Irving Liberman

The Spherical Reflector for Use in the Optical Pumping of Lasers

The coupling of optical energy from a lamp into a laser rod using a spherical mirror enclosure has been analyzed using geometrical optics. The calculations indicate that about 75% coupling can be obtained for typical sized laser rods and spheres. Experimental results for a 3 mm x 30 mm Nd: Cr: YAG rod are given. Using external resonators, a slope efficiency of 1.15% and an output power of 3.4 W were observed for an input power of 870 W.

A High Resolution Rapid-Scanning Spectrometer

A Czerny-Turner type spectrometer has been designed and operated as a rapid scanning instrument by placing a rotating mirror near the exit slit. Using a helium-neon gas laser, resolution of 0.027 A has been measured at scanning rates of 0.4 A/microsec. Data have been taken with the scanning rate of 6 A/microsec, which could have been increased an order of magnitude if desired. A scanning range of 1-600 A depending on the grating and mirrors used has been obtained. Applications shown included the shift and shape of xenon spectral lines in a pulsed arc discharge. The associated electronics required for synchronization are included.

A Comparison of Lamps for Use in High Continuous Power Nd:YAG Lasers

The efficiency of krypton, xenon, and tungsten-iodine lamps for pumping Nd: YAG are compared both spectroscopically and by laser pumping. The relative pumping efficiencies of xenon and tungsten to krypton are 0.86 and 1.1, respectively. However, because the tungsten filament uses a higher percentage of its power in overcoming the laser threshold, the krypton lamp with its larger power density yielded the best over-all efficiency. An output power of 105 W was obtained at an input power of 3610 W for an over-all efficiency of 2.9%.

Optical analysis of laser systems using interferometry

Previous methods of predicting focal spot parameters such as the Strehl ratio and encircled energy of large laser systems like the Los Alamos fusion CO(2) lasers involved the digitization of interference patterns of the optical components and propagation of the complex amplitude and phase of the wave front throughout the system. In the new approach described in this paper, the computational procedure has been extended to produce computer plots of the final emerging wave front. This enables direct comparison with the experimentally produced wave front of the total system and opens the way for optical analysis, design, and possible optimization of laser systems, especially CO(2) laser systems. The computational procedure and the Twyman-Green and Smartt IR interferometers constructed to verify this approach are described. The implications of the results are discussed.

Efficient cavity-dumped HgBr laser.

The technique of cavity dumping was used to generate 8-nsec (FWHM) laser pulses from an UV preionized discharge-pumped HgBr laser emitting at 502 nm. The pulse width corresponds to the photon round trip transit time of the resonator. Optical output energies of 11.5 mJ/pulse and cavity-dumping efficiencies of 58% were obtained with a KD*P Pockels cell and thin-film multilayer-dielectric polarizer. Short-pulse blue-green laser radiation is useful for bathymetry and other underseas ranging applications.

Laboratory simulation of highly radiative plasmas

Abstract Highly radiative plasmas, in which the radiative transport within the plasma is a dominant factor, can be simulated within the laboratory using a wall-stabilized pulsed arc discharge. By varying the initial pressure and peak power input, the plasma can be changed from optically thin over the major portion of the spectral emission to nearly black body-like. We have in progress an experimental and theoretical investigation of these radiative plasmas in xenon to study radiative and thermal energy transport within the arc and that transferred to the surroundings. The theoretical approach included investigations towards solving the energy balance equation (neglecting convective heat transport) for a non-homogeneous temperature plasma of widely varying opacity. This paper will discuss primarily the experimental techniques involved in this study of relatively long duration (∼1 msec) pulsed arcs. Measurements of the radial distribution of the spectral radiance of the continuum in the ultraviolet, where the plasma should be optically thin, indicate the temperature distribution. Similar measurements in the vicinity of the strong emission lines or the continuum in the infrared enable the temperature in the arc to be determined.

Bathymetry CuBr laser.

The design and performance of a short-pulse high-repetition-rate CuBr laser suitable for bathymetry is described. The pulse width and peak power were 4.5 nsec and 30 kW, respectively, corresponding to 140 microJ/pulse. These conditions occurred at a repetition rate of 16 kHz and an overall efficiency of 0.14% within a compact long-lived sealed-off discharge.

Automatic target alignment of the Helios laser system

An automatic target-alignment technique for the Helios laser facility is reported and verified experimentally. The desired alignment condition is completely described by an autocollimation test. A computer program examines the autocollimated return pattern from the surrogate target and correctly describes any changes required in mirror orientation to yield optimum target alignment with either aberrated or misaligned beams. Automated on-line target alignment is thus shown to be feasible.