Growth and ultraviolet application of Li2B4O7 crystals: Generation of the fourth and fifth harmonics of Nd:Y3Al5O12 lasers

Abstract

A 2 in. diam single crystal of lithium tetraborate (Li2B4O7) was successfully grown by the Czochralski method. The crystal was free from macrodefects and had a dislocation density as low as 100/cm2. It had an excellent homogeneity of the refractive index and a wide transparency down to 170 nm. The optical damage threshold was 40 GW/cm2. Second-harmonic generation and sum frequency generation were investigated in association with the generation of the fourth and fifth harmonics of a Q-switched Nd:YAG laser. The conversion efficiency of the second-harmonic generation from the green (532 nm) light was 20%.

Low-temperature crystal structure, specific heat, and dielectric properties of lithium tetraborate Li2B4O7

“…For example in Ref. 61 samples, 4,66 where in a sample for a nonlinear optical device a small cusp at approximately 220 K was evident on thermal dependence of ⑀ c , whereas no effect was visible on a sample prepared for a SAW device. The origin of such discrepancies is not yet well understood but studies are in progress.…”

“…13 Li 2 B 4 O 7 shows photoluminescence, when excited with hard quanta 12 and rather high radiation resistance ͑ap-proximately 40 GW/ cm 2 ͒. 4 According to Ref. 14 the lithium tetraborate crystals have a Mohs hardness of 6 ͑quartz is 7͒, a low density ͑2.45 g / cm 3 ͒, acoustic velocities slightly faster than in LiNbO 3 and LiTaO 3 , a SAW reflectivity per stripe five times higher than in LiNbO 3 , LiTaO 3 , or quartz which suggests miniaturization of SAW devices.…”

“…Over long time lithium tetraborate, a member of the very rich borate family of crystals, attracted strong interest due to its exceptional optical properties. For example Li 2 B 4 O 7 has possible applications as a substrate material for bulk and surface acoustic wave ͑SAW͒ devices, 1,2 as a frequency-conversion material for second-fifth harmonic generation from a high-power Nd:YAG laser, [3][4][5] as a highpower ultraviolet light source based on second harmonic generation and sum frequency generation of the visible laser radiation, 6,7 Ag-doped or Cu-doped Li 2 B 4 O 7 crystals are used as thermoluminescence dosimeters, 8,9 as neutron detectors, 10 etc. Lithium tetraborate is a broadband dielectric with E g = 7.57 eV and a transmission range of 165-6000 nm, 11,12 where the boron-oxygen framework mainly contributes to the formation of levels in the upper region of the valence band.…”

Highly efficient acoustooptic diffraction in alpha-BaB2O4 crystals: improving of geometry of acoustooptic interaction

“…Crystals of borate family, such as 2 4 α-BaB O , 2 4 β-BaB O , 2 4 7 Li B O , 4 7 PbB O and 4 7 SrB O , are known as efficient materials for nonlinear optical applications (see [1][2][3][4][5][6]). A wide range of their optical transparency, particularly in the ultraviolet (UV) spectral region [7][8][9][10][11] (up to 125 nm for 4 7 SrB O [10, 11]), and a high level of optical damage threshold [11,12] make them one of the best materials for operation of short-wavelength high-power laser radiation.…”

Obliquity of the acoustic energy flow in acoustooptic alpha-BaB2O4 and Li2B4O7 crystals

“…These materials manifest a wide range of optical transparency (200-3000 nm for ABO and 200-6000 nm for LTB), high optical damage threshold, sufficient mechanical hardness and low hygroscopicity [1][2][3][4], which make them attractive for numerous applications in optoelectronics. Moreover, the LTB crystals are also known as an efficient material for the optical frequency multiplication, in particular for the deep UV region [5][6].…”