13 May 1997 Laser intensity modulation by nonabsorbing defects
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Nonabsorbing defects can lead to laser damage. Defects such as voids, microcracks and localized stressed concentrations, even if they differ from the surrounding medium only be refractive index, can serve as positive or negative lenses of 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 wave number 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 as well as linear and planar microlens can all have strong effects. The present paper evaluates the intensification due to spherical voids and high refractive index inclusions.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Michael D. Feit, Alexander M. Rubenchik, "Laser intensity modulation by nonabsorbing defects", Proc. SPIE 2966, Laser-Induced Damage in Optical Materials: 1996, (13 May 1997); doi: 10.1117/12.274235; https://doi.org/10.1117/12.274235

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