S. J. Thomas

Deuterium separation at high pressure by nanosecond CO2 laser multiple‐photon dissociation

Photochemical deuterium separation is evaluated at pressures up to 1 atm using 2 ns duration CO2 laser pulses to achieve multiple‐photon dissociation (MPD) as the isotopic separation step. Photochemical performance is compared for Freon 123 (2,2‐dichloro‐1,1,1‐trifluoroethane), difluoromethane, and trifluoromethane based on deuterium optical selectivity in absorption, photoproduct yield, and single‐step deuterium enrichment factor. The absorption coefficient versus energy fluence is measured from 0.01 to 3 J/cm2 fluence for CF3CDCl2, CDF3, and CHDF2; added buffer gas results in an order‐of‐magnitude increase in the CDF3 absorption coefficient. The deuterium optical selectivity in absorption at 0.5 J/cm2 fluence with added buffer is 80 for CF3CDCl2 at 10.65 μ, 800 for CHDF2 at 10.48 μ, and 2500 for CDF3 at 10.21 μ. The absorption coefficients and hence optical isotopic selectivities are dependent on fluence, and the optical selectivity attains a maximum value of 8000 for CDF3 below 0.01 J/cm2 fluence. The ...

Effect of oxygen on flashlamp-pumped organic-dye lasers

Dissolved oxygen was found to dramatically influence the intensity of flashlamp-pumped organic-dye lasers. The relative energy per laser pulse was measured for nine new and 19 previously reported dye solutions in equilibrium with partial pressures of oxygen ranging from 0 to 1 atmosphere.

Observations of the morphology of laser-induced damage in copper mirrors

The results of multiple‐pulse damage tests on copper mirrors using 1.7‐ns CO2 lasers are reported. The measured reduction in the brightness reflectivity of the mirrors is shown to be correlated to the dramatic appearance of fine scale microstructure on the mirror surface. Scanning electron micrographs of this surface structure are presented and possible explanations of the effects are discussed.

Observation of amplified reflection through degenerate fourwave mixing at CO(2) laser wavelengths in germanium.

We report the first known observation of amplified reflection through degenerate four-wave mixing at 10.6 microm. Reflectivities of over 100% are reported in both n-type and p-type germanium at pump intensities of about 100 MW/cm(2). The maximum reflectivity reported is 800% in p-type Ge.

Application of a phase-conjugate Brillouin mirror to generation of high-quality variable-duration KrF pulses

Phase conjugation by Brillouin scattering in SF/sub 6/ gas has been implemented on a two-pass KrF amplifier to provide near-diffraction-limited output pulses having a very low background level of amplified spontaneous emission. The pulse duration is variable between 1 and 10 ns by simply attenuating the input pulse. These pulses have also been used for the generation of much shorter duration pulses by truncated Brillouin scattering at the surface of cyclohexane. >

Observation of resonantly enhanced degenerate four-wave mixing in doped alkali halides

We describe the first reported observation of resonantly enhanced phase conjugation through degenerate four-wave mixing (DFWM) in doped alkali halides. We also describe the first reported quantitative comparison of the resonant DFWM process in the infrared with the theory of Abrams and Lind [Opt. Lett. 2, 94 (1978); 3, 205 (1978)]. The comparison for small values of alpha0L is shown to be excellent. For alpha0L in excess of 3, experiment and theory diverge because of pump attenuation by the resonant medium.

Plasma-breakdown retropulse isolators for the infrared

The design and performance of a passive plasma isolator for suppressing retropulses in high-power CO(2) laser-fusion systems are described. The device uses a gas-filled spatial filter designed to produce a plasma at the focal plane iris. General design criteria for these isolators are discussed, and the performance of a specific isolator is evaluated. For the unit tested, retropulse attenuations of 33 dB for focal plane intensities of 1.5 TW/cm(2) have been demonstrated.

Determination of the third-order nonlinear optical coefficients of germanium through ellipse rotation

We describe the first reported direct determination of the 10 -Am nonlinear susceptibility in intrinsic Ge through time-resolved ellipse rotation. We found that X(3)(1111). = 2.5 X 10(-11) esu and X(3)(1221)= 1.3 X 10(-11) esu, significantly below previous estimates.

Amplification of multiline/multiband CO2 laser pulses

Amplification measurements of single‐line and multiline/multiband nanosecond CO2 laser pulses are reported. It is shown that at amplifier pressures of 600 Torr the saturation energy for multiline pulses is twice as large as for single‐line pulses.

A new saturable absorber for the CO2 laser using doped KCl

A new class of saturable absorbers for 10‐μm applications using doped alkali halides is demonstrated. For the ReO−4 molecular ion in KCl, the vibrational transition saturates like an ideal two‐level system. This behavior is a result of the large anharmonic shift in the absorption spectra of the dopant ion. Saturation parameters of 1.45 MW/cm2 and a relaxation time T1 of 120 ps are measured at room temperature.