Masayoshi Sato

Increased optical damage resistance in Sc2O3‐doped LiNbO3

The optical damage of 1 mol % Sc2O3‐doped LiNbO3 was approximately two times smaller than an optical grade LiNbO3 measured as a function of Ar+ (λ=488 nm) irradiation time. Severe Ar+ beam distortion observed in the undoped LiNbO3 was not present in the Sc2O3‐doped LiNbO3. There was negligible shift in the OH− absorption band but a 10 nm blue shift was observed in the absorption edge, indicating that Sc3+ and Mg2+ incorporation may proceed by a different mechanism. This is the first of reported results, to the authors’ knowledge, of a trivalent dopant increasing the damage resistance level in LiNbO3.

Optical damage resistance and crystal quality of LiNbO3 single crystals with various [Li]/[Nb] ratios

Lithium niobate single crystals with various [Li]/[Nb] ratios were grown by the Czochralski method from melts having compositions varying between 45.5–58 mol % Li2O. Their optical damage resistance was characterized by measurement of the photoinduced birefringence change. Their crystal quality was characterized by x‐ray topography and x‐ray rocking curves. The photoinduced birefringence change increased with an increase in the Li content of the crystal. The Li‐poor crystals, which were richer in Nb content than the crystal with the congruent composition, showed the smallest birefringence change, in spite of the fact that the x‐ray rocking curve width of these Li‐poor crystals was much wider than the congruent crystal. It is concluded that the optical damage resistance of undoped LiNbO3 is increased with an increase in the Nb content of the crystal, and that the crystal quality, as represented by x‐ray rocking curve peak width, has no correlation with the optical damage resistance.

Growth and characterization of MgO-doped LiNbO3 for electro-optic devices

Magnetic and Electronic Materials Research Laboratory, Hitachi Metals, Ltd., Kumagaya, Saitama 360, Japan Two inch diameter LiNbO 3 crystals doped with MgO with no subgrain boundaries were successfully grown along the Z - and Y-axes under optimized growth conditions using the Czochralski technique. The resistance to optical damage induced by Ar-laser irradiation was measured by the change in birefringence using Senarmonts method. The birefringence change was found to increase proportionally with the concentration of Fe impurity in conventional SAW and optical grade crystals. No optical damage was observed in MgO doped LiNbO 3 single crystals under an incident power of 44 W/cm 2 and an exposure time of up to 10 min. Thus, it is concluded that MgO doped crystals have remarkably stronger resistance to optical damage than undoped crystals. The optical properties and distribution of Mg in the crystals were also investigated.

Investigation of the bulk laser damage of lithium triborate, LiB3O5, single crystals

The bulk laser damage threshold of lithium triborate (LiB3O5) single crystals were determined to be 45.0 GW/cm2 at 1.064 μm, 1.1 ns pulse width. The damage threshold was dependent on pulse duration and wavelength: at 1.064 μm, 25 ns the damage threshold was 11.2 GW/cm2, at 0.532 μm, 1.0 ns the damage threshold was 26 GW/cm2; and at 0.355 μm, 0.9 ns the damage threshold was 21.9 GW/cm2. To the best of our knowledge this is the highest value reported among inorganic frequency conversion crystals, and approximately 1.8 times higher than that of fused silica.

Top-seeded solution growth of LiB3O5

We report on the top-seeded solution growth of LiB3O5 from an excess B2O3 solution. Parameters investigated include the Li2O/B2O3 ratio, rotation rate, pulling rate, cooling rate, and seed direction. With careful control of the above parameters, we have grown clear crystals of 25 × 30 × 20 mm in size. Selected nonlinear optical properties of these crystals are reported. Observations concerning the occurrence of unstable growth (inclusions, hopper growth) are discussed, and methods to eliminate the unstable growth are suggested.

Growth and characterization of off-congruent LiNbO3 single crystals grown by the double crucible method

Off-congruent LiNbO 3 single crystals were grown from melts with Li-rich compositions (58.0 mol% Li 2 O) by using the double crucible method. The composition of crystals grown from melts with 58 mol% Li 2 O was found to be 49.8 mol%, close to the stoichiometric composition. The compositional variation throughout the crystal grown by the double crucible method was measured to be within 0.094 mol% by the results of SHG phase-matching temperature measurements. X-ray topography, X-ray rocking curves and extinction ratios indicate that the crystal quality of the off-congruent crystal is lower than that of the congruent crystal

Fabrication of periodically inverted domain structures in LiTaO3 and LiNbO3 using proton exchange

We report on the fabrication of a first‐order periodically inverted domain structure in LiTaO3 and LiNbO3 for quasi‐phase‐matched devices using proton exchange with one‐directional heating. First‐order periodically inverted domains with a 3.2 μm period and more than 40 μm depth were formed beyond the proton exchanged region. This domain inversion took place during the proton exchange process, far below the Curie temperatures. Taking advantage of these deep domains, we demonstrated second‐harmonic generation without fabricating a channel waveguide.

HVEM Structure Images of Extended 60° - and Screw Dislocations in Silicon

Structure images showing the end-on views of extended 60° - and screw dislocations in silicon crystals are observed with a high voltage electron microscope using the axial illuminating technique. The mean width of 60° dislocations is measured to be 68.7±3.3 A from which the energy of the intrinsic stacking fault is estimated to be 48.7±2.4 mJm-2.

Pyroelectric, dielectric, and piezoelectric properties of LiB3O5

Selected tensor property coefficients of the nonlinear optical crystal LiB3O5 are reported. The full set of pyroelectric, dielectric, and thermal expansion coefficients were measured as a function of temperature. The five independent piezoelectric coefficients, the full set of electromechanical coupling coefficients, along with the compliance constants, were measured at room temperature. The material was found to be quite anisotropic in most property coefficients. The piezoelectric and electromechanical coupling coefficients were reasonably low, and comparisons are made between LiB3O5 and other borate crystals. The material showed strong ionic conductivity along the 〈001〉 direction, with a calculated activation energy for Li transport of 0.43 eV.

Investigation of bulk laser damage threshold of lithium niobate single crystals by Q‐switched pulse laser

Bulk laser damage threshold of 2‐in.‐diam. MgO‐doped LiNbO3 crystals grown using the Czochralski technique has been measured using a Q‐switched Nd3+:LiYF4 laser. The threshold showed dependence on the crystal quality. The highest bulk laser damage threshold (14 J/cm2 at 1.053 μm wavelength with 1‐ns pulse width) was obtained in the LiNbO3 crystal doped with 1 mol % of MgO. The lowering of bulk laser damage threshold was observed in the crystals doped with MgO at more than 3 mol %. These crystals contained the local aggregations of MgO which increased the scattering centers and decreased the transparency.