Evgeny L. Latush

Mathematical modeling of ion recombination strontium vapor laser

In the present work, a self-consistent model of the He-Sr recombination laser is developed. With this model one can calculate plasma parameters and laser characteristics in pulsed-periodic regime and also carry out multiparametric optimization of the laser. The calculations carried out by the model show that under a wide range of conditions (pHe=3 Torr-3000 Torr) the model allows to trace rather precisely all trends in the behavior of plasma parameters and laser characteristics. The calculations of laser characteristics carried out for 7 active elements with different geometry (la=9-70 cm, d =0.3-1.55 cm) show good agreement with experiment. The developed model can serve as a convenient tool for investigating kinetics of the active medium of the He-Sr laser.

Strontium and cadmium pulsed cataphoretic lasers

For the first time, the cataphoretic input of metal vapor into active media of the pulsed He-Cd+ and He- Sr+ lasers is proposed and experimentally realized. For small-size cataphoretic recombination He-Sr+ laser with discharge channel of 3 mm i.d. and active length of 26 cm, rather high values of the average output power (510 mW) and record values of specific average output power (277 mW/cm3) as well as gain coefficient (0.15 cm-1) were achieved.

He - Sr Recombination laser with helium pressure up to 5 ATM

The He-Sr recombination laser is an effective source of coherent radiation in the violet (430.5 nm). A self-heating longitudinal laser with an active-medium volume [approximately] 100 cm[sup 3] and a helium pressure [approximately] 500 torr usually delivers an average lasing power at a [approximately] 1-W level, an efficiency [approximately] 0.1%, and a pulse repetition frequency 4-6 kHz. With forced water cooling of the active part of the discharge the power reached 3.9 W from a tube 1.1 cm in diameter and 33 cm long, by raising the pulse repetition frequency to 29 kHz. The need for high buffer-gas pressures is determined by the recombination mechanism of the laser-transition pumping: elastic collisions of the electrons with the helium and atoms and ions in the afterglow of the discharge cool the electron gas, contributing to an ever more effective recombination process and consequently to a rise of the pump level. The present paper attempts to determine the helium pressure at which the output power and the lasing-pulse energy of an He-Sr laser begin to sag.

Studies of the Longitudinal Electrophoresis Dynamics in Pulse-Periodic Discharges

The establishing in time of the axial distribution of metal vapors is studied on injecting them electrophoretically into a pulse-periodic discharge. In particular, the time-dependent solution of the diffusion equation for the metal vapor concentration is obtained averaged through a number of pulses. The axial distributions of vapors for various instants of time are calculated. The homogeneity criteria for these distributions are determined. The settling times of the homogeneous distribution in conditions typical for the pulse-periodic metal vapor lasers are found. These times are rather short (about 1 s). The results obtained show promise for using electrophoresis in pulse-periodic metal vapor lasers to form homogeneous active media.

Deionization of afterglow plasma of pulsed lasers through intensified ambipolar diffusion

Method of electron concentration (ne) reducing in an interpulse period is proposed, based on ambipolar diffusion (AD) rate increase to the tube walls. As the AD coefficient Da equals D(1-Te/T), the heating of electrons by weak electric field to the Te <EQ 1 (epsilon) B, yet insufficient for ionization although much higher than the gas temperature T, considerably hastens the process of ion removal to the walls. Effect of the intensified ambipolar diffusion (IAD) was registered experimentally by us in the afterglow of zinc and cadmium metal vapor ion lasers. In this work, computer modeling of the IAD is performed for He- Cu and Ne-Cu discharge afterglows with parameters typical for self-terminated copper vapor laser. As the calculations demonstrate, at helium pressure of about 10 Torr and tube diameter approximately 1 cm, when heating field E of 0.8 - 0.9 V/cm is imposed on afterglow for a time period of 100 microsecond(s) , ne slides down to values of 102 - 104 times smaller as compared to those without heating. The effect is stronger in helium. The use of IAD in interpulse period would allow, as calculations reveal, up to 20 - 40% increase of pulse repetition rate in the copper vapor laser with small tube diameters and low buffer gas pressures. The excess build up of copper metastables density is prevented by interruption of plasma heating 3 - 5 microsecond(s) prior the onset of a main current pulse.

New stepped spherical x-ray diffractor for microprobe analysis

X-ray microprobe techniques require both a good spectral resolution and a high intensity. Actually, these two competitive conditions can be obtained only by x-ray spectrometers with focusing optics made by cylindrical curved crystals or by doubly curved on spherical or toroidal surface crystal monochromators. However, these devices do not allow collection of a large solid angle and therefore the experiments are limited by the source brilliance. Here we present a special device for the analysis of the x-ray secondary emission based on a new diffractor design. The device has a special shape of the reflecting surface, i.e., a pseudo- spherical stepped surface characterized by a constant angle width per step, that allows to collect the large solid angel necessary to guarantee an intense flux for the experiments of microanalysis. We will demonstrate that the efficiency of this diffractor is superior to a commercial device of similar size having a spectral resolution of 410-4 with a potential gain of about one order of magnitude.

Strontium and calcium vapor recombination lasers: excitation mechanisms, operation regimes, and applications

A review of the latest studies on the Sr-He and Ca-He gas-discharge lasers emitting in blue- violet and UV spectral regions is presented. On the basis of plasma diagnostics and spectroscopic investigations, the conclusion is drawn on the recombination excitation mechanism prevalence. Laser tubes of various designs with longitudinal and transverse discharge excitation, their operation regimes and output characteristics, are analyzed, including a regime of simultaneous oscillations on recombination, charge-transfer pumped, and self-terminating electron-impact excited laser transitions. Already realized and perspective applications of the lasers are also discussed.

On the possibility of lasing on new transitions of Sr II under conditions of strongly nonstationary recombination kinetics

A search for new laser transitions is carried out in the spectrum of Sr II by using a mathematical model of the He-Sr recombination laser. The calculations revealed that under strongly non-stationary conditions it is possible to obtain a population inversion and lasing at the leading edge of the recombination pumping pulse on the ultra-violet transitions 52D3/2,5/2→52P1/2,3/2Sr II (λ = 338.1 and 346.4 nm). In this regime, the inversion arises as a result of transient processes at the establishing of populations of laser levels and it exists several nanoseconds, similar to that of self-terminated lasers.

Dynamics of cataphoresis in the pulse-periodic discharge

The processes of temporal evolution of metal vapor longitudinal distribution in the pulse-periodic discharge with the cataphoresis delivery of vapor are investigated. In particular, the solution of a non-stationary diffusion equation for the density of metal vapor, averaged for rather large number of pulses, is derived. The axial distributions of metal vapor at different moments of time are calculated. The criteria of uniformity of these distributions are determined. Time intervals are found for homogeneous distribution establishment in typical pulse-periodic MVLs conditions. These time intervals showed to be fairly small, on the order of second. The obtained results demonstrate good perspectives for the use of cataphoresis in pulse- period MVLs to form the homogeneous active mediums and, as a consequence, obtain high output characteristics of lasers.

Optimal scaling of He - Sr{sup +}(Ca{sup +}) recombination lasers

A method for scaling optimal parameters of the discharge-heated He - Sr{sup +}(Ca{sup +}) recombination lasers is suggested. The method can be used for calculating the optimal excitation parameters and output characteristics of laser tubes of arbitrary dimensions from the known parameters of the optimised laser tube. The experimental verification of the scaling relations showed reasonable agreement between calculations and the experimental data, which is acceptable for practical applications. (lasers)