Large aperture CO2laser discharges

Large aperture high-pressure gas laser discharges are a prerequisite for the development of high-energy gas lasers of sufficient power for the production of plasmas of thermonuclear interest. Of the several approaches being followed toward the attainment of such discharges, one utilizing weak volumetric preionization of the active gas region produced by UV radiation is described. The use of this technique has resulted in the successful generation of atmospheric-pressure CO2laser discharges between electrodes separated by 30 cm, having total cross sections of ∼600 cm². With input energies of ∼200 J/1 small signal gain values of 4-5 percent cm^-1were measured in 1 : 1 : 3 gas mixtures of CO2, N2, and He, respectively. It is thus concluded that this excitation technique could be incorporated into the fabrication of large volume gas laser amplifiers having beam cross sections in excess of 10³cm²and total output-energy capabilities ofsim 10^{4}J.     

Behavior of first- and second-positive emission in the N2/SF6laser

Experimental results for the behavior of the emission of the discharge-excited first- and second-positive bands of N2and flow-tube measurements for the deactivation of theA^{3}Sigmamin{u}max{+}andB^{3}Pi_{g}levels of N2by SF6are presented. The results of both these experiments are used to explain the operating mechanisms of the N2/SF6laser.     

Radial gain profiles in CO2laser discharges

Measurements of the gain of the P(20), 10.6 μ, transition of CO2have been made in a flowing He, N2, CO2amplifier. Both small-signal and saturated gain conditions were investigated as a function of radial position. At low discharge currents, the radial small-signal gain profile followed a J0Bessel function distribution as predicted from the electron density distribution, while at higher currents, the gain was nearly constant across the tube diameter. Further increases in the current produced a lower gain on the tube axis than near the tube wall. This spatial behavior of the small-signal gain with discharge current can be understood following the theoretical models of Gordietz et al. or more recently of Wiegand et al. The theory indicates the small-signal gain behavior is largely explained by the increase of axial gas temperature with discharge current. Gain measurements at signal levels high enough to cause gain saturation indicate the gain is harder to saturate on the tube axis than near the tube wall. An analysis of the experimental data shows that the gain-saturation parameter increases with current density.     

Gas dynamic CO2-He-(N2) laser investigations

Experiments on IR laser action and gain measurements are reported for a CO2-containing gas mixture flow that cools as a result of expansion. The mixture is preheated by a reflected shock wave, and the gas is expanded into a vacuum through a slit. Laser action is obtained in a CO2-He mixture, while the addition of nitrogen increases the gain. The gain was found to depend on the distance from the slit and the gas pressure before the slit.     

Electron energy distribution in CO2laser discharges

Electrical plasma parameters of the CO2laser were investigated by probe and high-frequency techniques. The electron energy distribution function was measured by the second derivative method. The relatively high-pressure effect on the electron probe current was taken into account when analyzing the experimental curves. The influence of the addition of N2, He, Xe and the influence of CO2dissociation on the plasma discharge properties were studied. Calculations of the pumping rates to vibrational levels taking part in creating inversion show that the influence on output power of a CO2laser usually observed with the addition of N2and He cannot be explained by a changing of the electron component of the plasma. The increase of output power and efficiency with addition of Xe to the CO2laser is connected with an essential changing of plasma parameters of the electron component.     

A stacked Blumlein N2laser

A novel device for producing fast-rise-time, large-volume electrical-discharge excitation of gas lasers is described. Some operating characteristics of an N2ultraviolet (UV) laser are presented.     

Resonantly enhanced 26 GHz parametric upconversion of CO2laser in NH3

Resonantly enhanced three-wave mixing of the 10.784 μmR(18) line of the C¹³O2¹⁶laser and microwave radiation at 26.378 GHz in Stark tunable N¹⁴H3has resulted in upconverted parametric output at 10.774 μm. The energy levels of N¹⁴H3involved in the interaction and the apparatus used in the experiment are described. Experimental results showing saturation of the parametric signal with increasing N¹⁴H3pressure, input microwave power, and input laser power are described.     

Excitation of an atmospheric-pressure CO2-N2-He laser by capacitor discharges

The design of a new type of atmospheric pressure CO2-N2-He laser capable of producing 1.2-J infrared light pulses with a peak power of 0.5 MW is described. An investigation of the laser output dependence on gas flow, gas mixture, capacitor voltage, output coupling reflectivity, and electrode spacing was made. It is shown that even greater energies and powers should be possible at higher voltages and larger electrode gaps.     

A pin-electrode atmospheric-pressure CO2laser

A 1.2-m-long transversely excited atmospheric-pressure (TEA) CO2laser utilizing shower discharges is described and its operating characteristics as a function of voltage examined up to 60 kV. Pulse energies in excess of 2 J, peak powers in excess of 20 MW, and efficiencies up to 15 percent have been achieved.     

Q-switching of the CO2laser

The laser pulses obtainable from aQ-switched CO2laser are calculated and compared with the results of a number of different techniques of performing theQ-switching. The continuously operating laser is considered first. The transition rates between the molecular vibrational states and their occupations are derived from the measured CW power. The laser tube was 1.9 meters long, had a diameter of 2.4 cm, and used flowing CO2-N2-He gas. For rapidQ-switching, maximum pulses of 4.5 mJ energy and 85 ns half width are predicted. Such pulses were observed with a rotating mirrorQ-switch. However, that technique has a limited pulse repetition rate and experiments on closely spaced pulses are difficult to interpret. A more flexible technique, which allows a much greater variation in the experimental parameters, is the use of a fast shutter to interrupt the laser beam in the cavity. While this switch is somewhat slower than the rotating mirror it does produce pulses of the same energy at repetition rates up to 5000 per second, and smaller pulses at any desired higher rate. From these measurements the upper and lower laser level lifetimes are deduced. They are found to agree well with the values obtained from the CW measurements.     

PassiveQswitching of a CO2laser near 9.2 µ using CF2Cl2

CF2Cl2is found to cause passiveQswitching on practically all of the lines in theRbranch of the00deg1-02deg0vibrational-rotational band of CO2.     

A radiatively pumped CW CO2laser

A proof of principle experiment to demonstrate the physics of a radiatively pumped laser has been carried out. For the first time, a blackbody cavity has optically pumped a CW CO2laser. Results are presented from a series of experiments using mixtures of CO2, He, and Ar in which maximum output power was obtained with a 20 percent CO2- 15 percent He-65 percent AR mixture. The dependence of the output power on the blackbody temperature and the cooling gas flow rate is also discussed. By appropriately varying these parameters, continuous output powers of 8-10 mW have been achieved.     

A high-power CO2laser radar transmitter

Experiments on the amplification of CW and pulsed infrared signals at 10.6-μ, wavelength have been carried out on CO2laser amplifiers excited by dc and pulsed electrical currents. Measurements of low signal gain, gain saturation, repetitive pulse amplification, and optical distortion have led to the design of a 1-kW average power transmitter with 10-μs infrared output pulses. The design, construction, and performance of this device are discussed. Measurements of pulse shaping, pulse-to-pulse stability, output beam divergence, and stability are outlined.     

Additional CW far infrared laser lines from CO2laser pumped cis 1,2 C2H2F2

Six new CW far infrared laser lines are reported for the cis 1, 2 C2H2F2molecule optically pumped by a CO2laser. Of these, two have high conversion efficiencies in the 1-2 percent range.     

Initiation of NF3-H2chemical reactions via CO2laser irradiation of NF4BF4

NF4BF4has been irradiated with a low-power CO2laser to produce reactive species which then initiate reactions in an ambient NF3-H2mixture. The laser-induced decomposition of NF4BF4in vacuum was measured as a function of laser power and energy. The laser-induced decomposition threshold was determined to be 40 mJ, which corresponds to a laser fluence of 20 J/cm². This same value was determined for the initiation threshold of NF3-H2reactions via CO2laser irradiation of NF4BF4. Visible and infrared emissions were observed from initiated NF3-H2mixtures. This radiative technique has attractive features for initiating reactions in solid-gas systems.     

Computer solution for the traveling-wave-excited N2laser

A computer solution is presented for the nitrogen laser excited by a longitudinal relativistic electron beam. The solution demonstrates efficient extraction by amplified spontaneous emission, and preferential radiation parallel to the electron beam, caused by the traveling-wave nature of excitation. These observations tend to validate approximations used to calculate extraction in an earlier study.     

Photopreionization of the 3371-Å pulsed N2laser

Photopreionization of the 3371-Å pulsed N2laser by use of a seed gas of low ionization threshold and flashlamp excitation is observed to result in increased laser output and reproducibility. Preionization also increases the range of permissible operating pressures, enabling operation with atmospheric-pressure mixtures of N2and He without reduced intensity.     

A simple self-mode-locked atmospheric pressure CO2laser

The construction and operation of a particularly simple atmospheric pressure CO2laser that uses a fast voltage doubling is described.     

Compact, high-power FIR NH3laser pumped in a CO2laser cavity

A compact CO2-NH3FIR laser system, with an NH3laser cavity inserted in the pump CO2laser cavity, was designed. Temporally smooth and reproducible single mode NH3laser pulses with an energy of 5 mJ (20 kW peak power) were obtained at the 152 μm line when optically pumped by the injection-locked single-mode CO2laser with a pulse energy of 0.3 J.