RESUMEN
The Laser Megajoule (LMJ) is among the most energetic inertial confinement fusion laser facilities in the world, together with the National Ignition Facility (NIF) in the USA. The construction of the facility began back in 2003, and the first photons were emitted by the laser bundle #28 in 2014. Today, 11 laser bundles consisting of 88 large aperture 0.35×0.35m 2 laser beams are in operation, delivering daily up to 330 kJ of energy at the wavelength of 351 nm on a target placed in the center of a 10 m diameter vacuum chamber. In this paper, we describe the laser system and its operational performances. We also detail the first laser campaigns carried out to prepare an increase of energy and power on the target. These campaigns, along with the completion of additional bundles mounting, will bring LMJ performance to 1.3 MJ thanks to 22 bundles in operation.
RESUMEN
We report on a functional experimental design for Bessel beam generation capable of handling high-energy ultrashort pulses (up to 1.2 mJ per pulse of 50 fs duration). This allows us to deliver intensities exceeding the breakdown threshold for air or any dielectric along controlled micro-filaments with lengths exceeding 4 mm. It represents an unprecedented upscaling in comparison to recent femtosecond Bessel beam micromachining experiments. We produce void microchannels through glass substrates to demonstrate that aspect ratios exceeding 1200â¶1 can be achieved by using single high-intensity pulses. This demonstration must lead to new methodologies for deep-drilling and high-speed cutting applications.
RESUMEN
The laser-induced damage growth phenomenon is experimentally studied for damage sites on the exit surface of fused silica. The sites are irradiated by nanosecond laser pulses at 1064 and 355 nm separately and also simultaneously. The results in the single wavelength configurations are expressed in terms of the probability of growth and growth coefficient. For growing sites, a fluence correction expression is proposed in order to take into account the millimetric Gaussian profile of the beams. The use of this expression is necessary to obtain results that are consistent with the ones obtained in the existing literature with large homogeneous beams. In the multiple wavelengths configuration, the results are expressed as a function of the laser fluences at each wavelength and are found to be closely related to the parameters determined in the single wavelength experiments. A coupling between the two wavelengths is quantified, and could originate from the formation and the expansion of a plasma produced both in the center and at the periphery of the damage sites.
RESUMEN
An important challenge in the field of three-dimensional ultrafast laser processing is to achieve permanent modifications in the bulk of silicon and narrow-gap materials. Recent attempts by increasing the energy of infrared ultrashort pulses have simply failed. Here, we establish that it is because focusing with a maximum numerical aperture of about 1.5 with conventional schemes does not allow overcoming strong nonlinear and plasma effects in the pre-focal region. We circumvent this limitation by exploiting solid-immersion focusing, in analogy to techniques applied in advanced microscopy and lithography. By creating the conditions for an interaction with an extreme numerical aperture near 3 in a perfect spherical sample, repeatable femtosecond optical breakdown and controllable refractive index modifications are achieved inside silicon. This opens the door to the direct writing of three-dimensional monolithic devices for silicon photonics. It also provides perspectives for new strong-field physics and warm-dense-matter plasma experiments.Ultrafast laser processing is a versatile three-dimensional photonic structuring method but it has been limited to wide band gap materials like glasses. Here, Chanal et al. demonstrate direct refractive-index modification in the bulk of silicon by extreme localization of the energy deposition.