Ryuichi Komatsu

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.

Application of the nonlinear crystal SrB4O7 for ultrafast diagnostics converting to wavelengths as short as 125 nm

We used non-phase-matched second-harmonic generation (SHG) in the highly nonlinear but low-birefringence crystal SrB4O7 for temporal characterization (autocorrelation) of femtosecond UV pulses to convert these pulses to wavelengths as low as 125 nm, close to the transparency limit of SrB4O7. The sensitivity of this method was approximately 1 microJ at the fundamental for a repetition rate of 1 kHz. We also used SHG at longer wavelengths to estimate the three nonlinear coefficients of SrB4O7.

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.

EPR and optical studies on transition metal doped LiRbB4O7 glasses

Abstract Electron paramagnetic resonance and optical investigations of copper and chromium doped LiRbB 4 O 7 glasses are carried out. From the results and discussions, it is predicted that both the transition metal ions exhibit octahedral environment. In the case of Cr 3+ , the site symmetry is near octahedral, whereas in the case of Cu 2+ , it is tetragonally distorted octahedral environment. Crystal field, spin-Hamiltonian and bonding parameters are evaluated. The bonding parameters are suggesting ionic.

Frequency conversion of Ti:sapphire-based femtosecond laser systems to the 200-nm spectral region using nonlinear optical crystals

We review the linear and nonlinear optical properties of crystals transparent near and below 200 nm and suitable for up conversion of femtosecond Ti:sapphire laser sources, /spl beta/-BaB/sub 2/O/sub 4/, the crystal with the largest birefringence of all presently available materials, is investigated experimentally as a quadrupler by mixing the fundamental and the third harmonic both using a 1-kHz repetition rate Ti:sapphire regenerative amplifier and a 82-MHz mode-locked Ti:sapphire laser. Milliwatt average powers near 200 nm are achieved in both cases. The sub-200-fs pulses at the fourth harmonic are almost bandwidth limited. Sum-frequency generation as a method for upconversion of femtosecond pulses is experimentally studied by mixing the fourth harmonic generated down to 189 nm by the regenerative amplifier with a parametrically generated femtosecond pulse in the infrared. Pulse energies at the microjoule level are produced with LiB/sub 3/O/sub 5/ above 180 nm. Li/sub 2/B/sub 4/O/sub 7/ shows superior performance in the 170-180-nm range, and the shortest wavelength achieved with KB/sub 5/O/sub 8//spl middot/4H/sub 2/O is 166 nm.

Crystallization behavior and characteristics of mullites formed from alumina–silica gels prepared by the geopolymer technique in acidic conditions

Abstract Mullites were prepared by the geopolymer technique to obtain nanometer sized mullite polycrystals. Sodium silicate solutions prepared from Na 2 O·SiO 2 ·9H 2 O (A-series) and Na 2 O·2SiO 2 ·aq (B-series) were applied as host solutions. Then, Al-nitrate guest solution was added drop by drop into the host solutions to obtain precipitates, which were filtrated and washed by deionized water. The air-dried precursor gels thus obtained were fired at elevated temperature up to 1400°C and were examined by XRD, DTA and ICP techniques. The XRD results showed that the A-series gels began to crystallize mullite at about 1000°C, while the B-series at about 1100°C. According to the DTA, a sharp exothermic peak appeared at about 1000°C in the A-series gels indicating polymer character of the gels, while no such a peak in the B-series gels indicating nonpolymer character of the gels. Chemical analysis by ICP revealed low concentration of Al 2 O 3 -component in the gels, and this caused the gels consisted of mullite and silica potentials. Na-contaminations were extremely low. The process of mullite generation was also discussed on the basis of cell-parameters measured.

Electron paramagnetic resonance and optical absorption spectra of Cr3+ ions in cadmium phosphate glass

EPR and optical absorption investigations of chromium doped cadmium phosphate glass are carried out. Crystal field, spin-Hamiltonian and bonding parameters are evaluated. From the results and analyses of the EPR and optical studies, the site symmetry of Cr 3+ ion in the glass is ascribed to a distorted octahedron. The bonding parameters suggest the ionic nature of Cr 3+ ion with the ligands.

Spectroscopic studies of copper-doped ARbB4O7 (A=Na, K) glasses

Abstract EPR and optical absorption investigations are carried out at room temperature on copper-doped ARbB4O7 (A=Na, K) glasses. The results indicate that the copper ions (Cu2+) enter the glass matrix into a tetragonally elongated octahedral site. Crystal field and spin-Hamiltonian parameters are evaluated. The bonding parameters indicate that bonding between the metal ions and ligands is partially covalent.