G. N. Hays

Measured laser parameters for reactor‐pumped He/Ar/Xe and Ar/Xe lasers

We have measured laser parameters for reactor pumping of He/Ar/Xe gas mixtures lasing predominantly at 2.03 μm and Ar/Xe mixtures lasing predominantly at 1.73 μm. Gains as high as ∼3%/cm have been measured in He/Ar/Xe at pump powers of ∼200 W/cm3 . Both systems exhibit small distributed losses. Intrinsic laser energy efficiencies as high as 2.4% (3.0%) have been observed for He/Ar/Xe (Ar/Xe). These efficiencies are the highest reported for reactor‐pumped lasers.

The effects of He addition on the performance of the fission‐fragment excited Ar/Xe atomic xenon laser

The intrinsic power efficiency of the atomic xenon laser depends upon the electron density because of the mixing of the laser levels by electron collisions while the electron density in high‐pressure particle‐beam excited plasmas increases with increasing gas temperature. Therefore, in order to reduce the amount of electron collisional mixing when operating at high‐energy loadings (≳100’s J/1‐atm) mixtures having a high‐heat capacity are required. In particle‐beam excited Ar/Xe mixtures, which typically yield the highest intrinsic laser efficiencies, increasing the gas pressure to increase the heat capacity is not always practical due to the high‐stopping power of the gas mixture. For this reason we have experimentally and theoretically investigated adding He to Ar/Xe mixtures in studies of a fission‐fragment excited atomic xenon laser. Adding He increases the heat capacity without appreciably perturbing the favorable kinetics resulting in efficient operation of the laser in Ar/Xe mixtures. We find that w...

Predictions for gain in the fission‐fragment‐excited atomic xenon laser

The infrared atomic xenon laser (5d→6p) is an attractive candidate for fission fragment excitation, which provides low‐power deposition (1–100 W cm−3), long pulse lengths (1–10 ms), and high‐energy deposition (100s J l −1). Optical gain at 1.73 and 2.03 μm has recently been measured in a reactor‐excited xenon laser yielding values exceeding 0.03–0.05 cm−1 at power depositions of less than 10s W cm−3. Gain was also found to rapidly terminate before the peak of the pump pulse for some experimental conditions. A computer model has been developed to predict gain in fission‐fragment‐excited xenon lasers and these experiments have been analyzed. It is found that the termination of gain is most likely attributable to gas heating which increases the electron density, leading to electron collision quenching. The specific dependence of gain on pump rate suggests that a reduced rate of recombination of molecular ions with increasing gas temperature is partly responsible for this behavior.

A study of the 0.634 μm dimol emission from excited molecular oxygen1

Abstract The rate constant, k d , for the process 20 2 ( 1 Δ) - 20 2 ( 3 Σ) + hv was determined for radiation at 0. 634 μm. It was found that at room temperature k d = (4.4 ± 1.3) × 10 −23 cm 3 molecule −1 s −1 and that k d is independent of pressure for oxygen pressures up to 4.5 Torr and argon pressures up to 77 Torr.

Fission‐fragment excited xenon/rare gas mixtures. I. Laser parameters of the 1.73 μm xenon transition

Laser parameters for the 1.73 μm (5d[3/2]1−6p[5/2]2) xenon transition in fission‐fragment excited Ar/Xe, He/Ar/Xe, Ne/Ar/Xe, and He/Ne/Ar/Xe gas mixtures are presented. Using a cw F center laser, time resolved small signal gain was probed as a function of total pressure, xenon concentration, pump power, He/Ne/Ar buffer ratio and impurity concentration. Small signal gains of up to 2%/cm were observed for pump rates of 30 W/cm3. Addition of helium and/or neon to the argon buffer increased the width of the time resolved laser gain pulse and reduced the absorption observed under some experimental conditions. Experimentally determined gain scaling laws for several gas mixtures are presented. The measured small signal gain was coupled with the results of laser cavity measurements to calculate the saturation intensity for several gas mixtures. The addition of helium or neon increases the saturation intensity for several gas mixtures. Laser cavity measurements as well as the gain × saturation intensity product in...

Parametric investigation of the fission-fragment excited helium/argon laser at 1.79 μm

Characteristics of the fission‐fragment excited helium/argon laser operating on the 1.79‐μm (3d[1/2]0,10−4p[3/2]1,2 argon transition are presented. Laser output occurs for approximately 80% of the 0.9 to 3 ms full width at half maximum thermal neutron pump pulse. Output power efficiency optimizes for a total gas pressure of 760 Torr and argon concentration of 0.3% to 2.0%. Power efficiency was 1.4%±0.4% for instantaneous pump rates of 45 to 230 W/cm3. The small signal gain and saturation intensity for instantaneous pump rates of 30 to 90 W/cm3 are 0.55% to 1.05%/cm and 70 to 110 W/cm2, respectively. The laser threshold as a function of helium pressure and argon concentration will be presented. The advantages of fission‐fragment excitation in predominantly helium gas mixtures will be discussed.

Fission‐fragment excited xenon/rare gas mixtures. II. Small signal gain of the 2.03 μm xenon transition

The results of small signal gain measurements of the 2.03 μm (5d[3/2]1−6p[3/2]1) xenon transition in fission‐fragment excited Ar/Xe, He/Ar/Xe, Ne/Ar/Xe, and He/Ne/Ar/Xe gas mixtures is presented. Time resolved small signal gain was probed using a cw He/Xe discharge laser as a function of total pressure, xenon concentration, pump power, He/Ne/Ar buffer ratio, and impurity concentration. Small signal gains of up to 6%/cm were observed for pump rates of 15 W/cm3. Addition of helium and/or neon to the argon buffer increased the width of the laser gain and reduced the absorption observed under some experimental conditions. Experimentally determined gain scaling laws for several gas mixtures are presented.

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.

Laser efficiency and gain of the 1.73 μm atomic xenon laser at high He/Ar buffer gas ratios

Addition of helium to an Ar/Xe gas mixture has been shown to significantly improve the fission‐fragment excited 1.73 μm atomic xenon laser performance. Using narrow band dielectric laser cavity mirrors to suppress the 2.03 μm atomic xenon transition, the 1.73 μm laser power efficiency varied between 1% and 3% for total pressures of 520–1550 Torr, He/Ar ratios of 3/1–16/1, and pump rates of 5–40 W/cm3. For a constant energy loading, the FWHM of the laser pulse with respect to the pump pulse increased by a factor of 2.5 when argon was replaced by helium. Small signal gain varied between 0.1%/cm and 1.0%/cm. The implication of helium substitution on the Ar/Xe laser kinetics is discussed.

Control of HF laser output spectrum using selective intracavity loss

It is shown experimentally that the addition of gas‐phase absorbers into the cavity of a small pulsed HF laser reduces the number of lasing lines, without seriously reducing output energy, for 200‐ns FWHM laser pulses. This effect is discussed in terms of the rapid rotational relaxation characteristic of gas‐phase HF and the fact that the losses introduced are frequency selective.