Tamotsu Sugawara

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

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%.

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.

Structural study of LiKB4O7 and LiRbB4O7: New nonlinear optical crystals

The title compounds, LiKB 4 O 7 (LKB4) and LiRbB 4 O 7 (LRB4), are newly developed nonlinear optical crystals containing two kinds of anionic groups, (B 3 O 8 ) 7- and (B 5 O 10 ) 5- . The (B 3 O 8 ) 7- groups form infinite spiral chains parallel to the [100] direction, which are interconnected by sharing oxygen atoms with (B 5 O 10 ) 5- groups.

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.

Lithium potassium borate and lithium rubidium borate: new non-linear optical crystals

The title compounds, LiKB(4)O(7) and LiRbB(4)O(7), are newly developed non-linear optical crystals containing two kinds of anionic groups, namely (B(3)O(8))(7-) and (B(5)O(10))(5-). The (B(3)O(8))(7-) groups form infinite spiral chains parallel to the [100] direction, which are interconnected by sharing O atoms with (B(5)O(10))(5-) groups.

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 3-Inch-Diameter Li2B4O7 Single Crystal Using the Resistance Heating Furnace

The mode and origin of cracking of lithium tetraborate (Li 2 B 4 O 7 ) single crystals during growth using a resistance heating furnace have been studied. The relationship between the formation mechanism of anomalous growth ridges and the occurrence of cracking was examined. It is concluded that a high temperature gradient near the interface and small temperature fluctuations in the melt are needed for growing a crack-free 3-inch-diameter Li 2 B 4 O 7 single crystal

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.

Consideration of Small Variation of Surface Acoustic Wave (SAW) Velocity in Lithium Tetraborate

It has been experimentally revealed that the variation of surface acoustic wave (SAW) velocity in lithium tetraborate crystals is smaller than that in other SAW crystals. This may relate to the small deviation of lattice constant due to the little change in chemical composition of the wafer. Such homogeneity can be explained by the specific compositional properties of Li2B4O7 crystal and its melt.

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.