The Asterix IV high power iodine laser was projected to deliver output pulse energies of up to 2 kJ at pulse lengths tp >= 1 ns in one beam. Using a mode-locked or a long-pulse oscillator the pulse duration can be adjusted in the range between 0.1 and 3 ns. In addition, in the fundamental wavelength at 1315 nm the laser can be operated at either the second or third harmonic at (lambda) equals 658 nm and (lambda) equals 438 nm, respectively. Up to now a maximum output energy of 1.3 kJ could be extracted which was -- at tp equals 0.4 ns -- limited only by the damage threshold of optical components. Emphasis has been put on improving the laser performance; e.g., the energy density of the top hat beam profile shows a modulation as small as +/- 6% and the output pulse energy can be kept stable within +/- 4% during a period of several months. Since 1988 the laser has been used for 3000 target shots and it has proved a reliable tool.
Numerical modeling of short pulse amplification in iodine laser requires a detailed enough theoretical model. This model must include: effects of deep gain saturation (gain cross section is high, (sigma) > 10-19 cm2, so in the great part of the amplifier chain (epsilon) pulse > (epsilon) sat); effects of finite gain bandwidth which are comparable with the pulse bandwidth; a complex structure of atomic iodine transition which consists of 6 components of hyperfine structure (HFS) and 36 sublevels of Zeeman structure (ZS); pulse deformations caused by passive shutters; transverse inhomogeneities of beam and amplifier characteristics. All these factors cannot be taken into account simultaneously. So we have developed a series of codes which model different aspects of pulse amplification in more or less detail.
Shock wave radiation allows us to pump quite large volumes and, therefore, to obtain iodine laser beams with high energy and power. In particular, previously we carried out experiments on the shock-pumped iodine laser with a beam aperture up to 1.2 m. Radiation energy up to 6 kJ in a single beam with a pulse duration of 3 - 5 ns has been obtained. In this work we investigate the dynamics of inversion space profile formation in the iodine laser pumped by the shock wave radiation.
The Institute of Experimental Physics has been investigating the application of SBS in high- power iodine laser since 1970. A short list of these works and the description of the most interesting experiments is presented here, both for short-pulse and free-running modes.
A fairly complex kinetic model was constructed to describe a free-running regime of iodine photodissociation laser at slow pumping. The slow pumping means that the pumping time is longer than the characteristic time of sound propagation across the cross-section of the laser tube, but the acoustic perturbation does not interfere with the inversion population inducing just the refraction index gradient. In this contribution the time variations of the refraction index are projected in the time dependent internal loss of the resonator, which renders temporal variations of the generated pulse or even a break in the generation. Internal loss modulation is derived from measured temporal development of active medium optical aberrations. The resulting free-generation pulse is compared with the measured one.
We present results of R & D of an iodine photodissociative pulse-repetitive flash-lamp pumped laser with average power approximately 500 W and discuss some problems of its efficiency and scaling. The main problems are follow efficiency of lamp pumping, energetic efficiency of iodine laser, energetic possibilities of active medium and its optical quality, and the closed loop of active medium. In conclusion, the energetic possibilities of developed pulse repetitive laser are discussed, as are some prospects for the near future.
An influence of the flashlamp ignition on the operation parameters was found. A metal stripe in the vicinity of the flashlamp tube leads to an increase of the flashlamp efficiency. The maximal increase of the UV signal in the region 270 nm of approximately 30% has been found. An explanation of this flashlamp behavior based on the contraction of the discharge channel is presented.
At VNIIEF laser fusion investigations are based on photodissociation iodine lasers (the wavelength of radiation (lambda) equals 1.315 micrometers ). The main goals of the investigations are determination of ignition conditions, choice of target types, laser interaction regime, energy and other necessary characteristics. Beginning in 1980 we conducted experiments on irradiation of targets of different types on the one-channel four-beam facility ISKRA-4 producing 10 TW. In the last years ISKRA-4 was upgraded: we realized conversion to the second harmonic and introduced the eight-beam irradiation system. Experiments at the second harmonic yielded 1 kJ of energy and 3 TW of power. In 1989 we built and put into operation the 12-channel facility ISKRA-5 producing energy up to 30 kJ and power up to 120 TW. In 1990 we began a series of target irradiation experiments on this facility. The present work is a review of laser fusion investigations conducted on the facilities ISKRA-4 and ISKRA-5. It contains a brief description of the facilities and of some specific phenomena which occur during monopulse amplification in high-power iodine lasers. Considerable attention is paid to problems of direct-drive targets and experimental results obtained on ISKRA-4 which are given in comparison with the data of model calculations. The work is concluded with the results of first experiments on irradiation of targets with a reversed corona which were conducted on the facility ISKRA-5.
A brief summary is given of some of the research in high power laser physics currently being performed in the United Kingdom. The survey is not intended to be comprehensive, and we have limited ourselves to highlighting a selection of topics of particular interest including plans for the development of short pulse laser systems, recent progress in x-ray laser research, and novel applications of laser-plasma x-ray sources.
We report about first experiments on plasma soft x ray production from solid xenon irradiated with (lambda) equals 1.315 micrometers light of the iodine laser ISKRA-4 at a pulse duration of (Tau) 0.5 equals 0.5 ns. It has been found that at laser intensities of q approximately equals (0.5 divided by 2) (DOT) 1014 W (DOT) cm-2 the main part of xenon plasma x ray energy corresponds to the quanta of energy in the range of 0.4 divided by 1.5 keV and the conversion factor (eta) reaches 10%.
Various regimes of interaction of ultrashort laser pulses with solid targets in vacuum are analyzed. Analytical formulas that characterize plasma parameters and x-ray emission during the laser pulse are obtained in a very broad range of experimental parameters. For constant laser energy, the conversion efficiency into x rays during laser pulse is shown to grow with laser pulse length in all interaction regimes.
Characteristics of several crystal spectrographs are analyzed on the basis of high-resolution spectra from laser-produced plasma. Using a tray tracing procedure, potential methods to optimize the experimental setup are indicated. Non-conventional applications of the double crystal spectrometer and focusing Johann spectrometer are discussed from the point of view of the highest spectral and spatial resolution, luminosity, and spectral range attainable.
Monochromatic x-ray imaging can deliver either two-dimensionally (2-D) space resolved or 1- D space and time resolved distributions of source emission, depending on the detector type. The spectral window of imaging is typically from 10-4 to 10-2 if 2-D bent crystals are used in the spectral range from about 0.1 nm up to 2.5 nm. A precision technology for bending thin crystalline wafers has been developed. Spatial resolution and crystal reflectivity have to be determined for each crystal. As an example, three time- integrated monochromatic x-ray images of two aluminum plasmas with a counterstreaming region are shown. They were obtained Hedelta, Hebeta, and Hegamma lines of Al ions with the help of a three channel x-ray microscope.
Comparative measurements of Si P-I-N diodes and thermoluminescent dosemeters responses to laser produced plasma soft x-ray radiation are reported. As dosemeters single crystals LiF:Mn,Ti TLD 100 and CaF2:Dy TLD 200 were used. It is demonstrated that an enhanced response of the Si P-I-N diodes is a significant effect in a region of high dose rates.
The second harmonic (SH) signal was monitored from a laser plasma created on an Al foil target by the pulses of an iodine photodissociation laser system. Both the time integrated spectra and the time dependence of the output from a narrow spectral interval in the vicinity of the SH were measured. For a p-polarized wave the spectra indicate regions of resonant absorption and of parametric turbulence. Interpretations of physical mechanisms underlying both the spectral regions are given. The dependence of the SH intensity on the incident laser power density is not clearly understood in all cases, but it seems to indicate a possible role of the plasma density scale length changing with the laser energy.
Three groups of ions were detected in Al laser plasma, produced by high power iodine laser PERUN with maximum power intensity of about 1015 W/cm2 on the target. The energy and charge carried by the ions were determined in dependence on delivered laser energy. The electron temperature Te in the range of 500 - 550 eV was evaluated within the laser energy from 1.5 to 25 J.
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.
C60 carbon clusters (fullerenes) were prepared by laser vaporization of a graphite target using a near infrared laser. A macroscopic amount of carbon deposit enabled us to apply the method of chemical extraction of C60 and its identification by UV spectrophotometry.
At VNIIEF work on chemical oxygen-iodine laser (COIL) was begun in 1982 at the Laboratory of Gas-Flow Chemical Lasers. The present report is a review of work performed at this laboratory, the same year generation at the 10 mW level was obtained. A year later the output power was increased up to 180 W. In 1986 optimization of the set-up operation allowed us to increase the laser power up to 900 W. Later a new research set-up was created. In 1990 it produced the output power of approximately 4 kW in 20 seconds.
The chemical oxygen iodine laser (hereafter referred to as COIL) has been attracting attention for its potential on the usage for material processing. The completion of the COIL for material processing with such systems as the fuel recirculation equipment, continuous water vapor trapping facilities, and so on, is informed. The suitable resonator design is investigated. The experimental test was carried out with the stable-unstable resonator and a high quality beam of near diffraction limit at the unstable side was achieved. Now, the possibility of the COIL for processing is actually ascertained.
The relaxation of electronically excited oxygen in the active medium of chemical oxygen- iodine laser (COIL) may cause a nonequilibrium population of O2 and I2. Previously it has been the subject of theoretical study. The authors of this study suggest that the vibrationally excited oxygen molecules of O2(1(Delta) ,v) may take part in the I2 dissociation. In this work the vibrational population of O2 molecules in the COIL active medium was calculated. The O2 vibrational populations are obtained under the typical lasing conditions. The gaseous medium of COIL consists of O2, O2(1(Delta) ), I, I2, H2O, Ar. It is assumed that the chemical generator of singlet-delta oxygen is used. In this case the molecules of H2O play the important role in kinetics of the vibrationally excited oxygen molecules.
By means of combined calorimetric and luminescence method chemical singlet oxygen gas generators in which alkaline peroxide solutio is replaced by solid peroxihydrate compounds were investigated; the operating principle of the generators is based on the interaction of powder peroxihydrates and gaseous chlorine or liquid chlorine containing reagents. The optimal composition of synthesized solid compounds allows hydrogen peroxide to be transformed into singlet oxygen with efficiency up to 100%. The usage of working solids in comparison with liquid ones has a number of advantages related to simplicity and safety in operation of such gas generators, significant consumption characteristic improvement and overall dimensions reduction, four times the increase in singlet oxygen yield per unit weight of working components, and water steam content minimizing in the gas stream at the gas generator exit.
The present work is devoted to the problem of scaling of bubbler-type SOGs and gas-transport system for COIL. The experiments were held on the experimental setup, which is described. It was the chemical singlet oxygen bubbler-type generator with a registration system. The concentration and content of singlet oxygen in the flow, and concentration of unreacted chlorine were measured. Also, the height of the gas-filled bed was fixed to obtain the propagation time of gas in the liquid
The injection and mixing of iodine vapor into a duct flow has been investigated experimentally and numerically. Laser-induced fluorescence has been used to visualize the progress of spreading of the iodine and its distribution homogeneity along the duct. Several injection methods, typical flow pressures for oxygen-iodine lasers, and various molar flux ratios have been examined to find the most favorable conditions for the mixing in supersonic lasers. A one-dimensional gasdynamic and kinetic computer model taking into account a zone of bulk type mixing with variable extension was used for estimating the influence of the mixing speed on the rate of dissociation and on the performance parameters of a supersonic oxygen-iodine laser.
Using the premixed isothermal model of the chemical oxygen iodine laser (COIL) the analytical expression is derived, which shows the dependence of power of the (COIL) on the parameters of active media, resonator and gas velocity. The two-dimensional numerical modeling of COIL was done in order to study the influence of mixing on the power characteristics of COIL. The results of calculations are compared with analytical predictions and experimental results.
Intense red emission was observed occasionally when a pulsed chemical oxygen-iodine laser was operated. The intensity of this emission was at least 100 times higher than any known emission of the oxygen-iodine system. The time history of the emission intensity indicated that it was pumped by the iodine laser. It seemed to be that the rust of the iodine injector was closely related to this emission. The decay time of the emission was measured to be 2 to 4 ms. The spectroscopic measurement revealed that the emission was identical with one that was found by Yoshida et al. and is being studied widely for a new candidate of a visible chemical laser.
Intensive Investigation and developmentof the chemically pumped Iodine laser has caused the creation by Kawasaiw of chemical oxygen Iodine laser (COiL) for material processing. The field of such a laser application could be widen if the pulse operation would be available. Such a regime allows to hightert the instant power of COIL with the average power being the same as for CW operation. The high instant power can be more preferable for such technological processes as drilling, cutting, ste.
Magnetic gain switching operation of a chemical oxygen iodine laser utilizing Zeeman effect on laser medium has been studied. This method is able to make a chemical oxygen iodine laser which operates in cw normally repetitive pulse laser. In order to obtain the largest ratio of peak power to cw power, experiments were carried out in this study. The wave form profiles of (pi) and (sigma) components divided with Zeeman effect were also investigated. Obtained ratio is the largest of 3.3 with cw power of 1 W. And it was found that (sigma) component contributed the pulse formation, when the polarization direction of output beam was not controlled.
A magnetic quenching of generation in a chemical oxygen-iodine laser (COIL) has been studied experimentally. This work gives data on a quenching threshold magnetic field in dependence on a resonator output coupling and an iodine concentration in the laser active zone, respectively. It was found that the threshold value of magnetic field was a decreasing function of the output coupling and an increasing function of the iodine molar flow rate. The normalized gain ((alpha) th/(alpha) ) is a decreasing function of the threshold field.
A theoretical model for an amplifier of pulsed chemical oxygen-iodine laser is presented. The calculation shows that the main point for obtaining high energy extraction efficiency is to let the oxygen-iodine laser beam emitted from an oscillator (1) have short pulse duration and high repetition rate, and (2) get multiple pass by mirrors through the excited medium within the oxygen-iodine amplifier.
The basic challenge in the design of a pressure recovery system for a supersonic gas laser arises from the fact that the cavity pressure is quite low: 50 - 70 torr for a CO2 gasdynamic laser (GDL) and as low as 4 torr for a chemical oxygen-iodine laser (COIL) system. The purpose of the pressure recovery system is to increase the pressure from its value in the supersonic cavity to one which allows the laser gas to be exhausted into the atmosphere. Two types of pressure recovery systems which are of primary interest for supersonic gas lasers are diffusers and ejectors. In this paper we derive some performance limits and examine the characteristics of both types of devices.