Current status of recently proposed novel approach to inertial fusion energy technology, where phase conjugating
mirrors generated by stimulated Brillouin scattering are employed to take care of automatic self-navigation
of every individual laser beam on injected pellets, has been reviewed. This new technology is of a particular
importance to the direct drive schemes of pellets irradiation as assumed, e.g., in HiPER project. If successful
also in its full scale realization, such an aiming scheme would greatly reduce the technical challenges of adjusting
large and heavy optical elements on each shot in a system with a repetition rate of at least several Hertz. In the
gradual step-by-step tuning of this technology, in this paper a close attention has been payed to the unconverted
basic harmonic issue with a special Faraday isolator design proposed.
Evidence from experimental measurements of the temporal duration Δ<i>t</i> of x-ray lasing and measurements or estimates of the frequency bandwidth Δν show that the Fourier transform limit Δ<i>ν</i>Δ<i>t</i> ~ 1 has been approached in several experiments. It is important to understand and quantify this fundamental limit. The temporal behaviour of x-ray laser pulses of short duration at the Fourier transform limit is examined in this paper. Using numerical methods to model ASE output, the behaviour of the electric field with time E(<i>t</i>) is determined from the Fourier transform of the electric field variation with frequency E(<i>ν</i>). The expected time-bandwidth product is then presented for different gain length products.
Results from PALS facility laser-massive Al target interaction experiments are reported. Main attention is devoted craters formation under the action of laser pulses of various energy (from 100 J up to 600 J), intensity (from 10<sup>13</sup> W/cm<sup>2</sup> up to 10<sup>15</sup> W/cm<sup>2</sup>), laser wavelength (0.438 μm and 1.315 μm), and focal beam radius (from 35 μm up to 600 μm). Crater replicas were made of wax and their depths and radii were subsequently obtained by microscopy measurements. Duration of the laser-pulse-initiated shock wave propagation into the targets was much longer than that of the laser pulse itself (400 ps). This was an important feature of the experimental arrangement. Theoretical model of the post-pulse crater formation by the shock wave propagating and decaying in solids after the end of the laser pulse is presented and applied for explanation of the results obtained in experiments.
Interactions of PALS iodine laser beam with low density porous targets and porous targets with Al foil attached to the rear side were studied using multi-frame interferometry and shadowgraphy. Electron density profiles at the front and the rear side of the targets were reconstructed from interferograms. Velocities of Al-foils accelerated by the pressure of the heated porous material were established from shadowgrams. A good symmetry and absence of local perturbations were observed both in the rear side plasmas of porous targets and in the shape of the accelerated Al-foils. Measured rear side velocities are in a good agreement with the presented theory of laser interactions with porous materials.
In this paper our new capillary discharge device built for the soft x-ray laser studies is described and the first experimental results obtained from electrical, optical and UV diagnostics together with code simulations are presented.
Interferometry measurements of zinc, copper and iron line plasmas created by the iodin laser PERUN ((lambda) equals 1.315 micrometer, (tau) approximately equals 400 ps FWHM) with intensities equivalent to those generated by low-level prepulses in the collisional excitation soft x-ray lasers (5 times 10<SUP>9</SUP> minus 1.3 times 10<SUP>11</SUP> Wcm<SUP>-2</SUP>) are presented. The interferograms were taken with 4 and 10 ns delays with respect to the peak of the drive laser pulse using the third harmonic of the iodine laser ((lambda) equals 438 nm). Preliminary results of electron density profile reconstructions in the plane perpendicular to the line plasma axis are reported.
Results of an experiment aimed at a detailed characterization of line plasmas created by intensities equivalent to those generated by low-level prepulses in the collisional excitation soft x-ray lasers are presented. Electron density profile in the plane perpendicular to the line plasma axis, at times 4 and 10 ns subsequent to the laser pulse, time-integrated electron temperature and time-integrated lateral extent of the plasma were obtained. These parameters were studied for zinc, copper and iron plasmas created on slab target by approximately 400 ps (FWHM) pulses of an iodine laser ((lambda) equals 1.315 micrometer) giving rise to irradiances ranging from approximately 4.8 multiplied by 10<SUP>9</SUP> to approximately 1.2 multiplied by 10<SUP>11</SUP> Wcm<SUP>-2</SUP>.
In this contribution we outline our program aimed at obtaining an efficient soft x-ray laser at the wavelength 25.5 nm, using collisional excitation in a neonlike iron plasma. The goal of the research that we are pursuing is to develop a relatively small-scale soft x-ray laser that would be accessible for a variety of applications. A driver available for us is the laser iodine photodissociation laser system PERUN, providing on the order of 40 joules in on the order of 400 ps (FWHM) pulses at the fundamental wavelength 1.315 micrometer. Theoretical analysis based on Z-scaling as well as detailed computer modeling of neonlike Fe plasmas suggest driving energies of approximately equals 15 Jcm<SUP>-1</SUP> should be sufficient to generate high gain coefficients (up to 7 cm<SUP>-1</SUP>) on the J equals 0 minus 1 line at 25.5 nm. The modeling reveals that a 1.315 micrometer iodine driver is more efficient in producing J equals 0 minus 1 amplification in this moderate-Z system than a 1.06 micrometer Nd:glass driver. As optimizing of pumping conditions is imperative for the feasibility of the project, we have started our experimental effort by investigating plasmas analogous to those created by a small-level prepulse, i.e. by intensities ranging from approximately 5 multiplied by 10<SUP>9</SUP> to approximately 1.3 multiplied by 10<SUP>11</SUP> Wcm<SUP>-2</SUP>. Preliminary results of this study are discussed elsewhere in this Proceedings.
An Algorithm to compute the spacing of parallel fringes obtained from Digital Speckle Pattern. Interferometers (DSPI), based on. discrete autocorrelation calculations, is analyzed and experimentally verified_ It is found to provide sub-pixel resolution and is comparable with FFT analysis_ Experimental results confirm the algorithm performance_
An interferometric technique -- complex interferometry -- which enables recording of up to three sets of data into just one so-called `complex' interferogram is reviewed and its potential and limits are described. Possibilities of analyzing complex interferograms on personal computers are discussed.