Qingcai Guan

Growth and characterization of cubic KTa1-xNbxO3 crystals

Abstract The top-seeded flux method was used to grow large size and good quality undoped, Cu or Fe doped cubic phase KTa 1- x Nb x O 3 crystals. The morphology, homogeneity, dielectric properties and electrooptic properties of these crystals have been investigated. The photorefractive properties of a Cu-doped KTN crystal have also been studied and the results obtained show that the diffraction efficiency of this crystal is above 50% at room temperature.

Self‐pumped phase conjugation with a new mechanism in KTa1−xNbxO3:Fe crystals

A new model is proposed to explain the origin of the self‐pumped phase conjugation (SPPC) that we have observed in KTa1−xNbxO3:Fe crystals. In this model SPPC is generated by both four‐wave mixing and backscattering processes rather than by only one of them. The advantage of this kind of phase conjugator is also discussed.

PHOTOREFRACTIVE PROPERTIES AND SELF-PUMPED PHASE CONJUGATION OF TETRAGONAL FE-DOPED KTA1-XNBXO3 CRYSTAL

This letter reports the two‐wave mixing experimental results of tetragonal Fe‐doped KTa1−xNbxO3. A 7.3 cm−1 gain coefficient and 42% diffraction efficiency have been obtained. For the first time internally self‐pumped phase conjugation is being observed in this crystal. At room temperature, the conjugate reflectivity measured is 21%.

Optical properties of NdxGd1−xAl3(BO3)4 crystal

The optical properties of NdxGd1-xAl3(BO3)4(NGAB) crystal are reported. The refractive index of it were mesured by V-prism method. The absorption spectra and the flourescence specra of NGAB were also obtained. The optical parameters of NGAB were calculated following J-O theory, the three optical parameters are Ω2 = 1.805 × 10−20, Ω4 = 1.85 × 10−20, Ω6 = 3.793 × 10−20(RMS= 1.4 × 10−7) and βc(4F3/2 →4I11/2) is about 0.53.

High reflectivity self‐pumped phase conjugation in an unusually cut Fe‐doped KTa1−xNbxO3 crystal

In this letter, a new type of self‐pumped phase conjugation (SPPC) is demonstrated and a phase conjugate reflectivity as high as 83.8% is measured in an unusually cut Fe‐doped KTa1−xNbxO3 (KTN:Fe) crystal with a He‐Ne laser. Some novel characteristics of this type of device are found, which may reduce the need for special crystal qualities to obtain SPPC. Finally, a possible mechanism is postulated to reasonably explain this type of SPPC.

Influences of iron doping on the photorefractive properties of KTa1−xNbxO3 crystals

The influences of iron doping on the photorefractive properties of KTa1−xNaxO3 (KTN) crystals were studied. The two‐wave‐mixing gain coefficients and the grating formation rates were measured in undoped and Fe‐doped KTN samples. Photorefractive parameters, such as the effective carrier number density, were determined for these samples. It was shown that the gain coefficient increases significantly with the doped Fe content, but the grating formation rate decreases with it, and that all the influences of iron doping originate mainly from the variation of the effective carrier number density.

Self-pumped phase conjugation with high reflectivity by stimulated forward- and backward-scattering tetragonal potassium tantalate niobate crystal

Abstract Self-pumped phase conjugation in tetragonal Fe-doped KTa 1− x Nb x O 3 crystal with a Q -switched, frequency-doubled Nd:YAG laser with power in the milliwatt range is demonstrated. A phase conjugate reflectivity as high as 55% was measured. Both stimulated forward- and backward-scattering were involved in the self-pumping process simultaneously. The coupling characteristics of this crystal are analyzed and compared with those of BaTiO 3 crystal.

Mechanism transition of self-pumped phase conjugation in KTa1 −xNbxO3:Fe crystals

Mechanism transitions of Self-Pumped Phase Conjugation (SPPC) with wavelength and doping concentration are observed in KTN:Fe (KTa1 −xNbxO3:Fe withx = 0.48) crystals. The SPPC mechanism in KTN: Fe (0.4 wt. %) crystal transforms from “Stimulated Photorefractive Backscattering and Four-Wave Mixing” (SPB-FWM) to “cat” (or total internal reflection) as the wavelength increases from 514.5 nm to 620 nm. SPPC at 514.5 nm is formed with the “cat” mechanism in a 0.2 wt. % doped KTN:Fe crystal, while with the SPB-FWM mechanism in a 0.4 wt. % doped one. These mechanism transitions are discussed with respect to the dependence of the backscattering gain coefficient of the crystals on wavelength and doping concentration.

Growth defects in flux grown RbTiOAsO4 crystals observed with white-beam synchrotron radiation topography

Abstract The growth defects in flux grown RbTiOAsO 4 crystal have been investigated by white-beam synchrotron radiation topography. It is found that growth sector boundaries are the primary growth defects and they show strong X-ray kinematical contrast in the topograph. All the dislocations are growth induced and appear only in the near capping region. The area away from the capping region is nearly dislocation free. Growth bands show weak contrast in the X-ray topograph, which implies that the impurity contents are relatively low in various growth sectors and each growth sector is uniform in composition.

Asymmetric transmission device using Fe-doped KTaxNb 1–x O 3 crystal

A new type of asymmetric optical transmission device based on contradirectional two-wave mixing between an incident beam and its backward-scattering beams in Fe-doped KTa(x)Nb(1-x)O(3) crystal is demonstrated. The transmittance ratio of the beams propagating in opposite directions can be adjusted by a change in the angle between the incident beam and the c axis; the maximum ratio is nearly 50:1 at only one incident beam. Approximate solutions of two opposite transmittances are derived and discussed. It is possible to use this device as an optical isolator or an optical diode.