Nonlinear photoionization and laser-induced damage in silicate glasses by infrared ultrashort laser pulses |
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Authors: | L A Siiman J Lumeau and L B Glebov |
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Institution: | (1) College of Optics & Photonics: CREOL & FPCE, Univ. of Central Florida, P.O. Box 162700, Orlando, FL 32816-2700, USA |
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Abstract: | We show that photoionization of wide band gap silicate glasses by infrared ultrashort laser pulses can occur without laser-induced
damage. Two glasses are studied, fused silica and a multi-component silicate photo-thermo-refractive (PTR) glass. Experiments
are performed by low numerical aperture focusing of ultrashort laser pulses (100 fsec<τ<1.5 psec) at the wavelengths 780 nm, 1430 nm, and 1550 nm. Filaments form inside both glasses and are visibly observable
due to intrinsic luminescence. Keldysh’s theory of nonlinear photoionization is used to model the formation of filaments and
values of about 1013 W cm−2 for the laser intensity and 1019 cm−3 for the free electron density are estimated for stable filaments to arise. Laser-induced damage is studied by the generation
of a third harmonic from an interface created between a damage site and the surrounding glass matrix. It is found that third
harmonic generation occurs only after several thousands of laser shots indicating that damage is not a single-shot phenomena.
The ability to photoionize PTR glass without damage by ultrashort laser pulses offers a new approach for fabricating diffractive
optical elements in photosensitive glass. |
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Keywords: | PACS" target="_blank">PACS 52 38 Hb 42 50 Hz 42 70 Ce 79 20 Ds |
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