Lelland A. C. Weaver

Copper superradiant emission from pulsed discharges in copper iodide vapor

Superradiant copper laser emission at 5106 and 5782 A is reported from pulsed discharges in copper iodide vapor at temperatures of about 600°C. Dissociation of the iodide, excitation of the copper atom, and resonance trapping of the 3248 A copper transitions are proposed as the principal inversion mechanisms.

High‐repetition‐rate copper iodide laser

Quasicontinuous pulsed laser output at 5106 and 5782 A is reported from 600°C copper iodide discharges at repetition rates near 8 kHz. In single pulses 35 μJ cm−3 has been observed, indicating that 0.28 W cm−3 volumetric power density can be achieved.

Kinetic processes in continuously pulsed copper halide lasers

Absorption measurements in the afterglow of electrically excited copper halide laser mixtures are described. Ground state and metastable copper density decay rates determine the optimum delay for application of a second electrical pulse. Output energy densities of 45 μJ . cm-3have been observed for single-pulse conditions. Gas temperature increases limit the electrical pulse energy which can be applied on a continuous basis, and in this regime the output energy density is reduced to \sim 11 \mu J . cm-3due to the decreased pulse energy and cumulative population effects. Thermal gradients and radial cataphoresis are suggested as explanations for observed transient effects in the multipulse output envelope. Average 5106 A power levels of 1.34 W at 0.3 percent efficiency were observed within 18 kHz burst-mode pulses applied at low duty cycle.

Superradiant emission at 5106, 5700, and 5782 Å in pulsed copper iodide discharges

Superradiant laser emission at 5106, 5700, and 5782 A is reported from pulsed discharges in copper iodide vapor at temperatures near 600°C. This conclusion is supported by pulse shortening of the visible emission and a marked increase in the relative visible intensity compared to the copper resonance radiation as the critical temperature range is approached. Electrical dissociation of the copper iodide, electron impact excitation of the copper atoms, and radiation trapping of the 3248- and 3274-A resonance lines are proposed as the principal inversion mechanisms. Below \sim450\deg C, where insufficient copper iodide is vaporized to provide resonance trapping, the upper laser level lifetimes are ∼10 ns, whereas at higher temperatures trapping is complete and the effective2P 3/2 and2P 1/2 lifetimes are 615 and 370 ns, respectively. The reservoir temperature at which stimulated emission is observed is in good agreement with calculations of the threshold ground-state copper densities required for resonance trapping. These experiments indicate that practical copper laser systems operating at substantially reduced temperatures can be developed provided instabilities in the copper iodide discharges can be overcome.

High average power pulser design for copper halide laser systems

A circuit using two thyratrons is described which provides alternating polarity, high‐current pulses at pulse repetition rates up to 20 kHz, suitable for operating copper halide lasers. The circuit is a modification of a Blumlein configuration in which two networks are charged in parallel and discharged in series, providing a voltage quadrupling effect when used with resonant charging. By triggering the thyratrons sequentially the current is reversed on alternate pulses, which greatly reduces axial cataphoretic effects and extends the laser tube operating lifetime. The circuit can deliver up to 5 kW average power at 15 kHz.

Long‐lived lead‐vapor lasers

Lead‐laser operation has been demonstrated at 7229 A in all‐hot sealed‐off quartz discharge tubes for 50‐h cumulative operating times without tube degradation or failure. The maximum output energy of 230 μJ or 2.0 μJ cm−3 was obtained at ∼1.5 kHz, and the discharge efficiency was 0.12%. Average‐power levels of 750 mW at 6 kHz were maintained under burst mode excitation conditions for extended periods at temperatures of ∼1050 °C. Lead‐laser emission at ∼500 °C was also obtained using lead iodide as the starting material.

Axial cataphoresis effects in continuously pulsed copper halide lasers

It has been observed in a continuously pulsed copper halide laser that laser performance deteriorates rapidly due to axial cataphoresis effects. Dissociated copper ions are pumped cataphoretically toward the cathode by the applied electric field, causing nonuniform laser discharges and preferential copper condensation near the cathode. These effects can be eliminated experimentally by alternating the polarity of the applied voltage either mechanically or electronically. This improvement permits long‐lived copper halide laser operating at average power levels in the 1–10‐W range.

Discharge scaling studies for a continuously operating fast flow electrically excited (COFFEE) laser

electron-beam-ionization.2 This scheme, similar to one used previously by J. P. Reilly3 and A. E. Hill: differs from previous work, in that, in the present device the proximity of metal and insulating waveguide walls play an important role in discharge preionization, stabilization, and cooling. A 10 cm long waveguide TE COz laser, based on this excitation scheme, should be capable of generating CW output powers in the range 10-100 watts. A hollow waveguide of 1 mm2 cross-section was constructed with slabs of fused quartz and metal in such a way that multiple transverse discharges could be formed inside the waveguide. A solid block of polished copper comprised one wall of the waveguide. A sandwich made up of alternate slabs of aluminum and quartz (each 1 mm thick) comprised the opposite waveguide wall. The remaining waveguide walls were formed by fused quartz slabs whose edges had been polished. A train of 20 nsec duration high-voltage pulses (4-8 kV) applied (transverse to the waveguide axis) between the aluminum slabs (acting as cathodes) and the copper block (acting as an anode) increases the electron density from a low initial value (left over from the previous pulse) to a high peak value (1-3 x 10 ~ m ~ ) . This high level of ionization is thought to result from a combination of efficient secondary emission from the aluminum cathode (the Malter effect) and electron multiplication due to the high electric fields present. After the ionizing pulse, a continuous electric field applied between the aluminum slabs (now acting as anodes) and the copper block (now acting as a cathode), with E/P = 3.5 6.5 V/cm-torr, provides the electron energy needed to vibrationally excite N, and COz molecules during the recombination period. This electric field results in energy loadings from 50 to 500 J/L-atm without arc breakdown and values for peak gain from 1.2 to 6.6%/cm. The gain rises to this peak value some 70 psec after the start of the ionizing pulse and has an overall duration of 150 psec. Hence, at pulse repetition frequencies of 5-10 kHz nearly continuous gain can be obtained. A comparison of the peak gain coefficient versus E/P for the present device and for an electron-beam-controlled discharge, is shown

The Application of Lasers to Industry

The recent increase in energy output, average power, and reliability of some lasers has made them worthy of consideration for manufacturing operations. Pulsed lasers can be used for hole punching and spot welding. Low-power continuous output gas lasers can be used for a wide variety of applications, including optical alignment, interferometric precision measurements, and measurements of fluid flow velocity. Other continuous output lasers, such as the carbon dioxide gas laser, are capable of power outputs in excess of 103 watts at greater than 10 percent efficiency and can be used to cut materials in unique ways. Lasers show particular promise for use in automated operations, and the use of a light beam as a cutting agent eliminates the need for maintenance such as cleaning and sharpening.