Laser intensity modulation by nonabsorbing defects

Michael D. Feit; Alexander M. Rubenchik

doi:10.1117/12.294285

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8 December 1997 Laser intensity modulation by nonabsorbing defects

Michael D. Feit, Alexander M. Rubenchik

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Proceedings Volume 3047, Solid State Lasers for Application to Inertial Confinement Fusion: Second Annual International Conference; (1997) https://doi.org/10.1117/12.294285
Event: Second International Conference on Solid State Lasers for Application to ICF, 1996, Paris, France

Abstract

Nonabsorbing bulk defects can initiate laser damage in transparent materials. Defects such as voids, microcracks and localized stress concentrations can serve as positive or negative lenses for the incident laser light. The resulting interference pattern between refracted and diffracted light can result in intensity increases on the order of a factor of 2 some distance away from a typical negative microlens, and even larger for a positive microlens. Thus, the initial damage site can be physically removed from the defect which initiates damage. The parameter that determines the strength of such lensing is (Ka)² (Delta) (epsilon) where the wavenumber K is 2(pi) /(lambda) , 2a is the linear size of the defect and (Delta) (epsilon) is the difference in dielectric coefficient between matrix and scatterer. Thus, even a small change in refractive index results in a significant effect for a defect large compared to a wavelength. Geometry is also important. 3D (eg. voids) as well as linear and planar (eg. cracks) microlenses can all have strong effects. The present paper evaluates the intensification due to spherical voids and high refractive index inclusions. We wish to particularly draw attention to the very large intensification that can occur at inclusions.

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Michael D. Feit and Alexander M. Rubenchik "Laser intensity modulation by nonabsorbing defects", Proc. SPIE 3047, Solid State Lasers for Application to Inertial Confinement Fusion: Second Annual International Conference, (8 December 1997); https://doi.org/10.1117/12.294285

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