Z-scan theoretical and experimental studies for accurate measurements of the nonlinear refractive index and absorption of optical glasses near damage threshold

Thomas Olivier; Franck Billard; Hassan Akhouayri

doi:10.1117/12.524854

10 June 2004 Z-scan theoretical and experimental studies for accurate measurements of the nonlinear refractive index and absorption of optical glasses near damage threshold

Thomas Olivier, Franck Billard, Hassan Akhouayri

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Proceedings Volume 5273, Laser-Induced Damage in Optical Materials: 2003; (2004) https://doi.org/10.1117/12.524854
Event: XXXV Annual Symposium on Optical Materials for High Power Lasers: Boulder Damage Symposium, 2003, Boulder, Colorado, United States

Abstract

Self-focusing is one of the dramatic phenomena that may occur during the propagation of a high power laser beam in a nonlinear material. This phenomenon leads to a degradation of the wave front and may also lead to a photoinduced damage of the material. Realistic simulations of the propagation of high power laser beams require an accurate knowledge of the nonlinear refractive index γ. In the particular case of fused silica and in the nanosecond regime, it seems that electronic mechanisms as well as electrostriction and thermal effects can lead to a significant refractive index variation. Compared to the different methods used to measure this parmeter, the Z-scan method is simple, offers a good sensitivity and may give absolute measurements if the incident beam is accurately studied. However, this method requires a very good knowledge of the incident beam and of its propagation inside a nonlinear sample. We used a split-step propagation algorithm to simlate Z-scan curves for arbitrary beam shape, sample thickness and nonlinear phase shift. According to our simulations and a rigorous analysis of the Z-scan measured signal, it appears that some abusive approximations lead to very important errors. Thus, by reducing possible errors on the interpretation of Z-scan experimental studies, we performed accurate measurements of the nonlinear refractive index of fused silica that show the significant contribution of nanosecond mechanisms.

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Thomas Olivier, Franck Billard, and Hassan Akhouayri "Z-scan theoretical and experimental studies for accurate measurements of the nonlinear refractive index and absorption of optical glasses near damage threshold", Proc. SPIE 5273, Laser-Induced Damage in Optical Materials: 2003, (10 June 2004); https://doi.org/10.1117/12.524854

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KEYWORDS

Refractive index

Transmittance

Silica

Gaussian beams

Absorption

Beam propagation method

Optical simulations

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