Discharge CO Laser Research Articles

Adding Effect of Xylene in TEA Double Discharge CO2 Laser

Adding Effect of Xylene in TEA Double Discharge CO2 Laser

Laser power and vibrational energy transfer in CO2 lasers

The decay of the laser power in the afterglow of a CO2 laser discharge is shown to be exponential when the upper laser level is excited directly by electrons. The decay time is shown to be a function of the rate coefficients describing the relaxation of the lower laser level. From power decay measurements it is found that the deactivation of the lower laser level to the ground state occurs in two steps. The rate coefficient for the transfer of vibrational energy from the 1000 level to the 0110 level of CO2 is found to be 5× 10−13 cm3 sec−1. This is an order of magnitude smaller than a previously reported value. The rate coefficients for the relaxation of the 0110 level of CO2 by H2O and D2O are found to differ by a factor of 1.8. These rate coefficients increase with increasing temperature in agreement with calculated results using the theory of Marriott. The measured dependence of the relaxation time of the lower laser level on the H2O vapor density explains the observed maxima of the laser power and small signal gain in conventional and gas-dynamic CO2 lasers. The power decay for a CO2 laser, when the upper laser level is additionally excited indirectly via the N2 (ν = 1) level, is shown to be described by the sum of two exponential functions. The two time constants depend on the rate coefficients for the relaxation of the lower laser level as well as for the transfer of energy from the N2 (ν = 1) level to the upper laser level. The decay time of the laser power is found to increase with increasing N2 density.

Ionization instability in CO2 laser discharges

Criteria are established for calculation of plasma conditions leading to ionization instability in plasmas generally employed in high-power molecular laser applications. Negative ion formation is found to play an important role in causing this instability. For conditions typical of electrically excited CO2 laser mixtures, appearance of an ionization instability requires a negative ion concentration greater than one-tenth that of the electrons, combined with an electron temperature value below approximately 1.5 eV. Satisfactory agreement between theoretically determined stability boundaries and data obtained experimentally confirms the significance of fundamental collisional processes as regards ionization instability in CO2 laser discharges.

Vibration-vibration energy transfer in CO2 glow discharges

Short-duration 10.6-μm pulses are used to perturb low-pressure CO2 laser discharges. Various spontaneous emissions from the glow discharge are monitored as they return to their steady-state values. Vibration-vibration (VV) pumping between CO2(ν3) and CO (produced by dissociation or premixed) as well as N2 has been observed in three independent studies. Data obtained from these studies correlate well with each other. When the reciprocal time constant for the VV process is plotted against pressure, a straight line is obtained as predicted by theory. The slope of this line is consistent with rate-constant data taken from laser-induced fluorescence experiments.

Physics of CO, Electric Discharge Lasers

Detailed analytical and experimental investigations of the major factors which influence the performance of CO2 electric discharge lasers have been conducted. Rates of electronic excitation of key laser levels have been computed from analytically determined electron energy distributions which are non-Maxwellian in CO2 laser discharges. Combination of these data with a model of molecular kinetic processes has permitted quantitative calculation of important laser properties such as gain and saturation intensity as a function of various discharge parameters. Further, analysis of discharge plasma properties has made possible comparison of calculated results with experimental data yielding both qualitative and quantitative agreement. These results reveal the dependence of laser properties on discharge characteristics, thereby illuminating the central features of CO2 laser operation.

Numerical Modelling of Pulsed Electric CO2 Lasers

A simple four-level kinetics model is combined with a cavity intensity model to predict the output pulse characteristics of pulsed electric discharge CO2 lasers for pressures ranging from 0.1 to 10 atm. Both free-running (gain-switched) and Q-switched cases are studied. Particular emphasis is placed on peak intensity and energy content of the initial spike as a function of pumping rate, gain at time of Q swithcing, mixture, and pressure.

Parametric Behavior of the Atmospheric Pressure Pulsed CO2 Laser

Megawatt peak powers have recently been reported from a pulsed electrical discharge CO2 laser operating at atmospheric pressure [A. J. Beaulieu, Laser Focus 6, 14 (1970)]. The electrical discharge was struck across the transverse dimension of the laser producing the large electric field strengths required for laser excitation at high gas pressures. This paper describes the small signal gain, pulse energy, and duration as a function of gas pressure and discharge voltage of a 1.5-m laser tube utilizing 60 separate capacitor discharges along the axis of the tube. The gain coefficient is of the order of 1% per cm or less, typical of dc excited CO2 lasers. The peak power increases approximately as the square of the total gas pressure as a result of an increase in pulse energy and decrease in pulse duration with gas pressure.

MAGNETICALLY STABILIZED CROSS-FIELD CO2 LASER

A new concept of stabilizing an electrical CO2 laser discharge against a transverse gas flow is described. A cross magnetic field, mutually perpendicular to the discharge axial electric field and the gas flow velocity, is employed to maintain the electrical discharge column colinear with the optic axis. The cross-field laser is convectively cooled and characterized by low flow velocities, low pressure drops, and high operating efficiencies.

CARBON MONOXIDE FORMATION IN CO2 LASERS

The rate of CO2 dissociation in a flowing CO2 laser discharge has been measured. This rate is consistent with published cross sections for direct electron impact dissociation when averaged over the appropriate electron energy distribution. The dissociation process in the flowing gas discharge is found to result in an axial variation of plasma properties and of the laser medium. Implications of the CO variation for many conventionally operated CO2 lasers are discussed.