Femtosecond filamentation in transparent media

Self-focusing: Theory

Results of laser‐induced breakdown experiments in fused silica (SiO2) employing 150 fs–7 ns, 780 nm laser pulses are reported. The avalanche ionization mechanism is found to dominate over the entire pulse‐width range. Fluence breakdown threshold does not follow the scaling of Fth∼ √τp, when pulses are shorter than 10 ps. The impact ionization coefficient of SiO2 is measured up to ∼3×108 V/cm. The relative role of photoionization in breakdown for ultrashort pulses is discussed.

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Laser‐induced breakdown by impact ionization in SiO2 with pulse widths from 7 ns to 150 fs

Nonlinear Optical Crystals: A Complete Survey

A review is given of recent experimental results on laser-induced electric breakdown in transparent optical solid materials. A fundamental breakdown threshold exists characteristic for each material. The threshold is determined by the same physical process as dc breakdown, namely, avalanche ionization. The dependence of the threshold on laser pulse duration and frequency is consistent with this process. The implication of this breakdown mechanism for laser bulk and surface damage to optical components is discussed. It also determines physical properties of self-focused filaments.

Laser-induced electric breakdown in solids

An extensive review of theoretical and experimental investigations conducted over the last two decades since the advent of the laser and relating to the simultaneous absorption of one or more photons by the valence electrons of a crystalline solid is given. The following topics are addressed, with greatest emphasis on the most recent results: the pioneering models of Braunstein and Ockman and that of Basov for two-photon absorption in direct-gap crystals, based on second-order time-dependent perturbation theory and parabolic and isotropic energy bands; extensions and modifications of the above models by various authors to take into account the effects of excitons, crystal anisotropy, laser polarization, and nonparabolicity as well as degeneracy of the electronic energy bands; rigorous band-structure calculations that employ realistic energy bands and momentum matrix elements that include many intermediate states to obtain good convergence in the perturbation calculation; the semiclassical theory of Keldysh that takes into account electric-field effects on the electronic energies and wave functions and that employs first-order perturbation theory to obtain multiphoton transitions of all orders; the fully quantized treatment of the multiphoton absorption (MPA) process along the above lines by Kovarskii and Perlin; the Volkov approximation method of Jones and Reiss; descriptions of the various experimental techniques that are usually employed to study nonlinear phenomena in solids; critical comparison between different theoretical predictions and experimental data; and finally, theoretical and experimental work relating to phonon-assisted two-photon transitions, three-photon absorption, four-photon absorption, and higher-order MPA processes in crystalline solids.

Review of multiphoton absorption in crystalline solids

In the application of high-power lasers, damage to active laser materials, and to components of laser system, generally determines the limit of useful laser performance. Accordingly, there is great interest in reducing the susceptibility of optical elements ot damage. Damage in transparent dielectrics arises from three major causes, particulate inclusions or microinhomogeneities in the material, self-focusing within the materials, and surface damage due to plasma formation. The state of understanding of these phenomena, and the thresholds observed, where they have been determined, will be discussed. Dependence on pulse length will also be considered. Although most of the research accomplished to date on laser damage has concentrated on Nd-glass, the advent of very high-powered gas lasers has stimulated interest in the development of damage resistant component materials for use in the ir. Crystalline dielectrics appear to be the most likely candidate materials for ir windows. Nonlinear optics materials are particularly susceptible to damage, since they are generally exposed to high intensity radiation. Asa final item, damage in thin film dielectric coatings are considered.

Laser Induced Damage of Optical Elements-a Status Report.

The third ASTM symposium on damage in laser materials held at NBS in May 1971 is discussed, and the results are reviewed.

Damage in laser materials.

The role of thermal conductivity in the pulsed laser damage sensitivity of optical thin films

A number of commercially available optical coatings, both antireflective and high reflective, have been tested for their laser-induced damage threshold, involving a total of eight different laboratories. The results obtained and the experimental methods used at these laboratories were discussed among the participants in this round robin at a minisymposium held at Balzers, Liechtenstein, 9–10 Dec. 1982. A final report of the round robin and a summary of the conclusions drawn at that symposium are presented.

Arthur H. Guenther

Papers

Review of multiphoton absorption in crystalline solids

Laser Induced Damage of Optical Elements-a Status Report.

Damage in laser materials.

The role of thermal conductivity in the pulsed laser damage sensitivity of optical thin films

1.06 Micron Laser Damage of Thin Film Optical Coatings — a Round Robin Experiment Involving Various Pulse Lengths and Beam Diameters