he generation of UV light by means of nonlinear optical (NLO) processes from an infrared fundamental beam is indeed a promising path to design all solid-state UV lasers. Such solid state devices should replace the current excimer lasers and would find a large number of applications (medical surgery, micro photolithography microelectronics etc..). For this purpose, several nonlinear optical crystals have to be used, but there are only very few NLO crystals that can achieve the last stage of frequency conversion towards UV, especially when wavelengths below 270 nm are targeted. Two families of crystals with real potentialities have been studied. They are based on YAl3(BO3)4 (YAB) and Ca5(BO3)3F (CBF). These crystals have been developing to compete with the commercial crystals, which are practically used today for UV conversion (LBO, BBO or CsLiB6O10 (CLBO)) but have some severe drawbacks regarding hygroscopic short lifetime in UV laser systems. We have investigated the crystal and nonlinear optical properties of (CBF) and (YAB) using Top Seeded Solution Growth methods. Single crystals of (CBF), have been grown by the flux method with LiF. This monoclinic compound was investigated for nonlinear optical applications and was expected to exhibit an extended transparency window in the ultraviolet. Its refractive indices were measured and fitted to the Sellmeier equations to calculate the phase matching angle curves. We demonstrate 300 mW of UV average power generation at 343 nm by frequency-tripling using CBF crystal cut along the two possible phase matching configurations for third harmonic generation in plans XY and YZ. YAB single crystals were grown using the top seeded solution growth (TSSG) method with La2O3-B2O3-LiF as a flux . A YAB slab of dimensions 15 x 15 x 2.94 mm3 was cut in ZX plane with θ= 66.9 ° and φ = 0° for type I SHG leading to 266 nm generation. Using a Q-switch microchip laser Nd:YAG/Cr4+:YAG frequency doubled with a LiB3O5 (LBO) crystal, 240 kW peak power at 266 nm corresponding to an average conversion efficiency of 12.2% from 532 to 266 nm has been obtained with a 2.94 mm thick YAB crystal. More recently improvement of the optical quality of YAB crystal enables the highest UV power of 1.8 MW and shortest pulse of 118 ps with power conversion efficiency of 37 % at 266 nm by using LBO crystal and Nd:YAG/Cr4+:YAG microchip laser. The influences of optical homogeneity and absorption on the conversion efficiency will be discussed.

Nonlinear optical borates based oxides for solid state laser frequency conversion in the UV range

253rd National Meeting (2017)

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