Search

Some effects of the interaction of Nd3+-glass laser, working in ordinary generation regime, with Armco-Fe surrounded by nitrogen in the pressure range (1–109) atm. have been investigated. Thephenomenon of capillary waves and the increase of the N2 content have been observed in the irradiated area. The mechanism of the laser light interaction with the metal is discussed in terms of plasma theory and X-ray analysis.

The intensities of the reflected second harmonic light from uniaxial KDP crystal immersed in an optically denser liquid 1-bromonaphthaline have been measured as a function of incident angles of the fundamental beam from a mode-locked Nd:glass laser. The results agree well with the theoretical prediction of Bloembergen and Pershan. We have observed the existence of a nonlinear Brewster angle in a transparent medium.

The onset of self‐focusing in a glass sample has been studied with a streak camera. After passing through the sample, the beam is no longer focused by a subsequent lens into a nearly diffraction‐limited spot, but rather into a time‐dependent ring. A simple model explains these results and indicates practical limitations for uniformly illuminating small targets with a Nd:glass laser chain.

By using a mode-locked Nd: glass laser with much improved beam properties, we have observed the onset of direct intervalence band absorption at 1.06 μm in germanium at excitation levels between 225 MW/cm 2 (≈2 mJ/cm 2 ) and 10 GW/cm 2 (≈75 mJ/cm 2 ). This absorption limits the transmission to a maximum value well below that expected for complete saturation of the direct valence-to-conduction band absorption coefficient by band filling.

Microexplosions induced by a Q-switched Nd: glass laser working above optical breakdown power density levels are able to destroy the inner wall of Schlemm’s canal and to tear open both the supraciliary and suprachoroidal space. Furthermore, the ciliary muscle bundles may be disrupted, becoming subsequently permeable to the aqueous and thus also acting as a new outflow route. However, whereas breaks of the inner wall of Schlemm’s canals are sealed in the monkey by the activity of endothelial cells forming a new Descemet membrane over the impact site, the supraciliary and suprachoroidal spaces remain open over an observation period of up to 480 days. Perfusion experiments with a HgS tracer substance have shown that these newly created, potential outflow routes may be considered as real additional filtration areas.

Volume compressions on the order of ${10}^{2}$ have been observed in glass microspheres heated by pulses from a Nd glass laser. The degree of compression is inferred from computer analysis of time-integrated x-ray photographs of the target plasma.

Rod amplifiers of 51-mm diameter and disk amplifiers with diameters of 51 and 86 mm were designed and some units have been built for use in a four-beam high-energy glass laser at the Los Alamos Scientific Laboratory (LASL). The design goals and measured characteristics of these amplifiers are discussed. Data on self-focusing damage in both rods and disks are presented. Important characteristics of capacitor-bank design, flashlamp construction, and laser glass are discussed. Completion of the four-beam system is scheduled for early 1974.

The first successful fabrication of a cryogenic foam target is reported. Detailed techniques to ensure accurate fuel loading in the foam shell are described. This target has been used for implosion experiments with the Gekko XII glass laser.

Non-resonant k-photon ionisation cross sections may be calculated by kth order perturbative treatment. This method is generally considered to be good when the detuning from the closest resonance is much larger than the expected shift and width of this resonance. The aim of this paper is to discuss the validity of this criterion for several realistic cases. By diagonalising an effective Hamiltonian built on a few quasi-resonant states, we have calculated multiphoton ionisation cross sections for ground state caesium by linearly polarised light in frequency ranges containing the tuning range of the ruby laser, the Nd glass laser and its first harmonic. The study is carried out up to an intensity of 1011 W cm-2.

This paper reports details on the design of the Nd: glass laser facility NIXE at the Central Institute of Optics and Spectroscopy, including the target chamber and the x-ray diagnostics, spatial and temporal behaviour of the 1.06 μm radiation generated are given. Plane, massive targets of aluminium and silicon have been irradiated with 6-nsec FWHM laser pulses. Investigations of laser produced Al- and Si-plasmas have been performed with spectral and spatial high resolution diagnostics, consisting of a 3 channel crystal-spectrometer, 2 crystal-microscopes, and 2 pinhole cameras and the results are presented. Line spectra have been interpreted within the hypothesis of a steady state coronal equilibrium. He-like lines of the Al-plasma indicate temperatures up to 400 eV and densities up to 2 · 1020 cm−3. Total x-ray photon flux in the He-like resonance line has been calculated giving 1013 phot/ster. Untersuchungen der Rontgenemission von Plasmen, die mit dem 6 nsec Nd:Glaslaser-System NIXE erzeugt wurden Es werden detailliert das Nd:Glaslasersystem NIXE des Zentralinstituts fur Optik und Spektroskopie einschlieslich der Targetkammer und der Rontgendiagnostik beschrieben. Das raumliche und zeitliche Verhalten der 1,06 μm Strahlung wird angegeben. Ebene, massive Al- und Si-Targets wurden mit Impulsen der Halbwertsbreite von 6 nsec bestrahlt. Die Untersuchungen der lasererzeugten Al- und Si-Plasmen wurden mit spektral und raumlich hochauflosender Diagnostik, bestehend aus einem 3-Kanal-Kristallspektrometer, zwei Kristallmikroskopen und 2 Lochkameras durchgefuhrt und die Ergebnisse werden vorgestellt. Die Linienspektren werden im Rahmen eines stationaren Koronamodells interpretiert. He-ahnliche Linien des Al-Plasmas weisen auf Temperaturen bis zu 400 eV und Dichten bis zu 2 · 1020 cm−3 hin. Der totale Rontgenphotonenflus in der He-ahnlichen Resonanzlinie ist zu 1013 Phot/sterad abgeschatzt worden.

The polarization-dependent gain of the three stages of a Nd: glass amplifier chain was measured. It was observed, for the first time, that a p-polarized input beam gave 20 to 30% higher gain than an s-polarized one under state of high inversion. This is explained on the basis of a polarization-inhomogeneity model for a stimulated emission cross section, coupled with a preferential gain recovery for a p-polarized beam as compared to an s-polarized one in a saturated Nd: glass amplifier.

The Institute of Laser Engineering at Osaka University outlines key issues of research, which are: the development of high-power drivers, pertinent pellet design for implosion by a large-scale computer code, pellet fabrication and handling, and diagnostic of the implosion process, with high resolution in space and time. Experimental facilities such as the GEKKO series and the CO/sub 2/-laser LEKKO series are discussed. A table and illustrations show energy drivers, the GEKKO XII optical arrangement, and the glass laser system of GEKKO XII. Fundamental processes in laser-plasma coupling, scaling of implosion presure, and implosion of the pellet and Cannonball target are described and accompanied by illustrations and photographs. The KONGOH project and activities at the Electrochemical Laboratory present research and progress on target experiments.

A significant effort has been made recently at CEL-V to improve laser facilities. OCTAL, the eight beam, 2 kJ laser, has been equipped with phosphate glass and KDP frequency tripling systems. PHEBUS, a two beam 20 kJ neodymium glass laser based on NOVA technology was denned and built and will be tested in early 1986 in close collaboration with Lawrence Livermore National Laboratory.In the field of diagnostics, the development of soft X-ray emission analysis has been emphasized.Most of the recent experimental results have been obtained at a short wave-length (0·35 μm). They deal with the effect of non-uniform illumination, 2D hydrodynamics with either plane or spherical targets, and the study of thermal transport inhibition.

The performance of an active-passive mode-locked and mechanically Q-switched Nd: glass laser is investigated. The mechanical chopper used for Q-switching reduces the temporal pulse train jitter. The acousto-optic modulator stabilizes the pulse trains. The wavelength tuning from 1048.5 nm to 1069.5 nm for a Nd: phosphate glass (Schott LG-703) and from 1056.2 nm to 1078.3 nm for a Nd: silicate glass (Schott LG 680) is achieved with a 5 mm thick single-plate birefringent filter.

The profiles of (3/2) ω0 emissions from planar targets of carbon, using a 20 J, 5 ns, Nd: glass laser, were obtained. At high laser intensities the profiles show a wavelength- and polarization-dependent intensity saturation. In the intensity saturation regime, the existence of a wavelength-dependent saturation domain, is reported for the first time. The observation of saturation phenomena at high intensities may be explained on the basis of onset of absolute two-plasmon decay instability.

Investigations of laser sparks in N2 and He produced by a mode-locked laser were made with the help of a streak camera. An expansion away and towards the laser depending on the gas pressure was found. The measured expansion velocity of the spark is described by a model based on a radiation mechanism.

Two anomalies have been observed in the emission of MeV ions from a gold target irradiated up to 2 × 1015 W cm−2 using a Nd:YAG:glass laser. These anomalies are shown to be consistent with self-focussing effects predicted by computer simulations. Details of the computer calculations are given.

The properties of the impulse coupling coefficient for long‐pulse Nd:glass laser irradiation to aluminum are reported. Most significant is an anticorrelation between this coefficient and the mass of the material removed by the irradiation. A model is suggested which shows that this property may be related to the convergence or divergence of the laser beam as it penetrates the material. When using long‐pulse irradiation, the impulse coupling coefficient does not depend on the initial conditions of the surface finish. Data are presented which also demonstrate the dependence of the impulse coupling coefficient on both the incident intensity and energy density.

A "halo" type laser system is presented whose radiation is characterized by a propagation planar beam rather than a unidirectional beam. A doubled Nd:glass laser mode-locked picosecond pulse train is used to pump a Rhodamine 6G dye solution filling a cylindrical closed resonator. The laser short pulse train propagates in a plane across 360°, with mrad divergence transversely to the propagation plane.

Performances of amplifiers, optical isolators and power supply system which constitute GEKKO XII Module high power glass laser system are described. GEKKO XII Module was developed during 1977-1979 and its remarkable laser characteristics were already published. A lot of efforts and various attempts had been made in order to obtain high components performances. The measured data not only satisfied specifications required for system operation, but also showed that those components were fairly cost-effective. Through the development of components, the designing and manufacturing techniques for high power glass laser components were sufficiently established and are expected to give technical bases for more scaled-up high power glass laser system; GEKKO XII System for KONGOH Project.

GEKKO IV glass laser system delivering output power of 4 TW in 100 ps and output energy of 2 kJ in 1 ns in 4 beams has been successfully developed. System design, major components, and operation of this laser system are described, and various aspects related to high power laser systems are briefly reviewed.

Actively initiated quasi-passive mode-locking has been achieved in a small-power CW SELFOC Nd:glass laser. Three means have been taken to enhance the pulse intensity incident on a saturable dye to a magnitude sufficient for nonlinear absorption initiation: 1) tight focusing, 2) controlled spiking oscillation, and 3) auxiliary active mode-locking. Mode-locked pulses having an 11-12-ps pulsewidth were obtained. Interpretation concerning the observed mode-locked-pulse intensity-correlation curves is presented. To obtain satellite-pulse-free mode-locked pulses, a modified mode-locking process with sufficiently long buildup time is considered.

In the paper some results of the studies on parameters of capillary waves generated in 18H2N4WA type steel by means of light pulses of Nd 3+ - glass laser with ultrasonic modulation of Q-factor of the optical resonator have been presented.

With a Nd-glass laser system, maximum focusable output power on a target is limitedby the beam breakup effect due to small scale filamentation.Spatial filtering is veryeffective in iemoving these small scale intensity ripples, and thus increasing the focusablepower.In this paper, we describe the design and construction of a vacuum spatial filterwhich is being used for the g1ass laser system Gekko II at Osaka University.Experimentalresults will be given on the transmittance chaiacteristics of the spatial filterand the improved performance of the glass laser system.These results will be analyzedin terms of the spectrum analyses of the intensity ripples.

The superbroadening of single 1.06 μm picosecond pulses extracted from a passively mode-locked Nd:glass laser in H 2 O and D 2 O has been studied. Data on ninety degree scattering of the laser pump and visible superbroadened (SB) light, the dependence of the SB light intensity on cell length, and the polarization ratio of the SB light are reported. The results show that filament formation and breakdown is not required to produce SB light, although these catastrophic effects may occur after the formation of SB light and occur concurrently with superbroadening at high laser pump intensities. The previous conclusion that four-wave parametric interaction is solely responsible for superbroadening in water is sustained by the present results. The present results show that to minimize self-focusing and to produce a highly polarized ps continuum beam for time-resolved spectroscopic study, low pump intensities and short cells should be used.

The use of CARS as a prove of gas phase molecular concentration has been extended into the picosecond regime. A double-beam configuration employing single pulses from a mode-locked Nd:glass laser has allowed measurement of N 2 ( 1 Σ g , ν = 0) pressures on accuracy of better than 10% with 8 ps time resolution. This technique shows promise for the study of dynamics of gas phase photodissociation processes.

Theoretical profiles of (3/2)${\ensuremath{\omega}}_{0}$ emissions from laser-produced carbon plasmas, at plasma temperatures varying from 600 to 250 eV, corresponding to laser intensities varying from 1.5\ifmmode\times\else\texttimes\fi{}${10}^{14}$ to 1.7\ifmmode\times\else\texttimes\fi{}${10}^{13}$ W/${\mathrm{cm}}^{2}$ have been calculated. The peak shifts of these emissions have been compared with the experimental results obtained using a 1.0641-\ensuremath{\mu}m Nd:glass laser and they are found to be in good agreement. Theoretical estimates of wavelength shifts taking into account the variation of plasmon wave number have also been compared with the experimental values. Profiles of (3/2)${\ensuremath{\omega}}_{0}$ emissions from planar slab targets of carbon, aluminum, and copper have been reliably measured and are compared with the theoretical estimates. Experimental results strongly suggest the saturation of two-plasmon--decay convective instability.

Breakdown in the rare gases caused by picosecond laser pulses from a Nd:glass laser is investigated. Threshold intensity for breakdown is measured as a function of pressure and measured values compared with those expected from theory. It is shown that an implicit assumption has been made in past theoretical treatments which may not apply on picosecond time-scales. Under certain conditions, this can lead to a multi-photon breakdown process which is density dependent. The experimental results are explained on this basis.

The electronic spectra following flash photolysis of chromium, molybdenum and tungsten hexacarbonyls were observed using an intracavity Nd 3+ -glass laser spectroscopic technique. The rotational structure of the spectrum of the 186 WO molecule has been analyzed.

A frequency doubled Nd glass laser was used to irradiate plane solid targets. Temporally and spectrally resolved measurements of the backscattered light were obtained together with calorimeter measurements of the backreflected energy. The results show the presence of stimulated Brillouin scattering and an estimate is made of the coronal electron temperature.

Intense ultrashort light pulses are generated i) by two-photon induced amplified spontaneous emission in a dye generator cell and ii) by two-photon induced seeding pulse amplification of a picosecond light continuum. The generated signals are amplified in a twophoton pumped dye amplifier. A passively mode-locked Nd: glass laser is used as pump source. Ligh pulses in the spectral region between 565 and 630 nm are generated in the dyes rohodamine B, rhodamine 6G, and PYC.

Technical, institutional, and financial assessments are made of inertial confinement fusion programs in the United States. Among the programs discussed are the Particle Beam Fusion Accelerator at Sandia, the AURORA facility at Los Alamos, the Heavy Ion Fusion Accelerator at Lawrence Berkeley Laboratory, the OMEGA glass laser system and facility, and the fusion research program at the University of Rochester. Target, diagnostic, heating, and other areas of research are discussed. Prospects for the future of fusion research within the context of the current energy scenario in the country are evaluated.

By using a perturbative treatment based on the central field approximation, the authors have calculated multiphoton ionisation probabilities in several cases of experimental interest (two-, three- and four-photon ionisation of the caesium and potassium ground states at the doubled Nd glass laser frequency and one-, two- and three-photon ionisation of some s, p, d and caesium Rydberg states). Some of these probabilities have been calculated beyond the minimum non-vanishing order. They have also performed some calculations for hydrogen. The comparison of their results with previous ones obtained by analytical methods provides a good test of the numerical techniques involved in the calculations.

A neodymium‐phosphate glass oscillator mode locked using the saturable absorber dye No. 3955 in a plastic host has been shown to give completely modulated outputs. Single pulses of duration ∼5 psec with the low background have been obtained, when operating close to threshold. The aperature time of the dye in the plastic host was measured to be 130±25 psec.

Direct measurement of pulse broadening in the second harmonic of a mode-locked Nd: glass laser has been made using a high-speed streak camera. Recorded pulsewidths varied from 3.8 psec to greater than 15 psec.

An energy capacitor charging technique was designed and tested for a Nd3+ doped glass laser system. The circuit is capable of delivering 19 J at 100 pps operation or 1.9 kW of power continuously to the flashlamp with a short burst capability of 140 pps operation. A dual in-line switching circuit composed of a water-cooled ignitron and a hydrogen thyratron tube with sequential grid drive is used in the energy capacitor charging system to assure flashlamp deionization. A simplified circuit approach which uses only one switching element is also discussed. A high system power efficiency of greater than 80% is possible with this latter approach.

Direct measurements with a picosecond streak-camera show that 1 mJ pulses, of transform limited durations ( Δt ∼ 3 psec, ΔtΔν ∼ 0.5), are produced at the beginning of the pulse train of a mode-locked Nd: glass laser. Pulse durations increase to ∼ 10 psec at the end of the train, with self-phase modulation frequency broadening. The optimum length of the contacted saturable absorber cell was found to be ∼ 50 μm , in agreement with earlier work using two-photon fluorescence measurements.

Spectrochemical analysis was studied with a Laser-microspectral-Analyser and a UV-Spectrograph. A Nd-doped glass laser (Output power was 1 Ws Max.) was used.The laser light was of normal pulse. BAM standard steels and some non-conducting powders (Spex Mix diluted with graphite powder, and SiO2) which were solidified with pure phenolic resin were then analysed.Electric discharge produced between auxiliary electrodes was used to strengthen the plasmas.Maximum sensitivity was determined for several elements and was found to be of the order of 10-13-14g.Plumes from metals, nonconducting materials and various other samples were photographed to know their location from the samples surface and the electrodes.The position of plumes from the sample surface in metallic samples was lower than in nonconducting samples.

It is observed that excitonic molecules in CdSe exhibit the Bose condensation when excitation is given at 1.8–4.2 K by pico-second light pulses from a mode-locked glass laser. Strong evidence is provided by the appearance of an extremely sharp luminescence line produced from the excitonic molecules condensed to the k = 0 state.

A short (30 μm) saturable absorber cell in contact with one of the cavity mirrors of an Nd:glass laser is found to be the optimum configuration for the production of short (2.5 - 8 psec) mode-locked pulses. The relationship between cell length and pulse duration is studied experimentally and theoretically.