Design of a full silica pulse compression grating

International audienceA diffraction grating engraved on a two-dimensional photonic crystal composed of square air holes in a silica matrix is numerically studied for the compression of ultra-short pulses. The silica is therefore the only solid material of the grating and the reflection of the incident beam is based on the contrast of the air and silica refractive indices. This optical component enables the single use of silica as a solid material presenting a high laser induced damage threshold. In comparison to gratings engraved on a dielectric stack (MLD), it offers the advantage of avoiding the presence of interfaces between 2 solid materials with different mechanical properties, sources of mechanical constraints which can distort the grating

Imaging subsurface damage of grinded fused silica optics by confocal fluorescence microscopy

International audienceWe report an experimental investigation of fluorescence confocal microscopy as a tool to measure subsurface damage on grinded fused silica optics. Confocal fluorescence microscopy was performed with an excitation at the wavelength of 405 nm on fixed abrasive diamond grinded fused silica samples. We detail the measured fluorescence spectrums and compare them to those of oil based coolants and grinding slurries. We evidence that oil based coolant used in diamond grinding induces a fluorescence that marks the subsurface damages and eases its observation. Such residual traces might also be involved in the laser damage process

Subsurface damage measurement of ground fused silica parts by HF etching techniques

International audienceDetection and measurement of subsurface damage of ground optical surfaces are of major concern in the assessment of high damage thresholds fused silica optics for high power laser applications. We herein detail a new principle of SSD measurement based on the utilization of HF acid etching. We also review and compare different subsurface damage (SSD) characterization techniques applied to ground and fine ground fused silica samples. We demonstrate good concordance between the different measurements

Effect of electric field on laser induced damage threshold of multilayer dielectric gratings

International audienceThis paper studies gratings engraved in multilayer dielectric stacks for ultra high intensity laser compressors application. We design various grating profiles with high reflected efficiencies for 1780 l/mm multilayer dielectric gratings (MLD). Each grating is defined to exhibit a different electric field maximum value in the pillars of the grating. A damage testing facility operating at 1.053 μm, 500 fs pulse duration is used to damage test the parts manufactured from these designs. It is evidenced that for fixed incident angle and materials the damage of the grating is directly related to the electric field intensity maximum in the material, which depends on the groove profile. Laser induced damage thresholds of 5 J/ cm2 are experimentally reached with very high and uniform efficiencies

Pulse compression gratings for the PETAL project: a review of various technologies

International audienceA Petawatt facility called PETAL (PETawatt Aquitaine Laser) is under development near the LIL (Ligne d'Integration Laser) at CEA Cesta, France. PETAL facility uses chirped pulse amplification (CPA) technique. We herein review various studies made to develop pulse compression gratings for CPA application with high laser induced damaged threshold. Different multilayer dielectric (MLD) gratings have been manufactured to exhibit different electric field maximum values in the pillars of the grating. A damage testing facility operating at 1.053μm, 500fs pulse duration is used to damage test the parts manufactured from these designs. It is evidenced that for fixed incidence and materials the damage of the grating is directly related to the electric field intensity maximum in the material, which depends on the groove profile. Laser induced damage thresholds of 5 J/ cm2 is experimentally reached with very high and uniform efficiencies. New structures are currently under study, gratings with mixed metal/dielectric layers MLD or more exotic 2D and 3D photonic crystals devices. For each case, we detail the design and expected performances. We also give some diffraction efficiency and laser damage measurements when samples were manufactured

Design, optimization and development of pulse compression gratings for the MPHE-LIL

International audienc

Polishing-induced contamination of fused silica optics and laser induced damage density at 351 nm

International audienceIn this paper we study the effect of contamination induced by fabrication process on laser damage density of fused silica polished parts at 351 nm in nanosecond regime. We show, owing to recent developments of our raster scan metrology, that a good correlation exists between damag