionality of space, transient effects at SBS, parasitic reflections of laser radiation from elements of the optical scheme, intrinsic amplified spontaneous emission of amplifiers, radiation losses in the optical path, non-uniformity of gain, and radiation refraction on optical non-uniformities of the active medium caused by a shock wave. In the laser system, an optimal configuration of the SBS mirror is used. It possesses unique properties if compared to the existing specimens of SBS mirrors. It stably gives a nearly ideal quality of PC at any level of SBS saturation, i.e. any reflection coefficient that has been confirmed by experimental laboratory investigations. As a result of investigations, a good agreement of calculated results with available experimental data has been demonstrated in energy, time dependence of power and Strehl number of output radiation. The considered EPDL has output energy of about 400 J and brightness of about 1012 J/sr. It has been found that with the increase of the flux density of an input signal from the master oscillator in the range 0.01-20 W/cm2 the brightness of EPDL output radiation increases as well whereas the full energy varies relatively slightly. It has been shown that parasitic reflections of laser radiation from the ends of amplifiers and elements of the optical scheme with a coefficient exceeding 10-7 considerably decrease the axial brightness of output radiation. In order to reduce the harmful effect of parasitic reflections on brightness the distance between amplifiers should be increased.
Here consideration is given to the influence of spherical aberrations, smooth within a beam that arise in the optical channel of laser setups on the quality of phase conjugation at stimulated Brillouin scattering (SBS). A numerical simulation of phase conjugation at SBS was conducted. It was approximated to real conditions and took into account such factors as transient processes, diffraction of radiation, 3D of the medium, reverse influence of Stokes radiation on laser radiation (SBS saturation). It has been obtained that aberration of defocusing type is dangerous from the point of view of a considerable decrease of the reflection coefficient and the phase conjugation quality both in the quasi-steady-state and substantially transient mode of SBS excitation.
The results of modeling and experimental investigations on the laboratory x-ray laser in RFNC-VNIIEF are presented. The computational model and TRANS computer code of transient amplified spontaneous emission (ASE) have been developed. The actual 3D medium, random polarization source, diffraction, refraction, gain with saturation, scattering by fluctuations of density can taken into account in the model. The 3D calculations of ASE in a Ne-like titanium x-ray laser with transient collisional excitation are presented. Results of experiments are described on Ne-like Ge x-ray laser realized at irradiation of the target by radiation of the ISKRA-5 laser facility. The quasi-steady-state ASE generation on 3p,J=0-3s,J=1 transition of Ne-like Ge (19.6 nm) is observed that is the first demonstration of c-ray laser in Russia in laboratory conditions. The divergence of ASE in a direction perpendicular to the target is about 10 mrad, and ASE beam deflection with respect to an optical axis is about 10 mrad. The experimental data are compared with simulation results.
Fedor Starikov, Yu. Dolgopolov, A. Dudov, Natalia Gerasimenko, Gennadi Kirillov, Gennady Kochemasov, Stanislav Kulikov, Vladimir Ladagin, S. Pevny, A. Shkapa, Sergey Smyshlyaev, Stanislav Sukharev, L. Zykov
A non-steady-state theoretical and mathematical model and a complex of computer codes have been developed for modeling a high-power double-pass explosively pumped photo-dissociation iodine laser (EPDL) with phase conjugation (PC) at SBS. The model and the complex of codes taking into account 3D of space consist of two blocks. The first block is devoted to detailed modeling of the SBS mirror consisting of an angular selector of Stokes radiation, an ordered raster of small diffraction lenses, a main focusing lens, and a SBS cell. The second block describes the dynamics of radiation in the laser system as a whole with using SBS mirror parameters calculated in the first block. The model takes into account parasitic reflections of laser radiation from the elements of the optical scheme, intrinsic amplified spontaneous emission of the amplifiers, radiation losses in the optical path, non-uniformity of gain, and radiation refraction on optical non-uniformities of the active medium caused by a shock wave. As a result of calculations an optimal configuration of the SBS mirror has been determined, possessing unique properties if compared to the existing specimens of the SBS mirrors. It stably gives a nearly ideal quality of PC at any level of SBS saturation, i.e. any reflection coefficient that is confirmed by experimental laboratory investigations. Modeling of the laser sytem with two amplifiers at working mixture 25 Torr C3F7I+125 Torr Xe and amplifier aperture 15 cm has been shown a good agreement of calculated result with available experimental data in energy, time dependence of power and Strehl number of output radiation. The considered EPDL has output energy of about 400 J and brightness of about 1012 J/ster. Calculations show that under rising the density flux of input signal from the master oscillator in a range 0.01-20 W/cm2, the brightness of the EPDL output radiation increase whereas the full energy varies relativley slightly. It is shown that parasitic reflections of laser radiation from the ends of amplifiers and elements of the optical scheme with a coefficient exceeding 10-7 considerably decrease the axial brightness of output radiation. In order to reduce the harmful effect of parasitic reflections on brightness, the distance between the ampfiers should be increased.
Fedor Starikov, Yu. Dolgopolov, A. Dudov, Gennadi Kirillov, Gennady Kochemasov, Stanislav Kulikov, Vladimir Ladagin, A. Manachinsky, S. Pevny, A. Shkapa, Sergey Smyshlyaev, Stanislav Sukharev, L. Zykov
A non-steady-state theoretical and mathematical model and a complex of computer codes have been developed for modeling a high-power double-pass explosively pumped photo-dissociation iodine laser (EPDL) with phase conjunction (PC) at SBS. The model and the complex of codes taking into account 3D of space consist of two blocks. The first block is devoted to detailed modeling of the SBS mirror consisting of an angular selector of Stokes radiation, an ordered raster of small diffraction lenses, a main focusing lens, and a SBS cell. The second block describes the dynamics of radiation in the laser system as a whole with using SBS mirror parameters calculated in the first block. The model takes into account parasitic reflections of laser radiation from the elements of the optical scheme, intrinsic amplified spontaneous emission of the amplifiers, radiation losses in the optical path, non-uniformity of gain, and radiation refraction on optical non-uniformaties of gain, and radiation refraction on optical non-uniformities of the active medium caused by a shock wave. As a result of calculations an optimal configuration of the SBS mirror has been determined, possessing unique properties if compared to the existing specimens of the SBS mirrors. It stably gives a nearly ideal quality of PC at any level of SBS saturation, i.e. any reflection coefficient that is confirmed by experimental laboratory investigations. Modeling of the laser system as a whole at working mixture 25 Torr C3F7I+125 Torr Xe and amplifier aperture 15 cm has been shown a good agreement of calculated results with available experimental data in energy, time dependence of power and Strehl number of output radiation. The considered EPDL has output energy of about 400 J and brightness of about 1012 J/ster. It is shown that parasitic reflections of laser radiation from the ends of amplifiers and elements of the optical scheme with a coefficient exceeding 10-7 considerably decrease the brightness of EPDL.
The stimulated Brillouin scattering (SBS) of focused laser beams with screw dislocation of phase front (Gauss-Laguerre vortex modes) has been numerically explored with allowing for transient processes, non-steady-state conditions, hypersound noise and an effect of Stokes field on laser field, i.e. SBS saturation. Calculations as well as an analysis on the basis of perturbation theory under near-threshold SBS conditions have shown that phase conjugation of vortex beams does not take place as a phenomenon because of failure of selection of Stokes mode conjugated to laser one. It occurs since the SBS gain coefficient does not depend on the laser field phase under the near-steady-state conditions, and the Stokes field does not 'feel' how the laser phase helix is twisted. Therefore (for example, in the case of a doughnut mode) the Stokes beam consists of a random superposition of a few modes including conjugated one. For rather wide class of vortex beams (for example, in the case of a laser mode with two rings), a novel phenomenon takes place that can be called as phase transformation at SBS. Its essence is in the fact that in Stokes beam a mode with regular phase front is selected which is orthogonal to laser mode at all. In the near- threshold SBS regime, this selected mode is a principal Gaussian mode. Calculations show that at SBS of vortex laser beam the generation of vortex hypersonic wave takes place in the SBS-medium. Its topological charge coincides with the laser beam charge in view of vortex-free structure of the Stokes beam.
Fedor Starikov, Yu. Dolgopolov, S. Kovaldov, Gennady Kochemasov, A. Kopalkin, Stanislav Kulikov, Vladimir Ladagin, Stanislav Sukharev, Natalia Gerasimenko
Using the most complete in literature physical model of the non-steady-state stimulated Brillouin scattering (SBS), the numerical study is carried out of phase conjugation (PC) in the SBS-mirror that consists of an angular selector of Stokes radiation, an ordered raster of small lenses, a main focusing lens, and an SBS-cell. The ordered raster with controlled varying of its parameters allows to perform the effective angular filtering of non-conjugated Stokes component, to reduce the local light loads, and to avoid the competitive nonlinear effects. An optimal configuration of such SBS-mirror has been determined. It has the unique properties as compared with the current SBS-mirrors. It fixedly yields the PC quality that is near to an ideal (the PC coefficient is about of or more than 95%) at the selector transmittance 50 - 70% and any level of SBS saturation, i.e. any reflection coefficient. In the SBS-mirrors of different types the high PC quality in the focused beams takes place at the high reflection coefficients only that is difficult to realize as a rule. The experimental data obtained at a Nd laser facility show the validity of the simulation results. The developed conception of SBS-mirror with unique properties can be applied for the improvement of wide class of industrial lasers.
Fedor Starikov, Yu. Dolgopolov, S. Kovaldov, Gennady Kochemasov, A. Kopalkin, Stanislav Kulikov, Vladimir Ladagin, Stanislav Sukharev, Natalia Gerasimenko
As a result of experiments and numerical simulation of phase conjugation (PC) in the SBS-mirror with an ordered raster of small lenses, its optimal configuration is determined that has unique properties as compared with the current SBS-mirrors. In current SBS-mirrors in the focused beams the high PC quality takes place at high reflection coefficients only that is often unachievable. The presented SBS-mirror fixedly yields the PC quality that is near to an ideal at any level of SBS saturation, i.e. any reflection coefficient. The simulation results are in good agreement with the experimental data obtained for pulsed Nd laser radiation with using a super-clean SBS-cell and multi-level raster ofsmall Fresnel lenses.
Using the most complete in literature physical model of the non-steady-state stimulated Brillouin scattering (SBS), the numerical study is carried out of phase conjugation (PC) in the SBS-mirror that consists of an angular selector of Stokes radiation, an ordered raster of small lenses, a main focusing lens, and an SBS-cell. The ordered raster with controlled varying of its parameters allows to perform the effective angular filtering of non-conjugated Stokes components, to reduce the local light loads, and to avoid the competitive nonlinear effects. An optimal configuration of such SBS-mirror has been determined. It has the unique properties as compared with the current SBS-mirrors. It fixedly yields the PC quality that is near to an ideal (the PC coefficient is about of or more than 95%) at the selector transmittance 50 - 70% and any level of SBS saturation, i.e. any reflection coefficient. In the SBS-mirrors of different types the high PC quality in the focused beams takes place at the high reflection coefficients only that is difficult to realize as a rule. The first experimental data obtained at a Nd laser facility show the validity of the simulation results. The developed concept of SBS-mirror with unique properties can be applied for the improvement of wide class of industrial lasers.
The calculations of the phase conjugation at the stimulated Brilloiun scattering (SBS) of the laser pulse specific for such powerful laser facilities as NIF, MEGAJOULE, ISKRA-6 are carried out. A computer code based on the most complete in literature physical and numerical model of non-steady- state SBS is applied for this purpose. Transient processes and an effect of Stokes field on laser one (the laser pump depletion) are included. The possibility is demonstrated of obtaining the phase conjugation of the profiled laser pulse with temporal phase CPA modulation needed for ICF experiments in order to replace an adaptive mirror in multi- pass laser scheme by an SBS mirror. The laser spectral line width is greatly larger than the SBS spectral line width. It is obtained that the phase conjugation of broad-band laser focused beam with the complicated temporal power profile is feasible. When a minimal laser coherence length scale (dealt with an inverse width of spectral line) is more than or of order of a beam waist length, the Stokes beam is characterized by the high phase conjugation quality that is about 97%. At the enhancement of the laser modulation frequency, when the coherence length is shorter than the beam waist length by 10 times, the phase conjugation fidelity reduces to 80% and the SBS threshold rises.
The numerical study is carried out of amplified spontaneous emission (ASE) in an x-ray laser. Its gain zone appears in the laser-produced plasma at the prepulse irradiation of a thick optimally bent target and is characterized by an asymmetrical profile of the electron density. An effect of ASE transverse spatial coherence improvement is particularly investigated that takes place as a result of potential formation of a convex transverse density profile instead of a typical concave one. At the convex density profile one can obtain the partially coherent ASE whereas at concave density profile the ASE is practically non-coherent.
To achieve high compression of direct drive targets it is principally important to guarantee highly homogeneous illumination of the target. Compressions of approximately 104 require degree of homogeneity of 1 - 2%. It is suggested that in the high-power laser facilities being developed and projected now (Omega Upgrade, NIF, LMJ, Iskra- 6) various methods of intensity distribution smoothing will be used to achieve such homogeneity. In this report the efficiency of some smoothing methods is considered using 1D numerical modeling.
The formation of the amplified spontaneous emission (ASE) in the laboratory x-ray laser with the Markov fluctuations of the dielectrical permittivity (epsilon) is studied by the method of paraxial equation for the transverse correlation function of the radiation field. The fluctuations (epsilon) are found to impose a limit on the ASE spatial coherence and to decrease the power of the coherent ASE. In the case of the weak regular refraction, the ASE scattering by (epsilon) is analogous to the linear absorption and decreases the gain observed. At the strong defocusing refraction the effect of (epsilon) on the ASE has a 'latent' character: an essential fall of the coherence length is accompanied by a relatively small decrease in the axial intensity and by a small broadening of the ASE beam as a whole.
A calculational theoretical model of the recombination X-ray lasers has been developed describing the level population kinetics in an active medium. A comparison with the experiment shows that it describes correctly the main physical processes in such a laser. A scheme for calculating the angular spectrum of pulsed laser radiation is given and it is shown that it can be utilized for the description of experimental results.
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.