Generation of extremely high-angle Bessel beams.

We present a setup to generate tightly focused Bessel beams that is composed of a half-ball lens coupled with a relay lens. The system is simple and compact compared to conventional imaging of axicons based on microscope objectives. We experimentally demonstrate the generation of a Bessel beam with a 42° cone angle at 980 nm in air with a typical beam length of 500µm and a central core radius of about 550 nm. We numerically studied the effects of the misalignment of the different optical elements and the range of tilt and shift that are acceptable to obtain a regular Bessel beam.

Micro-Hole Generation by High-Energy Pulsed Bessel Beams in Different Transparent Materials.

Micro-drilling transparent dielectric materials by using non-diffracting beams impinging orthogonally to the sample can be performed without scanning the beam position along the sample thickness. In this work, the laser micromachining process, based on the combination of picosecond pulsed Bessel beams with the trepanning technique, is applied to different transparent materials. We show the possibility to create through-apertures with diameter on the order of tens of micrometers, on dielectric samples with different thermal and mechanical characteristics as well as different thicknesses ranging from two hundred to five hundred micrometers. Advantages and drawbacks of the application of this technique to different materials such as glass, polymer, or diamond are highlighted by analyzing the features, the morphology, and the aspect-ratio of the through-holes generated. Alternative Bessel beam drilling configurations, and the possibility of optimization of the quality of the aperture at the output sample/air interface is also discussed in the case of glass.