Baichang Wu

Computer‐Assisted Search for Nonlinear Optical Crystals

Based on anionic group theory, a computer-assisted material design system (CAMDS) has been developed. This method has proved to be a highly efficient means of discovering nonlinear optical crystals. In this method, important optical properties of the target compounds (borates, for example), such as the dij coefficients, refractive indices, and energy bandgap, are calculated so that a prior evaluation can be made before experiments. The results have given a meaningful guide to ensuing experiments, which have led to our discoveries of KBBF (KBe2BO3F2) and SBBO (Sr2Be2B2O7) in the past several years, followed by other members of the SBBO family in recent years. On the other hand, this system can also be used to evaluate the dij coefficients of the borate nonlinear optical (NLO) crystals discovered recently whose dij coefficients have not been determined experimentally.

Linear and nonlinear optical properties of the KBe2BO3F2 (KBBF) crystal

Studies of the linear and nonlinear optical properties of KBBF crystal were carried out. The Sellmeiers equations, which are accurate from 1.4 μm to about 180 nm, are reported. KBBF crystal has been found to be phase matchable for second harmonic generation down to 180 nm and to possess a phase-matching retrace behavior, which just occurred in the commercial laser region.

The vacuum ultraviolet phase‐matching characteristics of nonlinear optical KBe2BO3F2 crystal

The nonlinear optical crystal KBe2BO3F2 has been used to produce vacuum ultraviolet second‐harmonic generation with an output range of 200–184.7 nm. The Sellmeier equation further indicates that this new crystal can generate the sixth harmonic from Nd‐based laser systems.

New development of nonlinear optical crystals for the ultraviolet region with molecular engineering approach

Potassium fluoroboratoberyllate KBe2BO3F2 (KBBF) has been revealed theoretically and experimentally as a novel ultraviolet nonlinear optical crystal, but it is found to be very difficult to grow in a large size, because of the weak binding interaction between the (Be2BO3)∞ units, which leads to an apparent layer habit in the growth. By using a molecular engineering approach, oxygen bridges when brought in to strengthen the binding between the infinite units are found to be useful to overcome the above shortcoming of KBBF, and in the light of it another new ultraviolet nonlinear optical crystal—strontium boratoberyllate Sr2Be2B2O7 (SBBO) has been discovered. The linear optical properties of SBBO are similar to KBBF’s, but its nonlinear optical properties are better than that of the latter. d22(SBBO)≂d22(β‐BaB2O4), which is two times higher than d11 of KBBF. SBBO has very good mechanical properties, and it is also not deliquescent. So SBBO is expected to have great potential for the application in ultraviol...

Searching for new nonlinear optical materials on the basis of the anionic group theory

Based on the anionic group theory of nonlinear optical crystals and the relationship between the microscopic nonlinear coefficients of the anionic group and the macroscopic coefficients of the crystal, an evaluation system has been established to analyze the spatial arrangement of the anionic groups in a crystal lattice. A structural criterion is given to find which crystal has a favorable spatial arrangement of the anionic groups in terms of its nonlinear effects. Some of the currently available nonlinear optical crystals have been analyzed in this way with a computer program to test the evaluation method, and results demonstrate that the above structural criterion is quite reliable. Several compounds with crystallographic data from an inorganic crystal structure database were evaluated and found to be possible good candidates for nonlinear applications.

New nonlinear optical crystal K 2 Al 2 B 2 O 7

The new nonlinear optical crystal K2Al2B2O7 is discovered with the molecular engineering approach on the basis of anionic group theory. An optically perfect single crystal with space group P321, free of moisture and hygroscopy, is readily grown by the top-seeding flux method. Its transparence range covers 180 to 3600 nm. The refractive indices are measured with the minimum-deviation method, based on which the Sellmeier equation is obtained. The measured nonlinear optical coefficient d11 is 0.45 pm/V. The moderate walk-off angle and angular bandwidth, together with the high optical homogeneity, make it a promising candidate for the fourth- and the fifth-harmonic generation of a Nd:YAG laser.

Phase‐matching retracing behavior: New features in LiB3O5

Retraces of phase‐matching (PM) angles and noncritical phase‐matching temperatures for both type I and type II second harmonic generation in LiB3O5(LBO) are first demonstrated. By fitting to the measured PM angles at room temperature, new Sellmeier’s equations of LBO are obtained. Further analyzing the spectral and angle acceptances, we point out that LBO is particularly useful in doubling radiations near 1.3 μm such as 1.32 μm of Nd:YAG, 1.31 μm of Nd:YLF, and 1.34 μm of Nd:YAP.

Red–green–blue generation from a lone dual-wavelength GdAl3(BO3)4:Nd3+ laser

We demonstrate the simultaneous generation of the three basal red–green–blue colors from a lone GdAl3(BO3)4:Nd3+ bi-functional laser and optical nonlinear crystal. The laser works in a dual-wavelength operation in the two 4F3/2→4I11/2 (near 1062 nm) and 4F3/2→4I13/2 (near 1338 nm) channels, under a fixed wavelength pumping (at 744.7 nm) and with a fixed crystal orientation. Red and green results from self-frequency doubling of the two laser channels, blue results of self-sum frequency mixing of the pump and the 1338 nm laser.

Self-frequency tripling from two cascaded second-order nonlinearities in GdAl3(BO3)4:Nd3+

We combine inside a single noncentrosymmetric laser crystal, GdAl3(BO3)4:Nd3+, a stimulated emission and two second-order nonlinearities in cascade. The first one self-doubles the 1062.8 nm Nd3+ laser emission corresponding to the 4F3/2→4I11/2 channel, despite the fact that it is not phase-matched. The second one can be phase-matched or not and mixes the laser wave and its second harmonic (SH) in order to produce the third harmonic (TH) at 354.3 nm.

Spectroscopic properties of Er3+ transitions in SrWO4 crystal

Er3+:SrWO4 crystal of good optical quality was grown by Czochralski technique method. Polarized absorption and emission spectra of Er3+ ions in SrWO4 crystal have been investigated. The Judd-Ofelt (JO) theory was applied to the polarized absorption spectra of Er3+:SrWO4 to obtain the three JO parameters: Ω2=7.41×10−20cm2, Ω4=0.25×10−20cm2, and Ω6=1.71×10−20cm2. The radiative probabilities, radiative lifetimes, and branch ratios of Er3+:SrWO4 were calculated. The stimulated emission cross sections of the potential laser transitions at 1535nm were determined using the reciprocity method and the Fuchtbauer-Ladenberg formula, and the potential laser gain versus wavelength for the I13∕24→I15∕24 transition has been estimated and discussed.