M. F. Sem

Pulsed metal vapor ion lasers

The paper reports up to day progress in investigations and developments of ion metal vapor lasers, excited by three of the most effective processes in gas discharge plasma, namely, by collisions of metal atoms with electrons, by the collisional-radiative recombination of doubly-charged metal ions and by heavy-body collisions of the metal atoms with buffer gas ions or metastables. The main attention given to the latter type of excitation in the plasma of pulsed hollow cathode discharge and the output characteristics are presented and discussed. The output characteristics of the hollow cathode discharge ion laser with combine active media (He-Kr-Hg mixture) emitted on (lambda) 469,4 nm Kr+ and (lambda) 615 nm Hg+ lines are presented.

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.

OPTIMUM CONDITIONS FOR PUMPING LASER TRANSITIONS OF CADMIUM IONS BY VARIOUS PROCESSES IN A HOLLOW-CATHODE DISCHARGE

The interaction of electrons of various energies with helium and cadmium atoms in a hollow-cathode discharge is analyzed. On the basis of the results of this analysis the conclusion is made that helium is ionized predominantly by electrons moving from the cathode wall to the cavity axis and having energies 70<ε<300 eV, whereas helium and cadmium are ionized predominantly by electrons with energies 9<ε<70 eV which move chaotically. For each of these energy ranges, the kinetic equation is solved and the electron energy distribution function (EDF) is determined, which is used for calculating pumping rates for laser transitions of cadmium ions. The conclusion is made that the rate of population of laser transitions through charge transfer is determined by electrons having a predominant direction of motion and an anisotropic EDF. The population rate associated with electron impact and the Penning ionization is determined by electrons moving chaotically and having an isotropic EDF. The analysis of the EDF made it possible to explain differences in discharge conditions (helium and cadmium pressures) providing optimum lasing for lines pumped by different processes. Radial profiles of pump rates obtained from the analysis made it possible to calculate and explain the dependence of the laser output power on the cathode diameter.

Spectral and power output characteristics of the pulsed He-Hg+ and Ne-Tl+ hollow-cathode lasers with charge-transfer excitation

The plasma parameters and output power characteristics for pulsed ion He-Hg+, Ne- Tl+, Ne-Ga+, and He-Cu+ lasers in hollow cathode discharge are presented and discussed. The populations of the upper laser levels pumped by means of charge transfer between metal atoms and buffer gas ions and destroyed by electron de- excitation process are determined not only in the afterglow but also during the current pulsewidth. The measurements show that the pulsed laser lines of 615 nm Hg+ and 595 nm Tl+ are most effective, and average output powers on these lines up to 880 mW and 285 mW at pulse repetition rate of 40 kHz and 15 kHz, respectively, were obtained. The isotopic and hyperfine structure of Hg+ and Tl+ laser lines is revealed.

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.

Small-scale efficient He-Sr + (Ca + ) recombination lasers

Systematic overview is presented of the design and output parameters of the small scale (1 + (430.5 nm), He-Ca+ (373.7 nm) gas- discharge recombination lasers. Such compact lasers are usually characterized by reliability, durability, ease of handling; they demonstrate elevated pulse repetition frequencies f, better quality of laser radiation, and high specific output powers.

Output characteristics and excitation mechanism of multiline He-Cd+ hollow-cathode laser

The properties of cadmium ion level excitation by means of second-kind collisions with buffer gas ions or metastable atoms in a negative glow of steady-state hollow cathode discharge are discussed. The electron energy distribution function, electric field distribution, and relevant level excitation rates were calculated and measured. The laser output power was measured as a function of discharge parameters and laser tube design for blue (441.6 nm), green (533.7 and 537.8 nm), and red (636 nm) He-Cd+ laser lines in continuous wave hollow cathode discharge both in lasing at individual lines and in three-color output regime that gives white- light emission. Output powers of 115 mW, 25 mW, and 13 mW for blue, green, and red lines, respectively, and a noise level less than 1% rms were obtained.