Search

International audience; The controlled laser energy deposition in dielectrics is a key technological issue for applications thatrequire drilling or structuring glass materials in the bulk. High angle Bessel beams delivered by a fem-tosecond laser have been used for extremely high aspect ratio nanochannels drilling and microstructuringin glass with a single laser shot [1,2]. Several types of filamentary damages were obtained with highangle Bessel beams and were reported to depend on laser pulse duration and energy [2]. I will addressthe question of optimal laser parameters for nonlinear absorption of laser energy in the bulk of dielectricmaterials, along the focal line of a Bessel beam.A semi-analytical model was developed for modeling the generation of a plasma column with fem-tosecond and picosecond laser pulses focused by a conical lens in dielectrics. The associated nonlinearabsorption of energy was calculated so as to highlight the influence of the pulse duration, laser pulseenergy and cone angle, on laser energy absorption. From a map of the density of nonlinear absorption oflaser energy in BK7 as a function of pulse duration and peak fluence, a specific pulse duration is shownto correspond to the highest nonlinear absorption at given pulse energy and cone angle. This durationcorresponds to a transition between two propagation regimes of the laser pulse featured by uniform ornon-uniform laser energy deposition in the Bessel zone. A uniform energy deposition is obtained in theabsence of pulse temporal dynamics.I will show that transmission measurements in BK7 are qualitatively well reproduced by the results ofthe semi-analytical model, which is also in agreement with numerical simulations of the nonlinear pulsepropagation

International audience; Ultrafast lasers have become a key tool for advanced structuring of glass and other transparent hard and brittle materials. In this context, it is crucial to control the propagation of the laser pulse inside the transparent medium while the complex laser-matter interaction renders it highly nonlinear.We have shown that a particular class of beam shapes, ie "diffraction-free" beams, enables a novel degree of control of light-matter interaction with a quasi-uniform deposition of energy in the material. This enabled for instance high-aspect ratio nanochannel drilling with a single laser pulse in various transparent materials [1]. We reported curved laser processing [2] or high-aspect ratio tubular shape inscription [3].We will review how the specific structure of nondiffracting and curved beams allows for controlling energy deposition in transparent materials and review their applications to laser materials processing of transparent materials [4].

International audience; Bessel beams provide a novel route for ultrafast laser processing of solid dielectrics. This is because even at high intensity, they do not undergo nonlinear distortions and allow uniform energy deposition along the beam path. We will review benefits of Bessel -like beams for laser micro and nano-structuring of transparent materials with high aspect ratio: glass and sapphire cutting, high aspect ratio void formation. Of particular interest is the impact of the transverse beam shape and polarization on the control of stress and cracks in glass and sapphire, leading to cleavage after single pass illumination.

International audience; Ultrafast laser materials processing has undergone an important change with the development of non-diffracting beams. These beams enable overcoming many of the difficulties usually encountered with standard Gaussian-beam focusing in materials. We review the techniques of non-diffracting and accelerating beam shaping that generates lines, tubes or curved segments of focused light on distances that exceed the Gaussian Rayleigh range by several orders of magnitude. We review the benefits and applications of nondiffracting beams for laser micro- and nano-processing in the general context of materials processing with ultrashort pulses in the filamentation regime. We highlight applications on ultra-high aspect ratio nano-drilling and direct laser processing along curves.

International audience; We review the state of the art of accelerating beams, discussing their properties from perspectives of geometrical optics, Maxwell’s equations and catastrophe theory, and surveying results from femtosecond material processing to random rogue wave generation.

International audience; Glass processing is an important technological problem since this class of material generates an increasing number of applications (solar calls, flat panel displays, microfluidics, optofluidics). In this context, the ability of femtosecond laser pulses to deposit energy in the bulk of transparent material is an important benefit for drilling, cleaving or index writing. At high intensities, femtosecond pulses in glass undergo Kerr self-focusing and interact with laser-generated free-electron plasma. Gaussian beams usually undergo strong spatio-temporal distortions during propagation in dielectrics.We investigate the propagation dynamics of Bessel filaments. They exhibit a regime that is distortion-free even at high intensity. To develop applications, it requires thorough comparisons between experiments and simulations. We have developed a novel 3D beam imaging technique allowing for direct and quantitative comparison between numerical and experimental beam fluence distributions in glass. We also report on the domain of existence of stationary femtosecond Bessel beams in dielectrics and the emergence of instabilities from studies both in near and far field. Applications to femtosecond laser processing will be reported.

International audience; Accelerating beams are a novel class of optical waves where the localized intensity maximum propagates along a curved trajectory with applications in nonlinear optics and optical manipulation. While initial studies of the paraxial regime have demonstrated Airy beams propagating along arbitrary trajectories, recent extensive work as focused on solutions of the wave equation in the nonparaxial regime. Two main approaches have been used to find the solutions. Derivation of exact solutions from Maxwell or Helmholtz wave equation provides closed-form solutions. However, another approach is based on the association of the target trajectory with an optical caustic, and this allows us to engineer a phase mask such that an incident beam further evolves on a predefined arbitrary nonparaxial trajectory. We report a method for accelerating beam generation in the Fourier domain and experimentally demonstrate arbitrary accelerating beam in two and three dimensions. Specifically, we report the experimental generation of optical beams propagating on the surface of a sphere of 50 µm radius and covering more than 95° of arc. In two dimensions, we also report the experimental generation of arbitrary accelerating beams with uniform illumination over more than a quadrant of a circle. Moreover, we show that our method is compatible with amplitude modulation and the generation of periodic accelerating beams is reported with excellent agreement with numerical simulations. Finally, we report the use of femtosecond laser machining of arbitrary curved profiles using nonparaxial accelerating beams.

International audience; Although versatile and widely used, femtosecond laser micro-nanomachining faces a challenge for the fabrication of high aspect ratio or deep structures. The control of the profile along the longitudinal dimension is extremely difficult. In this context, our approach is based on controlling the direction of light rather than shaping the intensity pattern in one plane. Here we review our recent work in this field using Bessel beams and accelerating beams. In Bessel beams, light propagates along the generatrix of a cone, with a fixed radial wavevector. Contrary to Gaussian beams, the femtosecond filamentation regime of Bessel beams can be stationary, and can generate extended plasma tracks in dielectrics. This allowed us to generate nanochannels in glass with aspect ratio up to 100:1 [1]. Numerical simulations of the nonlinear propagation in this regime show the importance of the conical structure in generating extremely dense plasmas [2]. Airy beams and more generally accelerating beams constitute another family of beams that possess quasi-nondiffracting behaviour and their nonlinear propagation can also be stationary. Their primary intensity lobe propagates along a curved trajectory that can be arbitrarily shaped even in the nonparaxial regime. Since this lobe is adjacent to a region where no light propagates, accelerating beams can be used for direct curved edge profiling and trench processing in transparent and opaque materials [3,4]. Our results show that controlling the linear and nonlinear propagation of ultrashort femtosecond laser pulses by nondiffracting beams is a key new technological approach for laser processing.

International audience; We review our recent results applying caustics wave theory to the generation of arbitrary curved accelerating beams and their use in the field of femtosecond laser materials processing. We report experimental realization of highly nonparaxial accelerating beams with circular, parabolic and quartic trajectories that extend over more than 95 degrees of arc as well as spherical optical fields. We also report femtosecond laser curved edge profiling.