Few-cycle pulses for bulk micromachining of fused silica

摘要

Laser pulse duration is a factor of paramount importance when considering direct laser bulk microprocessing of transparent materials in tight focusing conditions. Regardless of the chemical composition of the substrate, the existence of two laser-matter interaction types (Type I and Type II) is firmly established. In fused silica, Type I modifications can only be obtained when using pulse durations below 180 fs and modest pulse energies (0.1 to 0.2 μJ). The shorter the pulse duration, the wider the processing window. For instance, microprocessing with a 40-fs pulse duration results in Type I modifications for pulse energies up to 0.4 μJ. In this proceeding, we report on using few-cycle pulses to induce microstructures in the volume of fused silica samples. Few-cycle pulses are characterized by a broad spectrum which prohibits using conventional refractive optics. Therefore, a gold-coated reflective objective confines the electromagnetic radiation into the sample. We examine the influence of the irradiation conditions (pulse energy, number of pulses) on the characteristics of the laser-induced microstructures. The characterization of the photoinduced microstructures (morphology, refractive index change) is performed with a conventional phase-contrast microscope. As a consequence of the spatio-temporal modulation of the beam profile upon aberrations, varying the depth of focus results in producing Type I and Type II structures alternatively.