J. B. Gerardo

De‐excitation rates for excited xenon molecules

The time decay of the density of excited xenon molecules (Xe2*) in the lowest bound diatomic states was monitored by observing the photons (1730 ± 100 A) emitted in transitions to the repulsive ground state. Mutual ionizing collisions of the excited diatomic states are responsible for the initial decay at high excited‐state density. The measured rate for this process is (3.5 ± 1.4) × 10−10 cm3 sec−1. At lower excited‐state densities, the decay of Xe2* is controlled by spontaneous emission [(20 ± 8) × 106 sec−1], collisional deactivation [(3,3 ± 1.3) × 10−18 cm2], and electronic recombination.

Diluent cooling of a vacuum‐ultraviolet high‐pressure xenon laser

Experimental results are presented on the effect of diluent cooling of a 1721‐A high‐pressure xenon laser produced with a pulsed beam of high‐energy electrons. Both helium and argon were used as diluents in order to limit the rise in the gas temperature that occurs when the electron beam is stopped in the gas. In the Xe–He mixtures the chemistry was not significantly altered by the presence of He; but in the Xe–Ar mixtures, argon was very important in the absorption and transfer of internal electronic energy. The results demonstrate that both diluents improve the operational characteristics of the laser. Only helium is found to improve the efficiency of conversion of electron‐beam energy into stored laser energy.

Intense‐electron‐beam excitation of the 3371‐Å N2 laser system

The results of a parametric study of superradiant laser action at 3371 A in the second positive band system of molecular nitrogen with excitation by a high‐energy electron beam are reported. Efficiency up to 0.15% was observed for conversion of electron‐beam power to laser power at 3371 A. Laser output power up to 24 MW in a 6‐nsec pulse was observed.

1730‐Å radiation dominated by stimulated emission from high‐pressure xenon

Experimental data are presented which demonstrate superfluorescent radiation due to stimulated transitions between the lowest‐bound diatomic states of xenon and the repulsive ground state. In this context, superfluorescence describes a condition where, even in the absence of feedback, radiation from the fluorescent medium is dominated by stimulated transitions. The continuum emission spectrum was highly anisotropic and narrowing of the spectrum was observed. The optical gain was greatest at a wavelength of 1730 ± 10 A, where the experimentally estimated effective gain cross section is 1 × 10−18 cm2.

Xenon-dimer-laser net-gain measurements

The gain of the vacuum‐ultraviolet xenon‐dimer laser was evaluated by employing a double‐pass technique with spectral filtering of the probe radiation. At the wavelength center of the continuum‐emission spectrum (λ0 ?1720 A), the net‐gain coefficient at pressures less than 1.1×104 Torr was found to be g0= (1.05±0.2) ×10−25Ps cm−1, where Ps is the spontaneous‐emisssion intensity of the continuum‐emission band in units of photons/sec cm3. By comparison of laser‐output waveforms with temporally resolved net‐gain measurements, it is shown that the laser intensity is limited by an unidentified time‐dependent loss mechanism that is either foreign to the excited medium or that is driven by the laser radiation. While we do not know the source of this mechanism, our observations show that this time‐dependent loss mechanism is not associated with the lasing states of the xenon dimer. At very high pressures (≳1.3×104 Torr) the effects of photoscattering by the background xenon were found to reduce the value of g0.

Comment on ’’Dynamic model of high‐pressure rare‐gas excimer lasers’’

The model of the rare‐gas excimer lasers that was recently proposed by Werner et al. is shown to be inconsistent with some experimental measurements of xenon dimer laser gain and laser intensity. Measurements of the laser intensity and laser‐medium gain of a xenon dimer laser show that the laser pulse terminates well before the laser‐medium gain falls below the prelasing losses of the optical resonator. The measured value of the stimulated‐emission cross section for the xenon dimer laser is (1.05±0.2) ×10−25 A cm2 at 1720 A, where A is the transition probability of the upper energy level of the laser.

Excitation and Ionization Rates in Hydrogen at Very High E/n

We will report time-dependent electron density and excited state density measurements at very high E/n with a temporal resolution of 1 nsec. We create electron avalanching in gases of interest using a fast-rising (3–6 nsec) microwave (S-band) pu1se, while simultaneously monitoring the electrondensity with a low-power, S-band probe signal. This latter signal is in an interferometer configuration having sufficient sensitivity to monitor densities as low as ≅106 cm–3. The avalanche ionization takes place in a quartz cell contained in the S-band waveguide and having no electrodes or externally applied fields, except for a longitudinally applied magnetic field tuned to electron-cyclotron resonance at the high-power pulse frequency. The equivalent effective field under these conditions reduces to a DC field at one-half the peak value.

Vacuum-ultraviolet noble-gas dimer lasers

An experimental investigation was made of the shape and intensity of light pulses emitted by an Xe2* laser excited by a relativistic electron beam. The results obtained were used to deduce the line profile and the gain in excited xenon. The authors suggest that the majority of the results obtained should be applicable also to other noble-gas dimer lasers.