Chi-sheng Liu

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.

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.

Chemical control of HgBr lasers

The selection of electrode and laser materials for long life operation of HgBr lasers is discussed. The results of thermochemical considerations in conjunction with experimental life tests to evaluate suitable materials indicate that gold-plated nickel is inert to HgBr laser gases. A HgBr 2 constitution system using MoBr 2 as a bromine source to take care of unavoidable areas that are not plated in a gold-plated nickel laser has been installed to extend the operating life of a HgBr laser to more than 108shots without any degradation in performance.