Application of Bessel beams for ultrafast laser volume structuring of non transparent media

Abstract

The use of ultrashort laser pulses has been shown to be an attractive option for high quality micromachining. In these applications low energy laser pulses are tightly focused to achieve high light intensities. While this approach has been demonstrated to be successful, its application is challenged by the short Rayleigh range of a tightly focused laser beam. Precise positioning of material samples becomes crucial imposing extra requirements on sample flatness, tilt, and irregularities. To overcome some of these limitations an application of non-diffractive Bessel beams for laser material processing has been attempted recently. The non-diffractive focus of Bessel beams can have the depth of field significantly longer than the Rayleigh range of a Gaussian beam of a comparable diameter. With sub mJ laser pulse energy the light intensity along the line focus can reach and exceed the required threshold levels making laser Bessel beams suitable for material processing. Preliminary numerical simulations show that truncated by a micron size aperture Bessel beam still has the propagation depth sufficiently long to be suitable for volumetric micro structuring of non transparent media. The paper aims to demonstrate feasibility of ultrafast laser structuring of non transparent media using Bessel beam focusing geometry.