M. Bass

CZOCHRALSKI GROWTH AND PROPERTIES OF YAlO3 LASER CRYSTALS

Czochralski growth characteristics of a new laser host crystal, YAlO3, and measurements of its optical, thermal, and mechanical properties are reported. Stimulated emission from Nd3+ in YAlO3 has been observed.

Avalanche breakdown and the probabilistic nature of laser-induced damage

This paper discusses the probabilistic nature of the damaging interaction between light and matter. It is shown that when one recognizes that there is some probability to induce damage at any level of optical irradiation, then the reported irreproducible damage-resistance properties of many useful materials can be understood. This point of view also explains why some optical components may be safely irradiated many times before damage occurs, though no other change in the material can be detected prior to the observation of damage. Experimental data showing the probability for surface damage as a function of power density are presented for several materials. The dependence of damage probability on optical field strength is similar to that of the dc ionization coefficients for semiconductors and gases on the applied field. This observation is discussed and it is suggested that a form of avalanche breakdown might be the cause of laser-induced damage.

Confirmation of an Electron Avalanche Causing Laser-induced Bulk Damage at 1.06 μm

Measurements have been made on intrinsic optical bulk breakdown in ten alkali halides at 1.06 microm and in one at 0.69 microm. By comparing the results to previously reported experiments conducted at 10.6 microm and at direct current, it has been possible to identify the damage mechanism as electron avalanche breakdown. Self-focusing has been controlled by restricting the probe powers to well below the critical powers for catastrophic self-focusing, and damage from inclusions has been distinguished from intrinsic damage. Implications of this work for surface damage studies are explored.

Laser-Induced Damage Probability at 1.06 μm and 0.69 μm

The first directly comparable measurements of the laser-induced surface damage process at both ruby and Nd:YAG laser wavelengths are reported. The most striking feature of the data is that all the materials studied are harder to damage at 0.69 microm than at 1.06 microm. The probabilistic nature of the laser-induced damage process at 1.06 microm was explored further by measuring the distribution of breakdown starting times with an image-converter streak camera. The observed distribution is described by the compound probability that breakdown occurs at a particular time, given that it has not occurred before that time. In addition, several connections between the probabilistic and thresholdlike interpretations of laser-induced damage are discussed. It is shown that these points of view are not totally incompatible.

Nd,Cr : YAlO3 LASER TAILORED FOR HIGH‐ENERGY Q‐SWITCHED OPERATION

Spectral and pulsed laser properties of Nd3+ : YAlO3 crystals codopes with Cr3+ are described. The anisotropic properties of yttrium orthoaluminate were used to select a laser rod orientation which maximized the energy storage capability for Q‐switched operation. It is demonstrated that a c‐axis rod of this material can produce energy outputs greater than those obtainable from the best Nd3+ : YAG rods of comparable size in both long‐pulse and Q‐switched laser operation.

Laser Action and Spectroscopic Properties of Er3+ in YAlO3

Stimulated emission at 1.663 μ due to a 4S3/2→4I9/2 transition has been observed from Er3+ ions in a crystal of YAlO3. The threshold for pulsed laser action at room temperature was 52 J. Crystalline Stark levels determined from absorption and fluorescence spectra and fluorescence lifetimes of YAlO3:Er3+ are reported.

OPTICAL SECOND‐HARMONIC GENERATION IN CRYSTALS OF ORGANIC DYES

Optical second‐harmonic generation has been observed in crystals of six organic dyes. One dye, 7‐diethylamino‐4‐methylcoumarin, appears to be at least as good a frequency doubler as LiNbO3 and has a much higher resistance to surface damage.

wavelength dependent time development of the intensity of dye solution lasers

It has been observed that the intensity of laser emission from two different dye solution lasers (DTTC in DMSO and cryptocyanine in glycerol) reaches a maximum at the shortest wavelength in the emission band before it peaks at the longest. A simple model of dye solution lasers which explains this wavelength-time effect is presented. This effect can be interpreted to yield information on the rate of relaxation of internal energy of the dye molecule. The evidence suggests that, on the time scale of the laser action in these experiments (∼20 ns) the ground state of the dye molecule is inhomogeneously broadened. In addition, it is shown that certain other of the dye lasers properties may be understood by analysis of the solutions absorption and fluorescence spectra.

BROAD‐BAND LIGHT AMPLIFICATION IN ORGANIC DYES

Two organic dyes previously used as liquid lasers, DTTC and cryptocyanine, have been used as broad‐band (>300 A) pulsed light amplifiers in the 7000–8500 A range. If the input frequency is close to the frequencies of the usual laser oscillations, the latter are quenched and the energy transferred to the frequency being amplified.

Comparison of laser‐induced surface and bulk damage

Data are presented which show that the optical field required to produce damage on a conventionally polished surface of a transparent medium is less than that required to damage an imperfection‐free surface. Electric field enhancement at imperfections can explain this result. In addition, the bulk damage field at 1.06 μm is reported for three materials and is found to be the same as the surface damage field on imperfection‐free surfaces.Data are presented which show that the optical field required to produce damage on a conventionally polished surface of a transparent medium is less than that required to damage an imperfection‐free surface. Electric field enhancement at imperfections can explain this result. In addition, the bulk damage field at 1.06 μm is reported for three materials and is found to be the same as the surface damage field on imperfection‐free surfaces.