J. Goldhar

Raman pulse compression of excimer lasers for application to laser fusion

Application of efficient ultraviolet excimer lasers such as the 248 nm KrF laser to laser fusion requires that long laser pulses be efficiently converted to short pulses at high intensity. The backward Raman amplifier is shown to be a promising candidate for this application. Gain, saturation, and limits to amplifier performance are described. It is shown that pump beams of poor spatial quality may be converted to output beams of high spatial quality. Several common gaseous vibrational Raman scatterers are discussed, and it is shown that a simple KrF-pumped backward Raman amplifier using methane at atmospheric pressure will have a saturation fluence near 1 J/cm2and can produce an output five times as intense as the pump in a ten times shorter pulse with an efficiency of about 50 percent. Design tradeoffs and possible techniques for further improving the performance of such amplifiers are discussed.

An injection-locked unstable resonator rare-gas halide discharge laser of narrow linewidth and high spatial quality

An oscillator-amplifier KrF discharge laser system capable of providing up to 400 mJ output with 0.1-cm-1linewidth in a 20-ns pulse is described. The output beam divergence is described and shown to be affected by the discharge current. The output beam is near the diffraction limit in the direction parallel to the discharge and about three times the diffraction limit transverse to the discharge. Operation with XeCl at up to 250 mJ with similar linewidth and spatial quality is also described.

Injection locking of a xenon fluoride laser

Operation of a XeF laser at high spectral power densities on transitions within a single vibrational band has been demonstrated. An electron‐beam‐controlled discharge XeF laser was operated as an injection‐locked regenerative amplifier. A narrow‐band signal from an etalon‐tuned XeF laser was used to lock the regenerative amplifier. Competition between the various components of the emission spectrum was observed. Homogeneous extraction is observed within each vibrational band, indicating that the rotational cross‐relaxation time is substantially faster than the radiative lifetime of XeF. Coupling between vibrational bands was not observed. These measurements indicate that the efficient extraction from XeF on a single rotational transition should be possible. The band at 351 nm was found to consist of components arising from at least two different vibrational bands. The transitions in the 353‐nm band and one component of the 351‐nm band share a common vibrational level in the upper electronic state. These o...

Backward Raman gain measurements for KrF laser radiation scattered by CH4

Backward Raman small‐signal gain measurements for a KrF laser scattered by methane gas, including linewidth and pressure dependences, are presented. A 268‐nm probe beam is produced from a 249‐nm pump beam by superfluorescent emission in a methane cell, and is amplified by a counterpropagating KrF beam at 249 nm in a second methane cell. The results are consistent with theoretical predictions for the backward Raman amplifier.

An efficient double-pass Raman amplifier with pump intensity averaging in a light guide

Experimental observations on a double-pass methane Raman amplifier pumped by a KrF laser demonstrate efficient photon extraction (75-85 percent) of multiple pump pulses and high stage gain (10-20) with simultaneous intensity gain or pulse compression of about 2. The Stokes beam divergence is about 2.5 times the diffraction limit and is unchanged in the amplifier to within the precision of the experiment. The pump pulses are of poor spatial quality and propagate through the amplifier in a light guide. A simple one-dimensional theoretical model fits the results of the experiment. Analysis using the model permits a projection of the performance of very large final Raman amplifier-compressor stages for fusion laser systems. These systems, with somewhat better controlled pulse shapes than those used in the experiment, can deliver average intensity gains of 2-3 at a net energy conversion efficiency (all losses included) of about two thirds and a stage gain of 30.

Large‐signal gain and intensity enhancement in a backward Raman amplifier

Saturation effects have been investigated in a KrF laser‐pumped backward Raman amplifier using methane gas. Pump depletion of 30% with an intensity gain of 2 has been demonstrated, and the results are shown to be consistent with a simple Frantz‐Nodvik saturation treatment.

High‐efficiency energy extraction in backward‐wave Raman scattering

Pump depletions of 70–75% have been demonstrated for a KrF‐laser‐driven, methane‐gas‐filled backward Raman amplifier and are in agreement with predictions of the Frantz‐Nodvik saturated‐amplifier model. The associated counterpropagating Stokes laser intensity is determined to be ≳3.5 times that of the pump; the corresponding pulse compression ratio is ≈5.

Dylux: an instant image photographic material suitable for UV laser beam diagnostics

Dylux-a DuPont Corp. Photo Products Department instant image dry process photographic proofing material developed for the graphic arts industry has been found useful UV laser beam diagnostics and quantitative beam profile measurements. (AIP)

Beam deflecting optical switch using volumetric thermal gratings.

Volumetric thermal gratings were created in liquid and gaseous media and were used to efficiently deflect laser beams. In gaseous media, a low-input energy requirement and high switching efficiency make this type of switch a good candidate for a practical device. The switch is scalable to large apertures and has low insertion loss.

Pulse compression by pulse-stacking in a KrF amplifier

A laser pulse-compression technique employed to obtain intense pulses (~1 GW) from an electron-beampumped KrF amplifier is demonstrated. This technique consists of time-sequencing and angle-coding separate pulses through the amplifier. The system described uses four pulses for a nominal temporal compression factor of 4. The input vs output temporal pulse shapes and saturation characteristics are demonstrated. Also discussed are the issues of parasitic oscillations, optical cross talk, saturation pulse broadening, and limitations on scaling to larger compression factors.