Crystalline Flat Surface Recovered by High-Temperature Annealing after Laser Ablation

Abstract

Ultra-short laser pulses (1030 nm/230 fs) were used to laser ablate the surface of crystalline sapphire (Al2O3) at high intensity per pulse 20–200 TW/cm2/pulse. Laser-ablated patterns were annealed at a high temperature of 1500 °C. Surface reconstruction took place, removing the ablation debris field at the edges of ablated pits in oxygen flow (O2 flow). Partial reconstruction of ripples was also observed when multi-pulse ablated surfaces were annealed at high temperature in O2 flow. Back-side ablation of a 0.5-mm-thick Al2O3 produced high surface roughness ∼1μm which was reduced to ∼0.2μm by high-temperature annealing at 1500 °C for 2 h in O2. Improvement of surface quality was due to restructuring of the crystalline surface and sublimation, while the defined 3D shape of a micro-lens was not altered after HTA (no thermal morphing).

Enhanced Yb:YAG Active Mirrors for High Power Laser Amplifiers

“…(T(z, r, t) − T bound )dz, (6) where dn 0 dT is the thermo-optical coefficient of a garnet crystal, K −1 ; n 0 is the refractive index of the crystal before pumping is turned on; α T is the coefficient of thermal expansion; C r is the photoelastic constant; υ is the Poisson's ratio; T bound is the temperature of the cooled face, K; L is the length of the active element, cm.…”

“…The development of high-intensity laser systems has made it possible to carry out fundamental interdisciplinary research based on the nonlinear interaction of radiation with matter, including such directions as the generation of high-order harmonics [1] and attosecond pulses [2], laser acceleration of charged particles [3], and others [4][5][6][7]. Contemporary research in the area of laser technologies is aimed at achieving the high pulse repetition rate required for many applications [8] and at increasing the amplification efficiency in laser amplifiers.…”