Laser-induced gas-surface interactions

Quantum theory of solitons

Chiral Gauge Theory

Theabilityofanelectrohydrodynamicactuatortomodifythecharacteristicsofa e owovera e atplateisanalyzed. Thedeviceconsidered usese ush-mounted electrodes and a dcpowersupply to createa plasma sheeton thesurface of the plate. We analyze the mechanism of formation of this plasma sheet, which has some similarities with the phenomenon of streamer formation. Experimental results are presented concerning e ow visualizations obtained at low e ow velocities (o 1 m/s) and velocity e elds obtained with a particle image velocimetry technique for higher e ow velocities (range 11.0-17.5 m/s). These results show that the discharge can induce an important acceleration of the e ow close to the surface. ORONAS are self-sustaining discharges characterized by a strong inhomogeneity of the electric e eld cone guration and electrodes having a low curvature radius. This cone guration cone nes the ionization process to regions close to the high-e eld electrodes. Thus, in this phenomenon, there are active electrodes, surrounded by ionization regions where free charges are created, a low-e eld drift region where charged particles drift and react, and low-e eld passive electrodes. Coronas can be unipolar or bipolar if oneorbothelectrodesareactiveelectrodes.Bipolarcoronascanlead to the formation of streamers, weakly conducting plasma e laments extending from one electrode and carrying their own ionization re- gion ahead of themselves. Positive streamers are cathode directed and negative streamers anode directed. The physics of corona discharge occurring in a gas close to an insulating surfacehasnotbeen as widely studied as coronaswithout anyextraneousbodiesinthevicinityofthedischarge. 1;2 Becausethe discharge involves the movement of ions as well as a large amount of neutral particles, this situation becomes of special interest in aerodynamics for e ow and instabilities control. The induced e uid motion is usually called electroconvection or sometimeselectricwind.Coulombianelectroconvectiontakesplace ifthecoulombianforcesactingonthee uidparticlesarepredominant in relation to the polarization ones. This is usually the case when the e uid medium is air. The way the electric forces act on e uid particles may be explained by considering that ions in their drift motion from one electrode to the other will exchange momentum with the neutral e uid particles and induce their movement. Because currents involved in the process are so lowthat magnetic effects can be disregarded the phenomenon is described by the set of equations used in electrohydrodynamics (EHD) problems.

Flow Control with Electrohydrodynamic Actuators

Various forms of CO 2 lasers have achieved CW powers in the 60-kW range, operating efficiencies approaching 30 percent, pulse energies of approximately 2000 J, pulsewidths less than 1 ns, peak pulse powers in excess of 109W, a frequency stability of a few parts in 1012, and sealed-off tube lifetimes of many thousands of hours. In addition, the laser can be easily Q-switched as well as gain-switched and has been electrically, optically, gas-dynamically, and chemically pumped. In addition to all these attributes, the CO 2 laser output wavelength lies within one of the best atmospheric windows. It should be no surprise then that during the last eight years, the CO 2 laser has firmly established itself as a candidate for recognition as the most important among the numerous laser devices presently known. Depending on the gas pressure, gas flow rate, pumping mechanisms, gas mixture, etc., CO 2 lasers can exhibit a wide range of noise, bandwidth, gain, and power saturation characteristics. This flexibility enables a designer to optimize the performance of CO 2 laser stable-frequency master oscillators; power oscillators; low-noise high-gain preamplifiers; intermediate-power or high-power amplifiers. As a result, CO 2 laser oscillator-amplifier chains can be designed utilizing guidelines similar to those which have been extensively applied in the design of transmitters in the RF and microwave region of the electromagnetic spectrum.

Review of CW high-power CO 2 lasers

The results are reported of an experimental investigation of the possibility of using a surface discharge plasma as a cathode in a pulse CO2 laser A self-sustaining cavity discharge and laser action were achieved in a volume of 08 liter at a pressure up to 15 atm in the laser mixture The specific energy output reached 20 J?liter?1?atm?1 when the specific energy input was 165 J?liter?1?atm?1 and the input efficiency was 12%

Plasma-sheet CO2 laser

A theoretical analysis is made of the thermal action of high-power laser radiation on the surface of a solid. Temperature and stress fields generated in an irradiated solid are investigated. Dependences of the maximum laser radiation intensities are calculated as a function of the pulse duration. These calculations are made for three states of a reflecting surface corresponding to maximum permissible elastic stress on the surface, plastic flow producing residual stresses, and melting of the surface layer.

Nikolai V Karlov

Papers

Plasma-sheet CO2 laser

Thermal action of high-power laser radiation on the surface of a solid

Excitation of an Explosion Wave by Initiating a Chain Reaction in a Gas Mixture with CO 2 -Laser Radiation

Selective heterogeneous separation of vibrationally excited molecules

Self-focusing of CO 2 Laser Radiation in Resonantly Absorbing Gases