Electric-discharge CO2 Laser Research Articles

Cryogenically cooled CW electric discharge CO laser operated with CO2 laser mixture

We report lasing on multiple wavelengths in the 5 µm region from a non-selective CW-CO laser cavity utilizing the CO2 laser gas mixture when its gain length was maintained at LN2 temperature. The inversion obtained in the CO medium formed by the dissociation of CO2 gas in the discharge made this possible. The findings are significant as the handling of the toxic CO gas that is conventionally employed in the generation of wavelength in the 5 µm region has been dispensed with. A maximum CW output power of 8 W was obtained at an electro-optic efficiency of 8%. The cascading lasing transitions have been identified and matched with known transitions available in the literature.

On the Thermal Spectra of Ruby and Sapphire

The temperature dependence of the thermal spectra (in the range from 0.4 to 8 μm) of ruby and sapphire single crystals heated by a 10.6-μm cw electric-discharge CO2 laser has been experimentally and analytically investigated. The shape of the background of the spectral lines of impurity Cr3+ ions in ruby corresponds to the short-wavelength tail of sapphire thermal radiation. The Planck thermal spectrum of sapphire is interpreted in terms of the interaction between electrons and lattice ions in the conduction band.

Theoretical investigation of the regenerative amplification of ultrashort pulses in a high-pressure transverse electric CO2 laser.

We have developed a theoretical model for the regenerative amplification of ultrashort mid-infrared radiation in high-pressure transverse electric discharge CO2 lasers. This model is based on counter-propagating wave equations that are combined with Boltzmann equation, six-temperature, and circuit-coupled kinetic models. For the first time to our knowledge, the effect of spontaneous emission is taken into account. The model describes noise behavior, contrast ratio, and self-lasing of amplified spontaneous emission. The proposed scheme allows the attainment of a few-picosecond pulse with GW-level peak power and contrast ratio on the order of 106 in the 9μm range.

Influence of nitrogen on CO-laser characteristics

The role of the addition of nitrogen to the discharge plasma of CO lasers on plasma-chemical processes is discussed here. It is shown that nitrogen addition improves laser characteristics and changes the composition of the laser active medium. A reduction of CO highly-excited vibrational-states populations with current is smaller in the case of mixtures with nitrogen additions. The addition of nitrogen significantly decreases CO dissociation level and concentrations of C atoms created in plasma-chemical reactions of laser discharge. Full Text: PDF ReferencesG.M. Grigorian and I.V. Kochetov, "Balance of CO molecules in the plasma of a sealed-off CO laser", Plasma Phys. Rep. 30, 788 (2004). CrossRef V.S. Aleinikov and V.I. Masychev, CO Lasers (Moscow, Radio i Svyaz' 1990).A. Cenian, A. Chernukho, V. Borodin and G.Śliwiński, "Modeling of Plasma-Chemical Reactions in Gas Mixture of CO2 Lasers I. Gas Decomposition in Pure CO2 Glow Discharge", Contr. Plasma Phys. 34, 25 (1994). CrossRef A. Cenian, A. Chernukho, V. Borodin, "Modeling of Plasma-Chemical Reactions in Gas Mixture of CO2 lasers. II. Theoretical Model and its Verification", Contrib. Plasma Phys. 35, 273 (1995). CrossRef A. Cenian, A. Chernukho, P. Kukiełło, R. Zaremba, V. Borodin and G. Śliwiński, "Improvement of self-regeneration of gas mixtures in a convection-cooled 1.2 kW laser", J.Phys. D: Appl.Phys. 30, 1103 (1997). CrossRef E.A. Trubacheev, Trudy FIAN 102, 3 (1977).G.M. Grigorian, B.M. Dymshits and Yu.Z. Ionikh, "Influence of oxygen on the parameters of the active medium in an electric-discharge CO laser", Sov J Quant Electron 19, 889 (1989). CrossRef V.N. Ochkin, S.Yu. Savinov, N.N. Sobolev and E.A. Trubacheev, Kvant. Elektr. 1, 573 (1974).

Amplification of a train of nanosecond pulses from a frequency-selective CO laser by an electric discharge CO laser amplifier

The output characteristics of an electric discharge CO laser amplifier with an input in the form of a nanosecond (ns) pulse train of wavelength-selective CO laser emission (λ = 5.28 μm) were calculated. The input pulse train characteristics were assigned on the basis of experimental data. The calculated multiplication factor of the first 200 pulses in the laser amplifier is in good agreement with the experimental data. It is shown theoretically that at conditions under study, both the individual pulse shapes and multiplication factor of a train composed of 200 pulses are sensitive to magnitudes of rotational relaxation rates for populations of involved rotational–vibrational energy levels of a CO molecule. It is shown theoretically that the output characteristics of the laser amplifier are not sensitive to the variation of the radial profile of the axisymmetric input laser beam. It is predicted that experimental study on amplification of a separate short pulse will allow evaluation of the rotational relaxation rate with better accuracy.

Dynamics of the Working Medium of a Diffusion-Cooled Electric-Discharge CO2 Laser with Periodic Heat Release in the Axial Region of its Cylindrical Resonator

The dynamics of the gas mixture in the cylindrical resonator of a CO2 laser with periodic heat release in the region of its axis was defined on the basis of the numerical solution of the system of Navier–Stokes equations by the explicit MacCormack method with splitting of the initial operator in space directions. The space fields of the gas-dynamic functions of the gas mixture and the ranges of their change were determined, and the character of the averaged flow of this mixture was investigated.

Flow fluctuation measurement in the flow-through path of continuous electric-discharge CO2-laser contour

We have experimentally proved the applicability of hot-wire anemometer method to measure fluctuations at low pressures and gas flow rates when medium is no longer considered as continuous. Use of individual calibration at working conditions serves to apply standard technique for determination of sensitivity coefficients of hot-wire probes. Additional investigations are necessary to take into account influence of Knudsen number and, possibly, other parameters in heat transfer law presented as criterial dependence of Nusselt number on Reynolds number. Hot-wire measurement of mean velocity distribution and their fluctuations in the flow-through path of electric-discharge CO2 laser have been performed. The level of velocity fluctuations in the vicinity of anode is high that is caused by the zone of interacting flows from the ventilators rotating in opposite directions forming in the symmetry plane. Placing of the damping screen between the ventilator and air gap allows decreasing fluctuations intensity to the acceptable level. It has been ascertained that the vortex shedding with high intensity of fluctuations which influence is noticeable in significant part of air gap is formed in the wake behind the streamlined cathode. However, pulsation level in the proper gap does not exceed permissible values.

Spectra of the selective heat radiation of Yb2O3 under the laser thermal excitation

The dependence of the spectra of the near-IR and visible selective heat radiation (SHR) of the Yb2O3 polycrystals that are synthesized using the laser thermal method on the excitation intensity of the CW electric discharge CO2 laser at the wavelength λ = 10.6 μm is experimentally studied. The SHR spectra are determined by the multiphonon excitation of the vibronic states of the 2 F 5/2 term in the Yb3+ ions and the radiative transitions to the vibronic states of the ground term 2 F 7/2.The laser heating of the polycrystals to the melting point causes the anomalous growth of the SHR spectral peaks in the wavelength range λ ≥ 1040 nm due to an increase in the intensity related to an increase in the probabilities of the radiative vibronic transitions owing to the thermal increase in the phonon density. The effective conversion of the thermal energy of the Yb2O3 polycrystals into the SHR indicate the significant role of the radiative cooling of surface.

Electric-discharge high-peak-power CO2 laser

A new electric-discharge CO2 laser with a peak power of up to 45 MW and a half-height pulse duration of 50 ns is developed. The short laser pulse was formed using a generator with a semiconductor opening switch. The maximum laser radiation energy reached 6.2 J and the efficiency with respect to the stored energy was 15%. The first peak contained 70% of the energy, and the pulse duration at the base did not exceed 1 μs.

Numerical modelling of kinetic processes in the plasma of a supersonic electric-discharge CO laser excited by a microwave discharge

A model is developed for calculating pump parameters of the active medium of a supersonic electric-discharge CO laser excited by a microwave discharge. A variant of the design of such a radiation source is described. Calculations are performed both for the 'hot' variant of the radiation source, when the gas mixture is produced by burning the fuel in a gas generator, and the 'cold' variant, when the gas mixture is supplied to the discharge region from gas vessels. The regions of optimal values of the reduced field strength and parameters of the gas mixture for the 'cold' variant are determined. It is shown that the parameters of the active medium obtained in the 'hot' variant correspond to the parameters of highly efficient radiation sources reported in the literature.

Optimization of the CO2:N2:He Ratio in the Active Media of Continuous-Wave Electric-Discharge CO2Lasers

It is shown that the optimum ratio between the main components CO2:N2:He of the active medium of continuous-wave electric-discharge CO2 lasers depends on the temperature of the active medium. Continuous-wave CO2 lasers can operate effectively at high temperatures of their active medium (T ∼ 1000 K) if in their composition the fraction of N2 molecules is increased as compared to the fraction of CO2 molecules (CO2:N2 < 1:15) and the fraction of He atoms is decreased (He n< CO2 + N2).

High-quality beam generation in a 8-kW cw CO2 laser

The use of a self-filtering cavity in a laser makes it possible to obtain a high-quality high-power output beams. A maximum output power of 8.3 kW with an electrooptical efficiency of 11.3% is obtained. Estimates show that a high-quality beam with power up to 20 kW can be generated in electric-discharge CO2 lasers with a self-filtering cavity.

The effect of nanosecond ionization on the characteristics of a fast-flow CO2 laser with self-sustained discharge

We studied the possibility of increasing the electric discharge stability, efficiency, and working range of a technological continuous-wave electric-discharge CO2 laser at the expense of an additional pulsed ionization produced by nanosecond high-voltage pulses.

Light-Induced Cooling of the Active Medium of a Fast-Circulation CO 2 Laser in the Field of Generated Radiation

Using the methods of emission spectroscopy, we studied the influence of generated radiation on heating the active medium of a fast-flow electric-discharge CO2 laser.

The effect of temperature on the creation of population inversion in the active media of electric-discharge CO2 lasers

It is shown that population inversion can be created on the 0001–1000 transition in the active medium of an electric-discharge CO2 laser even if its temperature increases to ~1200 K. By retaining the discharge stability and increasing the selectivity of the upper level pumping, it is possible to build electric-discharge CO2 lasers without water cooling.

Mechanisms and relationships governing the propagation of pyrolysis and combustion waves along a laser beam

The relationships governing the propagation of pyrolysis and combustion waves along an electric-discharge CO2-laser beam in propane and propane — air mixtures were investigated. It was shown that, after the preliminary conversion of propane in the pyrolysis waves, the average velocity of the combustion wave along the laser beam increases by a factor of 6 — 7. It was established that the velocity of the combustion wave along the beam is proportional to the chain-branching rate constant and that the wave appears as a result of consecutive ignition of the mixture along the beam (analogous to an electric breakdown wave).

Limitation of the output power of cw electric-discharge CO2 lasers

The output power of a sealed-off tunable cw CO2 laser was optimised. The dependences of the small-signal gain for the 10P(20) line and of the output powers for different transmittances of the cavity on the discharge current were determined. The distributed loss coefficient and the saturation parameter were measured. The saturation parameter increased continuously with increase in the discharge current, leading to a mismatch between the output power and gain maxima. It was established that the principal factor limiting the output power of cw electric-discharge CO2 lasers is not an increase in the temperature of the active medium but the dissociation of CO2 molecules. When the latter is minimised in order to achieve the maximum laser power, low gas temperatures are not required.

Calculation of the vibrational temperatures and populations of the laser-active levels of CO2 from the spectral distribution of the gain

The gains measured at the centres of vibrational — rotational lines of the main bands of the CO2 molecule were used to determine, by the least-squares method, the populations of the laser-active levels and the vibrational temperatures of the active medium of a cw electric-discharge CO2 laser.

Efficient electric-discharge CO2 laser with a prepulse formed by a generator with an inductive energy storage device

Results are presented of experimental investigations of a CO2 laser pumped by a self-sustained discharge from a generator with an inductive energy storage device and a semiconductor current chopper. It is shown that the energy stored in the inductance of the discharge circuit can form a prepulse capable of depositing most of the energy in the active mixture for nearoptimum values of the parameter E/p. A radiation energy of 3 J was achieved in an electricdischarge laser with a 0.181 liter active volume with a 17% efficiency relative to the energy stored in the capacitive storage device.

Spectral and temporal characteristics of the radiation emitted by a fast-flow electric-discharge CO2 laser

Experimental and theoretical investigations were made of the spectral and temporal characteristics of the radiation emitted by a cw fast-flow electric-discharge CO2 laser. A discharge chamber, separate from the cavity, was filled with a nitrogen-helium mixture at pressures of 6.5–12 kPa. When the input energy was above 200 J g-1, simultaneous steady-state stimulated emission of the P(22), P(20), and P(18) lines was observed. At input energies up to 100 J g-1 the laser radiation had a broader spectrum.