F. J. McClung

Giant Optical Pulsations from Ruby

Giant pulses of optical maser radiation have been produced which are several orders of magnitude larger than the commonly observed spontaneous pulses. The pulses were produced by varying the effective reflectivity of the reflecting surfaces at the ends of the ruby rod through a Kerr‐cell switching technique. The measured pulse characteristics are found to be in agreement with theoretical predictions.

HOLOGRAM RECORDING ON PHOTOPOLYMER MATERIALS

A photosensitive material based on photo‐induced polymerization has been used to record holograms. Exposure of 1 to 30 mJ/cm2 at 0.694 μ were followed by rapid optical, dry processing with ultraviolet radiation. Good resolution and diffraction efficiencies of up to 45% into the first order were observed.

8A2 - The self-focusing of light of different polarizations

In an effort to verify the hypothesis that molecular reorientation (ac Kerr effect) is responsible for the self-focusing of light beams in certain liquids, we have measured and compared the thresholds and other characteristics of self-focusing for circularly and linearly polarized beams incident on these liquids. We show that for plane waves propagating in a homogeneous, isotropic, ensemble of molecules having anisotropic polarizability tensors, the nonlinear index should be four times as great for linearly as for circularly polarized waves. The hope that this difference in indexes would be reflected in a four-fold increase in the threshold power for self-trapping when circularly instead of linearly polarized light is incident was not realized. In practice, the increase was always found to be much less. However, in every case studied, the trapped light from a beam, circularly polarized to better than 1 part in 200, was markedly, if not completely, depolarized as soon as self-trapping could be detected. We show qualitatively that this polarization instability should exist for all but linearly polarized light and for a variety of nonlinear mechanisms. However, in the absence of even an approximate quantitative theory of the self-trapping of light that is not linearly polarized, the comparative measurements of thresholds cannot be said either to verify or disprove the hypothesis of molecular reorientation.

Longitudinal mode control in giant pulse lasers

We have introduced longitudinal mode selection into a giant pulse laser to obtain single mode output from the laser. Some advantages of achieving longitudinal mode control in a giant pulse laser are noted. The methods of mode control used are described. These include orienting various reflecting surfaces in the laser cavity, cooling the ruby laser crystal, and introduction of a saturable dye in the cavity. Methods of measuring the mode structure are given. Results of these measurements with varying degrees of mode control are described in detail. Under some conditions it is possible to obtain essentially single mode behavior from the giant pulse laser.

R2 Line Optical Maser Action in Ruby

Optical maser action at the R2 line in ruby has been observed. Because of a fast thermal relaxation between the two 2E levels, it is not usually possible to satisfy the maser conditions at the R2 line when stimulated emission is occurring at the R1 line. However, if maser action can be suppressed at the R1 line, even at high inversion, it can be made to occur at the R2 line by the appropriate selection of operating conditions. This has been accomplished by using, for end reflectors, multilayer dielectric interference filters which have high transmission at the R1 line and low transmission at the R2 line. The selection of the operating conditions requires a correction of the absorption coefficients for the R1 and R2 lines based on the Boltzmann distribution between the two excited states. When the Boltzmann correction is made, the calculations show reasonable requirements on pumping threshold and reflectivities.

Comparison of Observed and Predicted Stimulated Raman Scattering Conversion Efficiencies

We have measured the absolute Raman scattering cross section for the 1345‐cm−1 shifted Stokes line in nitrobenzene using a ruby laser. We have also measured the efficiency of conversion of radiation from a giant pulse ruby laser into stimulated Raman scattered radiation for this line. We have found that the average intensity needed to produce a given conversion is one or two orders of magnitude less than that predicted by the theory of Hellwarth using our measured cross section. We discuss some possible explanations for this disagreement.

Some Experiments Performed with a Reflected-Light Pulsed-Laser Holography System

A short-exposure, high-energy holography system has been constructed which yields high quality holograms of scenes several cubic meters in volume. The system is constructed around a single mode Q-switched ruby oscillator and a 20-dB gain single-pass ruby amplifier. The output is fully coherent at peak output of 10 J. Front lit holograms of transient events and of live subjects have been made with this system.

Operation of a Transverse Mode‐Controlled Hydrogen Stokes Laser Oscillator

A giant pulse ruby laser was used to optically pump a hydrogen gas laser oscillator, operating at the first Stokes‐shifted Raman line at 0.975 μ. Transverse mode control of the high‐Q, curved mirror resonator was provided by controlling the geometry of the pump beam; this allowed operation in the fundamental (TEM00) mode of the cavity. Operating characteristics, including threshold, beam divergence, and spatial and temporal behavior, are discussed.