Abstract
In this contribution we experimentally demonstrated femtosecond laser micro-processing of large arbitrary-shaped irradiance patterns in silicon without sample or beam scanning. This is mainly accomplished by carrying out spatial and temporal shaping of femtosecond pulses with the help of a phase-only spatial light modulator (SLM, PLUTO-NIR-II), and an acousto-optic programmable dispersive filter (Dazzler from FASTLITE). In particular, the spectral phase of the femtosecond pulse is changed by introducing different sets of dispersion parameters into the Dazzler, whereas the amplitude and spatial phase of the laser beam is controlled with a single phase mask encoded into the SLM. Each phase mask is designed following a specific method for encoding complex fields into a single phase element [1]. By using this diffraction-based method one can produce user-defined spatially uniform irradiance patterns with different spatial shapes at the surface of the silicon sample. Here, it should be mentioned that a suited setting of the position of the surface of the silicon sample with respect to the ablation plane is carried out by means of a multi-axis motorized stage (denoted by MS in Fig. 1). Before starting the micro-processing, the adequate laser fluence must be also determined. Then, in a single-shot regime controlled with a motorized shutter, the ablation process due to the interaction of above-mentioned irradiance patterns with the material surface is accomplished. Note that, under laser fluence range lower than 1 J/cm2 the dominate ablation mechanisms of spallation and fragmentation in metals [2] occur with minimal thermal or mechanical damages in the surrounding of the processed area. In addition, the lack of sequentially dot-by-dot scans over a sample considerably reduces the fabrication time and avoids boundary effects due to the ablation craters overlap.
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