A. J. Alcock

High-efficiency diode-pumped Nd:YVO 4 slab laser

Optical-to-optical conversion efficiencies of as high as 32% with a slope efficiency of 44% were obtained with a novel diode-bar, side-pumped laser cavity design. A slab geometry with a single, high-angle-of-incidence reflection was used to extract gain from near the pump face of a Nd:YVO(4) bar that absorbed strongly at the pump wavelength. Small-signal gains of greater than 8 cm(-1) and pulse energies of as much as 3.2 mJ were obtained in an almost TEM(00) mode. Aperturing effects by the laser rod were found to limit the effects of nonuniform gain on the laser mode.

Continuously tunable high‐pressure CO2 laser with uv photopreionization

The operation of a uv photoinitiated tranverse‐discharge CO2 laser has been investigated at pressures up to 15 atm. Preliminary studies of a device having an active volume of [inverted lazy s] 13 cm3 have yielded a maximum output of [inverted lazy s] 1 J in 30 nsec, while the use of a grating‐tuned resonator has resulted in continuously tunable operation over frequency intervals of [inverted lazy s] 20 cm−1.

A 300-J multigigawatt CO 2 laser

The development of a new transverse electric discharge scheme has permitted the excitation of large volumes of CO 2 , N 2 , and He mixtures with beam cross sections up to 60 cm2in area. The scheme utilizes as a preionizer a sheet of small arc discharges produced prior to the main discharge and situated behind a perforated anode. Time-resolved photography establishes that rapid volumetric ionization of the gas between the electrodes occurs concurrent with the formation of these arcs. This behavior is consistent with a preionization mechanism depending upon UV photo-excitation of the gas. A parametric study has shown that reproducible discharge conditions in 30 percent CO 2 gas mixtures are obtained with input energies of >300 J.I-1, resulting in energy extraction efficiencies of ∼10 percent and an average small-signal gain of ∼4.3 percent cm-1. The laser is modular in construction and, when a number of discharge modules are employed in series in a simple oscillator configuration, energies of ∼300 J with peak powers of several gigawatts are obtained.

IMAGE‐CONVERTER STREAK CAMERA WITH PICOSECOND RESOLUTION

A streak camera incorporating a standard, readily available, image‐converter tube has been developed and used for the direct measurement of 1.06‐μ‐wavelength picosecond pulses generated by a mode‐locked neodymuim: glass laser.

A fast scalable switching technique for high‐power CO2 laser radiation

Fast switching of high‐power 10‐μm radiation by reflection from optically induced carriers in polycrystalline germanium has been demonstrated. Initial studies carried out with a single‐mode TEA CO2 laser and a 2‐nsec ruby laser pulse have resulted in the generation of synchronized ∼2‐nsec pulses of 0.69‐ and 10‐μm wavelength. Potential applications of this technique include the selection of single high‐energy pulses from the mode‐locked output of large‐aperture CO2 lasers.Fast switching of high‐power 10‐μm radiation by reflection from optically induced carriers in polycrystalline germanium has been demonstrated. Initial studies carried out with a single‐mode TEA CO2 laser and a 2‐nsec ruby laser pulse have resulted in the generation of synchronized ∼2‐nsec pulses of 0.69‐ and 10‐μm wavelength. Potential applications of this technique include the selection of single high‐energy pulses from the mode‐locked output of large‐aperture CO2 lasers.

Generation and detection of 150‐psec mode‐locked pulses from a multi‐atmosphere CO2 laser

Mode‐locked operation of a uv‐preionized TE CO2 laser has been investigated at pressures in the 10–15‐atm range. By upconverting the output to 0.96 μm and recording it with a streak camera it has been shown that pulses of duration less than 150 psec can be generated using p‐type Ge saturable absorbers.

High-repetition-rate diode-pumped Nd:YVO4 slab laser.

Q-switched pulse energies of approximately 1 mJ at repetition rates as high as 1 kHz have been obtained from an electro-optically Q-switched Nd:YVO4 slab oscillator that was side pumped by a five-bar diode-laser stack. High gain within the slab resulted in pulse durations of less than 5 ns and sub-15-ns buildup times. Thermal effects caused the beam profile to deteriorate gradually from diffraction limited at lower repetition rates to approximately 1.5 times diffraction limited at 1 kHz.

Preionization kinetics of an X-ray preionized XeCl gas discharge laser

The influence of preionization conditions on the performance of a XeCl gas discharge laser preionized by a short, high intensity x-ray pulse, has been studied. The laser output energy and optical pulse temporal characteristics have been used to determine the roles of initial electron density and of electron attachment to HCl and to impurities. Although the short pulse preionization technique functions well for XeCl when the laser voltage pulse has a short risetime (≲20 ns), it is less well suited to XeCl lasers using slowly rising voltage pulses (>50 ns), or to F2 containing gas mixtures (KrF and XeF lasers).

Spatially resolved gain measurements in UV preionized homogenous discharge XeCl and KrF lasers

Spatially uniform avalanche discharges of relatively long duration have been obtained in a UV‐preionized, high‐pressure, rare‐gas–halide laser. In the case of XeCl pulse durations as long as 70 ns have been observed. The spatial distribution of the small‐signal gain in a plane transverse to the laser axis has been measured. The active discharge cross sections with better than 90% gain uniformity were 2.8×3.0 and 2.8×2.5 cm2 for XeCl and KrF, respectively. The use of neon rather than helium as a buffer gas increased the discharge cross section, and the laser pulse duration resulting in improved laser output energy densities of 4.5 J/l in XeCl and 2.8 J/l in KrF.

A Simple Laser‐Triggered Spark Gap with Subnanosecond Risetime

The construction and operating characteristics of a pressurized laser‐triggered spark gap capable of switching voltages exceeding 10 kV with a risetime of less than 300 psec are described. Other desirable features are its low delay and jitter times (∼1 nsec), the ability to deliver rectangular pulses with less than 10% ripple during and after the pulse, and its simplicity of construction. The gap has been investigated using the output of either a single mode ruby laser or a mode‐locked neodymium‐glass laser as a trigger.