Electron-driven processes in high-pressure plasmas

This review article summarizes results from selected recent studies of collisional and radiative processes initiated and driven by low-energy electron interactions with atoms and molecules in high-pressure plasmas. A special emphasis of the article is on spectroscopic studies of plasmas used as sources for non-coherent vacuum ultraviolet radiation such as rare excimer emissions and atomic and molecular emissions from plasmas in admixtures of rare gases and the molecular gases H₂ and N₂. An attempt is made to correlate the various observed emission features and their dependence on the plasma operating parameters (pressure, power, gas mixture, mode of excitation, etc.) to the underlying microscopic atomic and molecular processes.     

High-power high-pressure pulsed CO2 lasers

The results of investigations and development of high-pressureCO ₂ lasers are considered. It is shown that the high-pressure active medium allows radiation pulses to be formed with smooth tuning of frequency and duration over wide ranges. Data on small-size wide-apertureCO ₂ lasers with an output pulse energy up to 5 kJ are presented. Institute of High-Current Electronics of the Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 74–77, August, 1999.     

Theoretical modeling of microwave-pumped high-pressure gas lasers

The electron avalanche and laser excitation processes in high-pressure discharges at microwave frequencies are investigated. In our model, the applied electromagnetic field is treated classically and assumed to be monochromatic. The Boltzmann equation for the electron velocity distribution function under the influence of an alternating electric field is numerically solved for a typical XeCl laser gas mixture. All relevant elastic, inelastic and electron-electron collisions are included in solving the Boltzmann equation. The theoretical modeling of microwwave-pumped high-pressure gas lasers are developed based on the first law of thermodynamics in order to determineE _rms/n (root-mean-square field strength/total number density of gas molecules) which is required by the Boltzmann equation to calculate the electron kinetics rates and microwave-power absorption by the plasma. A sample calculation of the microwave-pumped XeCl laser is presented, and a fair agreement between theory and experiment is seen.Paper partially presented at the 10th Int. Conf. on Lasers and Applications, Lake Tahoe, Nevada, USA (1987)     

Relaxational processes and instability in lasers

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 2, pp. 219–224, February, 1988.     

Noise processes in large ring lasers

Large ring lasers with a cavity Q well above 10¹² are characterized by extremely narrow line-widths and high coherence. At this point, active Sagnac interferometers do not quite reach the quantum limit. In this paper, we will explore the current status of this technology and look at the various noise processes involved with large ring lasers rigidly mounted to the Earth crust.     

Numerical modeling of active media of high-pressure group-II-metal lasers

Translated from a preprint (manucript) of the Lebedev Physics Institute, Russian Academy of Sciences, Moscow.     

Modeling of high-pressure 12-μm NH3 lasers

Experimental measurements of small-signal gain in an optically-pumped NH₃ amplifier are carried out at pressures ranging from 40 Torr to 760 Torr, and the results are used to validate a rate-equation model describing the amplifier dynamics. The gain measurements show that dilute mixtures of <0.5% NH₃ in N₂ are reqired to minimize the problems of gas heating due to pump absorption. The model is used to extrapolate the results to gas pressures of several atmospheres, and to demonstrate the potential for highpressure operation of optically-pumped NH₃ lasers. For a pump intensity of 100 MW/cm², calculations indicate that operation of an NH₃–N₂ laser is feasible up to a pressure of 10 atm, which would provide a maximum continuous tuning range of 4 cm^–1. High-resolution spectroscopy reveals that gain on a few NH₃ transitions is eliminated at high pressures due to the presence of overlapping absorptions in other NH₃ bands.     

Study of streamer development in high-pressure electric discharge: Applications to excimer lasers

This work represents a study of the streamer formation in plasma for XeCl excimer laser at high pressure. It is based on a longitudinal mono-dimensional model of the cathodic zone. In this model, we show the possibility of the streamer development in the cathodic sheath and its propagation during the phase of plasma formation. The model gives the space and time evolution of the electron density and the discharge electric field in the presence of the streamer. The obtained results clearly indicate that, for conditions close to experiments for 50–100 ns laser pulse durations and electron power deposition in the MW/cm³ range in a 300 cm³ chamber, the streamer instability, related to the sheath evolution, patently appears. The drift velocity reaches a typical value of about 10⁸ cm/s.     

Resonant second-order nonlinear optical processes in quantum cascade lasers

We demonstrate an efficient intracavity nonlinear interaction of laser modes in a specially adapted quantum cascade laser. A two-wavelength quantum cascade laser structure emitting at wavelengths of 7.1 and 9.5 micrometer included cascaded resonant optical intersubband transitions in an intracavity configuration leading to resonantly enhanced sum-frequency and second-harmonic generation at wavelengths of 4.1, 3.6, and 4.7 micrometer respectively. Laser peak optical powers of 60 and 80 mW resulted in 30 nW of sum-frequency signal and 10-15 nW of second-harmonic signal, both in good agreement with theoretical calculations.     

Pulsed high-pressure mercury capillary lamps: A new way of pumping dye lasers

A high pressure Hg capillary lamp (PEK AH 6-2-B) has been successfully pulsed to produce laser action in a methanol solution of Rhodamine 6 G. This lamp may provide a better laser efficiency than that available with a xenon flashtube.     

Dye lasers and intermolecular and intramolecular energy transfer processes

Computer calculations of ETDL performance indicate that dye laser output can be manipulated by an appropriate choice of a donor (absorber)-acceptor (dye) couple. Studies of relevant laser induced inter- and intramolecular energy transfer processes are presented. Presented in part at the European Physical Society Conference on “Physics and Chemistry of Laser-Induced Processes in Molecules”, Edinburgh (1978) [28].     

碰撞锁模环形染料激光器动力学过程的研究

本文在建立碰撞锁模(CPM)激光器数学模型的基础上,对碰撞锁模激光器中激光锁模脉冲形成的动力学过程进行了计算机模拟计算,并对其结果进行了理论分析和讨论,得到了脉冲宽度、脉冲波形及对称性与泵浦速率、腔长、增益介质和可饱和吸收介质在腔内的相对位置等因素间的关系。     

On cutting and penetration welding processes with high power lasers

In this paper cutting and continuous welding laser processes are examined. Experiments with CO₂ and YAG lasers were carried out on carbon and stainless steels. Two distinct regimes were identified in the gas jet assisted cutting process and in both cases predictions of working parameters can be made. Penetration welding results, when represented on a mathematical model, were seen to be similar to those of cutting ones. Finally, there is a great difference between the above processes and the conduction welding one.