Showing papers by "Arkadi Rosenfeld published in 1999"

Ultrashort-laser-pulse damage threshold of transparent materials and the role of incubation

Abstract: We present investigations of the surface damage threshold for transparent materials, e.g. a-SiO2, CaF2 and LiF, after single- and multiple-laser-pulse irradiation at 800 nm in the picosecond and sub-picosecond duration range. Our study shows clearly that the surface damage threshold drops dramatically during multiple-laser-shot irradiation, due to material-dependent incubation effects. This has important consequences for applications such as laser machining and for the lifetime of optical components. Different processes that can reduce the surface damage threshold with increasing laser shots are evaluated, such as sub-surface damage and defect formation. The mechanism of laser-induced defect formation, e.g. color centers, is believed to be mainly responsible for the observed reduction in the threshold for surface damage with increasing laser-shot numbers.

Material processing of dielectrics with femtosecond lasers

Abstract: Ultrashort laser pulses have considerable potential for micron and sub-micron structuring of several materials. The lower energy impact, the reduction of thermal damage, the elimination of laser-plume interaction, and the exploitation of nonlinear optical effects all contribute to a strong improvement when compared to results using pulse widths in the nanosecond range. Depending on the choice of fluence compared to the damage threshold, with ultra-short laser pulses one is able to generate different types of structures, minimizing the heat affected zone. The damage threshold drops dramatically during the first laser shots, due to defect incubation. This has important consequences for applications, such as laser machining and for the lifetime of optical components. At a fluence below surface damage threshold we were also able to generate bulk modifications of different size and location in a controllable fashion by variation of laser pulse width, energy and number of shots, utilizing the beam narrowing effects during self focusing. A study of the dependence of the structure depth on the square root of the laser power for a given pulse length provides a straightforward method for determining the non-linear index of refraction.

Morphological and mechanical investigations of bariumalumoborosilicate glass surfaces processed with 700-fs laser pulses

Abstract: We present surface micro-modifications of bariumalumoborosilicate glasses with a high transformation temperature near 700 °C. Laser processing of the glass substrate was realized by using ultra-short laser pulses at 800 nm. The morphological conversion of the laser-treated surfaces was characterized by scanning force microscopy and nano-indentation. A hardness increase by at least a factor of six on the laser ablation crater edge relative to illuminated non- ablated areas shows that the material in the crater walls underwent drastic morphological and mechanical changes. In this heat- and shock-affected zone, the material became more elastic as a result of increased stress.

Non-thermal and thermal processes in the ultra-short laser ablation of sapphire

Abstract: Summary form only given. The purpose of this study is to distinguish between non-thermal and thermal processes that lead to laser ablation of wide band-gap dielectrics (in our case sapphire) under ultrashort (sub-ps and ps) infrared laser pulse irradiation. Two ablation phases, a gentle-etch phase and a strong-etch phase, have been distinguished in the process of laser sputtering as a function of pulse duration, laser fluence and number of pulses, which are regarded as the key parameters that govern the laser-induced ablation process. We focus our attention on the non-thermal processes directly related to particle emission, as a consequence of the electronic processes that initiate and mediate the laser interaction.

Surface damage threshold and structuring of brittle dielectrics with ultra-short laser pulses

Abstract: Summary form only given. Ultra-short pulse laser systems provide the possibility for accurate structuring of wide band-gap materials such as transparent dielectrics. In this work we illustrate the problem of laser induced micro-patterning on crystalline LiYF/sub 4/ (YLF).