Edward L. Patterson

Energy extraction from a large‐volume HF laser amplifier

Energy extraction from a large‐volume HF laser amplifier has been measured as a function of input intensity. Both the oscillator and amplifier were operated with similar gas mixtures of H2 and F2, which assured a good spectral match between the oscillator and amplifier. The amplifier input intensity was varied from 104 to 2×107 W/cm2. An input intensity of 2×107 W/cm2 extracted an energy equal to about 90% of the energy extracted from the amplifier when it was operated as an oscillator. The experiment also demonstrated that an input intensity of 104 W/cm2 decreased the amplified spontaneous emission intensity by a factor of 2 from the value with no input. Increasing the input intensity level above 104 W/cm2 did not further reduce the amplified spontaneous emission.

A study of an electron-beam excited atomic xenon laser at high energy loading

Operation of an electron-beam excited atomic xenon laser was investigated at pump rates between 40 W/cm/sup 3/ and 1 kW/cm/sup 3/ with pump times of 1 ms. Effects of cavity loss, gas mixture, and pump rate on laser performance were studied under selected conditions. The variation in laser power in 99.5% argon and 0.5% xenon selectively lasing at 1.73 or 2.6 mu m was investigated as a function of pump power. It was found that the laser pulsewidth was shorter than the pump pulse and increased as the pump rate decreased, consistent with a temperature-induced effect. Lasing with broadband optics was investigated as the xenon concentration was varied and as helium or neon was combined with argon-xenon mixtures. Strong lasing was observed for xenon concentrations up to 20%. Addition of helium resulted in a slight increase in laser pulsewidth and caused lasing at 2.03 mu m to increase at the expense of lasing at 1.73 and 2.6 mu m. >

Electron‐beam uniformity of a large‐area high‐current accelerator diode

Time‐resolved photography of Cherenkov emission has been used to study large‐area electron‐beam uniformity and electron‐beam propagation in air. For the 50‐ns pulse widths used, we show that the time‐dependent electron emission from large‐area cathodes is typically very nonuniform. Pinching of the electron beam by its self‐magnetic field can be prevented by the use of an applied axial magnetic field approximately equal to the self‐magnetic field generated by the electron beam. When an applied field is used, beam nonuniformities introduced by the anode support structure persist through tens of centimeters of air outside the diode. These nonuniformities can reduce efficiency and beam quality of the laser. Beam rotation in the diode caused by the applied magnetic fields can result in significant loss of electron‐beam energy to the anode chamber and foil‐support structure. However, we have shown that emission can be reduced on areas of the cathode which map onto obstructions on the anode so the electron energ...

TA4 - Characteristics of a high-energy hydrogen fluoride (HF) laser initiated by an intense electron beam

The characteristics of a high-energy hydrogen fluoride (HF) laser and the effects of optical elements on beam quality and on energy extraction are described. The HF laser is initiated by injecting a 2-MeV electron beam into a mixture of SF6and C2H6. With 300-torr SF6and 30-torr C2H6, the radiated energy with a flat mirror on one end of the laser cell is ≈80 percent of the two-way energy when no mirrors are used. The effect of a confocal unstable resonator in providing collimation of the laser beam was studied. The maximum laser energy measured was 380 J in a 23-ns full width at half maximum (FWHM) pulse. The maximum electrical efficiency measured was 14 percent, which is about 60 percent of the maximum theoretical value.

Laser‐beam characteristics of Phoenix, an HF oscillator‐amplifier system

Energy‐extraction and beam‐quality measurements are reported for Phoenix, Sandia’s high‐energy HF laser system. The final amplifier in this oscillator‐amplifier chain used electron‐beam initiation of high‐pressure gas mixtures of H2‐F2‐O2. The oscillator and preamplifier utilized fast electric discharges in SF6‐HI mixtures. Energy‐extraction efficiency using this oscillator system was the same as that previously determined using an H2‐F2‐O2‐fueled oscillator which produced a better spectral match to the amplifier but which yielded poorer beam quality. Lateral shearing interferograms showed no significant phase‐front degradation of the beam by the final amplifier. Pinhole energy‐transmission measurements using a short‐focal‐length parabolic mirror determined that the focal‐spot diameter was 2.7 times the diffraction‐limited diameter.

Long‐pulse, electron beam pumped, atomic xenon laser

Characteristics of a long‐pulse, low pump rate, atomic xenon (XeI) laser are described. Energy loading up to 170 J/L at pulse widths between 5 and 55 ms is achieved with an electron beam in transverse geometry. The fraction of energy in each wavelength obtained with electron beam pumping is in good agreement with results from fission fragment pumping in a reactor pumped laser. Values for the small‐signal gain coefficient, loss coefficient, and saturation intensity as a function of pump rate are presented. Laser energy as a function of pulse width and the effects of air and CO2 impurities are described. An investigation of the dominant laser wavelength in a high‐Q cavity indicates that the 2.6 μm radiation dominates.

Spectral and bandwidth characteristics of a high-pressure Xe laser in a several kilogauss field

A technique based on the Zeeman effect has been developed for determining the gain bandwidth of the 1.73- mu m laser line of the high-pressure atomic xenon laser. A bandwidth in the range of 0.14 to 0.37 cm/sup -1/ has been determined by this method. Lasing bandwidths for the 1.73-, 2.03, 2.63, and 2.65- mu m lines have also been determined for pump rates in the range 0.3 to 1.8 kW/cm/sup 3/. The effect of the magnetic field on the spectral characteristics of these lines is also given. >

Study of energy deposition in the electron‐beam‐pumped laser facility HAWK

The HAWK facility has been developed as a tool to investigate the kinetics of electron‐beam‐pumped lasers at a pressure of 1 atm for pump rates of 0.040–1 kW/cm3 and pump times of 0.05–1 ms. The highly collimated (1 cm FWHM within the lasing medium) relativistic electron beam propagates through fast valves that separate the accelerator vacuum from a 2‐m‐long vacuum isolation section, a 0.4‐m‐long gas‐filled buffer section, and 0.7 m along a lambda‐geometry laser cell. A 6.5 kG magnetic field confines the 1‐MeV electron beam laterally and guides it around a 30° bend into the 3.3‐cm‐diam laser cell. A magnetic mirror at the far end of the laser cell reflects a large portion of the transmitted electron beam, thereby protecting the laser optics from the electron beam and making the axial deposition more uniform. In this paper we describe modeling of the electron beam energy deposition in HAWK using the three‐dimensional Monte Carlo electron/photon transport code acceptm and compare our results with the measur...

High Energy Hf Pulsed Lasers

Recent experiments show that pulsed HF lasers are capable of producing high energy with good efficiency. Preliminary experiments show that the laser radiation from the high-gain medium can be controlled with a low-power probe laser beam or with low-level feedback. These results indicate that the HF laser may have potential for second-generation laser fusion experiments.