Satoshi Uda

Linear and nonlinear optical properties of lithium tetraborate

Abstract The refractive indices of Li 2 B 4 O 7 crystal were measured for both ordinary and extraordinary beams in the range of 184.887 nm–2325.42 nm, and the Sellmeier equations were derived from these results. Li 2 B 4 O 7 crystal has a suitable phase-matching condition in the ultraviolet range and the shortest SHG output wavelength of 243.8 nm. Considering also its short-wavelength cutoff and low scattering, Li 2 B 4 O 7 crystal is an excellent nonlinear optical crystal for an ultraviolet solid-state laser.

Vacuum ultraviolet application of Li2B4O7 crystals: Generation of 100 fs pulses down to 170 nm

We investigate and characterize the newly grown crystal Li2B4O7 which is transparent down to 160 nm for nonlinear optical conversion into the vacuum ultraviolet using sum frequency mixing with femtosecond pulses. This material exhibits excellent properties below 180 nm and makes possible the generation of wavelengths down to 170 nm with an all solid state laser system. The most important advantage of Li2B4O7 in this spectral range turns out to be the possibility of utilizing noncritical phase matching with maximized effective nonlinearity. We demonstrate generation of nearly transform limited 100 fs pulses between 170 and 185 nm with conversion efficiency of 4%. Their peak powers range from 200 kW at 170 nm to >2 MW at 185 nm.

Phase relations around langasite (La3Ga5SiO14) in the system La2O3–Ga2O3–SiO2 in air

Abstract Phase relations around langasite (LGS, La 3 Ga 5 SiO 14 ) were studied on the basis of phase assemblage observed during calcination and crystallization process of samples of various compositions in the ternary system La 2 O 3 –Ga 2 O 3 –SiO 2 . A ternary compound of apatite structure, La 14 Ga x Si 9– x O 39– x /2 was found for the first time. Crystallization of this compound was observed in the cooling process of molten samples of stoichiometric LGS as well as LGS single crystal, demonstrating that LGS is an incongruent-melting compound. A phase diagram was established primarily based on the crystallization sequence in the cooling process.

Nonlinear optical properties of langasite crystal

The parameters in the Sellmeier equation for langasite are accurately obtained on the basis of the measurement of the ordinary and extraordinary refractive indices in the region of 500 nm to 2500 nm, and the phase-matching of langasite is investigated. The second harmonic generation (SHG) of langasite is also examined by the Maker fringe method.

Growth of Crack-Free 3-Inch-Diameter Lithium Tetraborate Single Crystals by Czochralski Method

The growth of crack-free 3-inch-diameter lithium tetraborate (Li 2 B 4 O 7 ) single crystals by the Czochralski method has been studied. The relationships between crystal cracking rate during growth and the crystal rotation rate and the position of the work-coil have been examined. It is concluded that crystal cracking at a later stage of growth is related to the temperature fluctuation in melt

Development of Platinum Dendrite in Lithium Tetraborate Crystal Grown by the Czochralski Method

Platinum dendrites were found in lithium tetraborate crystals grown by the Czochralski method using a platinum crucible. The mode of occurrence and formation mechanism of platinum dendrite in lithium tetraborate were examined. It is revealed that platinum dendrites developed in the cellular structure that occurred during growth. The formation of platinum dendrite that is discussed is associated with the growth condition leading to cellular growth. The morphology of platinum dendrite is also explained by its specific crystallographic symmetry.

Mode of Occurrence and Cause of Twinning in Lithium Tetraborate Grown by Czochralski Method

Mode of occurrence and cause of twinning, which are occasionally observed in lithium tetraborate crystals grown pararell to [110], have been investigated. Twinning is related to the crystal symmetry, i.e., 4-fold screw axis along the c-axis. Relashionship between the cause of striations in crystals and the occurence of twinning during growth has also been examined in connection with temperature fluctuations near the interface.

Growth of crack-free lithium tetraborate (Li2B4O7) single crystals

Abstract The mode of occurrence and the origin of cracking of lithium tetraborate (Li2B4O7) during growth by CZ method have been investigated. It is considered that crystal cracking can be divided into two main modes of occurrence. Each origin of cracking have been examined; 3-inch-diameter crack-free Li2B4O7 have been successfully grown.

Heteroepitaxial growth of metastable ErF3 on CaF2(1 1 1) by molecular beam epitaxy: a novel material for optical upconversion

Abstract The heteroepitaxial growth of hexagonal ErF 3 onto CaF 2 (1 1 1) substrates using the molecular beam epitaxy (MBE) method is reported for the first time. Results of the X-ray rocking-curve (XRC) analyses showed the presence of the epitaxial relationship as (0 0 0 1) ErF 3 |(1 1 1) CaF 2 . Reflection high-energy electron diffraction (RHEED) investigation suggests the growth of hexagonal metastable ErF 3 with the epitaxial relationship of (0 0 0 1) ErF 3 |(1 1 1) CaF 2 , (0 1 1 0) ErF 3 |(1 1 2) CaF 2 , (2 1 1 0) ErF 3 |(0 1 1) CaF 2 . Detailed analysis of RHEED pattern elucidates that the metastable ErF 3 has the space group setting of P6 3 /mmc, and among the several models proposed for LaF 3 -type structure, this setting is the unique one which is consistent with the observation of RHEED patterns. The up-conversion property of ErF 3 for green-light emission ( λ = 538 nm) pumped by an AlGaAs diode laser ( λ = 798 nm) is investigated.

Factors Influencing the Variation of Surface Acoustic Wave Velocity in Lithium Tetraborate.

Comparison of the resonance frequency of surface acoustic wave (SAW) resonators fabricated on defect-free and highly defective lithium tetraborate wafers was attempted. The intrinsic variation of SAW velocity due to crystal defects, impurities and chemical compositional inhomogeneities for lithium tetraborate wafers is smaller than ± 0.011%. In addition, the variation of SAW velocity in a wafer is influenced by tlle device fabrication process rather than tlle lithium tetraborate substrate quality.