Giant Pulse Laser Research Articles

Laser plasma generation from a deuterium ice pellet freely falling within a superconducting magnetic bottle

An experimental system is described for the production of an isolated plasma blob from a freely falling, isolated deuterium ice pellet by means of a high power giant laser pulse. A falling pellet which has dimensions ranging from 0.1 to 0.4 mm (with 5*1016-3*1018 atoms), is detached from the freezer head by gravity and is captured by the focused high power laser beam pulse after falling freely through about 10 cm. The plasma thus produced in a vacuum chamber is confined in a magnetic cusp or mirror field which is produced by a pair of superconducting coils.

Optical isolators for high-power giant-pulse lasers

Describes Faraday rotators acting as optical isolators, which are indispensable to experiments for producing plasmas with high-power giant-pulse lasers. Special attention is paid to the problem of material.

Origin of the Nonlinear Refractive Index of Liquid CCl4

We report here the first determination for a simple liquid (specifically liquid C${\mathrm{Cl}}_{4}$) of the fraction of its Kerr effect that arises from the (nearly instantaneous) nonlinear response of its electronic currents, and hence would exist even if the nuclei were frozen in position. To do this, we have remeasured the power dependence of the rotation of the polarization ellipse of a monochromatic beam in C${\mathrm{Cl}}_{4}$ with greatly improved accuracy (\ifmmode\pm\else\textpm\fi{} 10% absolute) using a single-Gaussian-mode ruby (giant pulse) laser. We then compare the results of this ellipse rotation measurement with existing Kerr data, and, using a general relation between the relative electronic contributions to both effects which we demonstrate, we show that (54 \ifmmode\pm\else\textpm\fi{} 16)% of the Kerr effect in C${\mathrm{Cl}}_{4}$ arises from nonlinear electronic response. The method should be useful for any isotropic material.

Tunable, spectrally bright near UV emission by the second harmonic of a dye laser

A tunable near UV laser with high spectral brightness has been constructed. A ruby giant pulse laser pumps a polymethene dye. The resulting IR emission is tuned and narrowed with two tilted Fabry-Pérot interferometers and a resonant reflector. This beam then generates second harmonic light in ADP or LiIO 3 crystals, in various configurations. Best result obtained from LiIO 3 externally: 16 mJ in a width of ≲ 0.005 nm.

Optical Bleaching and Deviations from Beer—Lambert's Law of Solutions Illuminated by a Ruby Laser. I. Cryptocyanine Solutions

The deviations from Beer—Lambert's law of solutions of cryptocyanine were measured when the solutions were illuminated by a giant ruby laser pulse. The transmission-intensity curves show quite unambiguously that a second absorption from an excited state is needed to explain the experimental results. It is also shown that under steady state conditions it is the number of absorptions and not the detailed level scheme that governs the behavior of the system. The transmitted pulse was shown to be narrower than the incident one in an amount depending on incident intensity. Using the two absorption steady state mechanism, the change of shape could be explained and calculated. The decay rates and absorption cross sections were calculated for two models—the one which assumes absorption from an excited singlet, and the other which assumes absorption from the lowest triplet state. The blue fluorescence of cryptocyanine is explained in terms of our results. A level scheme based on the known spectrum fits with the suggested model.

Investigation of Electrically Charged Liquid Jets

The behaviour of fine liquid jets is investigated with the help of microphotographs. Light pulses of 30 ns from a giant pulse laser were used for illumination to ensure sharp pictures. Using this arrangement the spontaneous and forced drop formation of the jets was investigated and found to be in good agreement with theory. Further, the behaviour of the drops during their flight through the air was determined for drops carrying different electrical charges. Special attention was given to trains of drops consisting of a varying number of drops as well as the coalescence of charged and uncharged drops. Explanations of the phenomena observed will be given.

Über die Entzündung eines n-Hexan-Luft-Gemisches durch Laserstrahlung

The ignition of an n-hexane-air mixture by a coherent light beam of a giant pulse laser was investigated by a statistical method. By analyzing the ignition probability and the development time from the ignition reaction to the formation of a measurable nucleus, which were calculated from the fluctuation of the ignition time-lags, the energy transferred from the light beam to the ignition reaction was estimated. The results suggest that the laser beam does not give energy directly to the developing process but only to the initiation of the ignition reaction. The development of the ignition reaction is accelerated during the breakdown process. That the quantitative effect on the ignition increases is due solely to the enlargement of the focal circle in the case of strong laser beam, while the actual energy supplied from the laser beam to the ignition reaction decreases. This means that there is an optimum energy of the laser beam for the ignition.

Investigation of non-linear absorption of light in solutions of cryptocyanine

Non-linear absorption of light in solutions of cryptocyanine in glycerol and methanol at light intensities between 2 × 10 5W/cm 2 and 5 × 10 9W/cm 2 was investigated theoretically and experimentally. Absorption cross sections and lifetimes of the excited states involved in the non-linear absorption process are estimated. Experimental evidence for the stationarity of the process in case of giant laser pulse excitation is given.

VARIABLY SPACED GIANT PULSES FROM MULTIPLE LASER CAVITIES IN A SINGLE LASING MEDIUM

Multiple laser cavities have been established in a single lasing medium. Single giant pulses with a time duration of 40 nsec have been emitted from each cavity and spaced less than 80 nsec to 4 μsec apart. The 0.4-mm spatial separation between the cavities indicates that many cavities could be established in a single lasing medium. Sequentially switching large numbers of cavities, repumping depleted regions, and reswitching could result in a high-repetition-rate giant-pulse laser system for use in photography and holography.

Motion and Collision of Plasma Blobs Produced by Giant Pulse Laser in a Transverse Magnetic Field

The properties of plasma created by the 200 MW giant pulse ruby laser irradiation on the lithium plate were investigated. Measurements of the variation of the shape and size of the plasma blob with and without the existence of the uniform magnetic field, its density, temperature, pressure, velocity of the motion and the electric field due to the charge separation were made. The phenomena occurring at the head-on collision of two blobs across the uniform magnetic field were also investigated and confirmed that the electric field could be canceled out at the colliding region.

Infrared Lasers Resulting from Giant Pulse Laser Excitation of Alkali Metal Molecules

Infrared laser action is observed to occur in vapors of K, Rb, and Cs photoexcited by various giant pulse laser beams. The mechanism of excitation involves two-photon absorption by the molecular species followed by dissociation into various excited atomic states. In the case of cesium, anomalously long infrared laser pulses are obtained when helium buffer gas is present. A collisional mechanism is invoked to explain this phenomenon. Self-focusing of a ruby laser beam is also observed to occur in cesium–helium vapor under certain conditions.

Nonlinear photoelectric electron emission induced by picosecond mode-locked laser pulses

The emission of photoelectrons from metals and semiconductors irradiated with relatively long light pulses from free-running or giant-pulse lasers has been already studied by a number of authors (1.~). I t seemed of interest to investigate the effects produced by irradiation with modelocked laser pulses of picosecond duration and power density of the GW/em ~ order. The pulses of this type were expeoted to permit the following observations.

Spatial coherence of the radiation emitted by a Q-switched ruby laser

The conditions for spatial coherence or noncoherence of a giant laser pulse are considered bearing in mind how the oscillation modes are affected by inhomogeneities in the permittivity or by changes in the permittivity due to the burning of holes in the population inversion. These conditions depend on the initial transverse distribution of the population inversion in the active rod and on the variation in the Q factor during the emission of laser radiation. The conditions were checked experimentally for a laser with a saturable filter excited under soft conditions.

Damage to transparent polymers caused by laser pulses lasting 10?3 and 10?8 sec

A study has been made of the internal damage produced in transparent polymers by laser pulses lasting 10−3 sec (free-generation mode) and 10−8 sec (giant-pulse mode). It has been established that in these cases different mechanisms are responsible for the damage. The action of giant laser pulses on transparent polymers evidently provides the first and so far only means of studying fracture effects associated with the truly instantaneous application of load, i. e., when the load application time is much less than the fracture time.

Heating of Laser Produced Plasmas Generated at Plane Solid Targets I. Theory

Abstract A hydrodynamic model for the heating of a plasma generated by the interaction of an intense giant laser pulse with a plane, solid target is developed. It is shown that in the case of nanosecond light pulses and a finite focal spot diameter, the plasma production may be considered as a steady state problem. Expressions for the electron temperature, the expansion energy of the ions, and the total particle number in the plasma as a function of the incoming light intensity are derived. An estimate of the ion temperature is discussed.

Stimulated Raman scattering excited by light of 5300Å

Giant pulse laser radiation at 530 nm excites strong stimulated Raman scattering in benzene at intensities above 140 MW/cm 2. Under special conditions (partially modulated laser radiation, parallel contracted beam, 20 cm long liquid cell) self-focussing, backward scattering and line broadening can be avoided. The threshold value found in our experiments is in accordance with the values found in ruby laser experiments, if the theoretical frequency dependence of the Raman gain is considered.

Higher order coherence effects of laser light on the photoelectron distribution detected by third order photoeffect

On decreasing the coherence volume of the giant pulse laser beam the statistical distribution of the photoelectron signal peaks due to third order photoeffect (TPE) was observed to undergo a marked change, while that for the linear photoeffect (LPE) remained unchanged

Acousto-optic method of producing giant laser pulses: Editorial Engineers Digest, Vol 30, No 8 (August 1969) p37 (2325)

Acousto-optic method of producing giant laser pulses: Editorial Engineers Digest, Vol 30, No 8 (August 1969) p37 (2325)

Fluorescence spectra and excited singlet-singlet absorption spectra of s-tetracyanobenzene EDA complexes by laser excitation

The excited singlet-singlet absorption spectra of s-tetracyanobenzene (TCNB) complexes with toluene and benzene were observed. The spectra were obtained using the re-absorption of the CT fluorescence by the fluorescent EDA complexes produced densely by means of the excitation with a giant pulse laser. The non-exponential decay characteristics, at the wavelengths of re-absorption, agreed quite well with theoretical expectations.

Chemical kinetics at the micro level: A laser micro temperature jump apparatus for relaxation studies in micro samples

The kinetics of chemical reactions at equilibrium can be investigated in samples of very small size with a giant laser pulse shifting the state of equilibrium by a temperature jump. The output of a Q-switched neodymium laser is fired into a microcavity of 5 μl. The solvent, which absorbs part of the laser energy, is heated instantaneously and the kinetics of the chemical processes leading to the new state of equilibrium can be followed up. The principles of the present design are based on the particular properties of a giant laser pulse—high energy and short duration, small beam divergence, emission at wavelengths where many solvents already absorb—and permits thereby (a) a very high time resolution, (b) a very small sample size (⩾ 5 μl), and (c) the use of polar as well as apolar solvents, since heating occurs by means of electromagnetic energy absorption instead of Joule-heating due to ionic conduction. The design of the instrument is such that reaction kinetics even in such integrated biological structures as single cells or cell organelles can be studied.