Ultrafast laser processing of dielectrics: Beyond single shot Bessel beams

International audienceUltrafast lasers have been a revolution in a number of areas of science and technology. In materials processing,the ultrafast pulse duration brought the ability to deposit energy into the free-electron gas before it couples to thelattice and therefore generate extremely steep thermodynamic gradients. A second benefit is the ultra-high peakpower which allows for ionizing dielectrics, even from the bulk material. The processing of glass and sapphire isof particular importance for several technological applications to mass fabrication (consumer electronics,microelectronics, etc). In this field, nondiffracting Bessel beams have brought the ability of controlling energydeposition by a single laser pulse on a long propagation distance inside dielectrics. In particular, this has allowedavoiding nonlinear instabilities generated by the filamentation regime of Gaussian beams yielding inhomogeneousdamage in materials [1]. Here, we report further advances in this field where additional benefit can be found in other beam shapes andpulse sequence. For applications to the so-called "stealth-dicing" technology, where material is cleaved after laserillumination, we have developed elliptical Bessel beams. We have demonstrated these beams remain alsopropagation-invariant and allow for generating nanochannels with elliptical cross section (Fig. 1(a)) [2]. We havedemonstrated those allow for cleaving glass (Fig 1(b)) with enhanced reliability and with sub-μm accuracy [3].In addition, we will discuss recent novel results where the illumination has been performed by double pulses withequal power. We show that, depending on the initial pulse energy, double femtosecond pulses enhance the abilityof channel drilling in glasses. In particular, channels with larger diameters are produced [4]. Energy absorptionmeasurements will be discussed