This article focuses on the top-seeded solution growth (TSSG) of single crystals of the low-temperature non-centrosymmetric modification of barium borate, β-BaB2O4 (β-BBO), using a mixed solvent comprising NaBaBO3 and V2O5. We examine the linear absorption properties across a wide spectral range and nonlinear second harmonic generation (SHG) from 532 nm to 266 nm in β-BBO samples under Nd:YAG laser radiation pumping. The mean linear absorption for ordinary waves in vanadium-based crystals at wavelengths from 300 to 600 nm is found to be an order of magnitude higher than that in standard samples, measuring 0.0059 and 0.0007 cm-1, respectively. However, crystals grown from the proposed vanadium-based solution still exhibit similar SHG efficiency to standard samples. Deviations from the quadratic dependence are observed at pump power densities exceeding 20 MW/cm2, possibly attributed to temperature effects resulting from insufficient temperature stabilization.
Lithium triborate crystals LiB3O5 (LBO) considered as a high efficiency nonlinear material that is applied to transform laser beam frequency. The most effective application of the crystal is the transformation of neodymium based laser with 1064nm wavelength to the second and to the third harmonic generation. The high damage threshold and operation characteristics of LBO are the reasons to use it in wide-aperture high-power laser systems with aperture diameters up to several cm. Experimentally it was verified that improved crystal growth technique allows to grow the crystals that are given the opportunity to enlarge the dimensions of nonlinear elements by modifying the ratio of the grown crystal dimensions, i.e. habitus.
Comparative analysis of optimal scheme of non-collinear optical chirped-pulse parametric amplification of fewcycle
femtosecond pulses from Ti:Sa laser in LBO and DKDP crystals pumped by picosecond pulses up to petawatt level
is presented. A flexible code, based on the extended model of parametric amplification, which takes into account the
large set of effects such as saturation, phase self-modulation, influence of beam divergence, thermal effects, and
amplification of spontaneous emission was realized. A way of creating nearly 1 PW system based on LBO crystals with
transform-limited pulse duration about 9 fs has been demonstrated. Comparison between DKDP and LBO crystal
showed that the latter is much better for OPCPA petawatt system design than DKDP.
In the last one and a half decade crystals of barium metaborate (β-BaB2O4 or BBO) have been widely applied in non-linear optics and electro-optics. The growth of BBO is a technologically sophisticated procedure enabling the production of big high-quality single crystals. The best results have been obtained by growing BBO with top-seeded solution growth (TSSG) method in the BaO-B2O3-Na2O ternary system. The typical effect of constitutional supercooling results from a high viscosity of the melt-solution and the fact that a growing BBO crystal shields the crystallizing melt, thus weakening convective flows and removing heat away from crystallization interface. The contribution considers the possibility of the improvement of crystal growth process via the change of heat field symmetry and its rotation. Such the nonconventional approach has allowed to carry out the contact free structurization and intensification of convective flows in the melt-solution body and by that to reach more complete crystallization of a material increasing the yield before effect of constitutional supercooling. In that way we grow BBO crystals, from which it is possible to make non-linear optical elements of 15x15x15 mm3 sizes and electro-optical elements for Pockels cell with 6x6x22 mm3 sizes along an optical axis.
BBO crystals ((beta) -BaB2O4) exhibit unique nonlinear- and electro-optical properties, which provide their wide application in laser techniques. The growth of BBO is a technologically sophisticated procedure enabling the production of big high-quality single crystals. The growth of BBO crystals is performed with high-temperature melt-solution crystallization method, most commonly in the BaO-B2O3- Na2O ternary system. The typical effect of constitutional supercooling results from a high viscosity of the melt- solution and the fact that a growing BBO crystal shields the crystallizing melt, thus removing heat away from crystallization interface. The contribution considers the possibility of the improvement of crystal growth process via the change of heat field symmetry and its rotation. The symmetry of a static heat field reducing from Lvaries direct as to L3 results in stronger convection and, therefore, larger crystal. On the other side the permanent symmetry of a heat field -- static or rotating -- commonly provokes the formation of a quite big defect area in the central part of a grown boule with the signs of cell growth. To improve the convection in the central sub-crystal area we performed the BBO crystal growth process in a rotating heat field, which is free of the symmetry axis coinciding with the symmetry axis of the growth furnace/crucible. The experiments showed that the crystal with a defect-free central area can be successfully produced.
An area of CsLiB6O10 (CLBO) phase equilibrium in the (Cs2O-Li2O) -- B2O3 -- MoO3 system was determined with spontaneous crystallization method. Crystals of 75 X 60 X 40 mm3 size have been growth in [100] direction with Kiropulos method. The forth-harmonic generation (270 nm) was achieved through the doubling of second-harmonic frequency in a multi-mode Nd:YAP laser in the type 1 collinear phase-matched geometry. The second-harmonic radiation in the technological laser of 3 mrad divergence was focused onto the input face of the crystal by a long-focus quartz lens. The input power density of the second harmonic was 300 MW/cm2. Using a 11.5 mm crystal, we showed that the highest efficiency of the forth-harmonic generation is 30%. The fifth harmonic (216 nm) in CLBO crystal was generated by composing the main laser beam and the forth-harmonic beam under the type 1 collinear phase-matching. Both beams were converged with dichroic and turning mirrors and then focused by a long-focus quartz lens. Our experiments showed that the fifth-harmonic generation in a multi-mode technological laser of 3 mrad divergence is possible in a 10 mm CLBO crystal of 23% optical conversion efficiency. The input power density of the forth harmonic was 100 MW/cm2. The use of longer CLBO crystal is less effective due to the nonlinear UV absorption and the walk off between the pump beam (1079 nm) and the harmonic beam.
CsLiB6O10 (CLBO) is a highly promising nonlinear optical material. However, its application is limited due to the difficulties in producing optically uniform CLBO crystals. High viscosity of Cs2O-Li2O-B2O3 melt retards both natural and forced convection in the melt. With the goal to improve the heat and mass transfer in the melt, the study of crystallization in the Cs2O-Li2O- B2O3-MoO3 system was carried out. The CLBO crystals 60 X 40 X 20 mm in size grown using LiCsMoO4 as a solvent were found to be free of cracks, bubbles, and inclusions. Nonlinear optical parameters and physical properties of those crystals turned out to be similar to those reported before. Mohs' hardness is 5.5, transparency window ranges from 0.18 to 2.7 micrometers , nonlinear coefficient is 1 pm/V, angular and spectral bandwidth of synchronism are 0.5 mrad-m and 0.1 nm-cm. The walk-off angle is 2 degree(s) at 0.53 micrometers . The nonlinear optical elements for the 4th harmonic of Nd:YAG laser were fabricated and tested.
BBO crystals were grown by the top-seeded solution growth technique from a Na2-O melt-solution. Optimization of heating conditions and technological growth parameters allowed us to produce high-quality optic crystals. Their main morphological feature is the facing of a boule side surface. The area of hexagonal prism face {1120} can reach several square centimeters. Non-linear-optical elements which are produced from a crystal with well arranged faces have higher coefficients of laser radiation frequency conversion. The BBO crystals were studied for linear and non-linear absorption. Linear absorption was measured with conventional spectroscopic method. The analysis of supplementary absorption spectra and thermally- stimulated luminescence behavior allowed us to suggest that Na atoms are a main spontaneous impurity in BBO crystals providing supplementary absorption in UV-region. We used the 4th and 5th harmonics of Nd-YAG laser to measure the non-linear absorption. The selected optimized crystals were used in various optical schemes up to the 5th harmonic generation. Harmonic generation was studied by high performance original Nd-YAG laser (SLM-operation, D. L. output beam up to 100 Hz repetition rate, 1.8 ns pulse duration, 16 W output). Harmonic efficiency values are listed below. Several optical schemes for harmonic generation are discussed.
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