Chen Huanchu

Studies on the growth and defects of GdCa4O(BO3)3 crystals

Abstract New nonlinear optical crystals GdCa4O(BO3)3 grown by the Czochralski method in a platinum crucible under air atmosphere are reported in this paper. The growth mechanism is a typical two-dimensional nucleation layer growth. The twin and inclusion defects of this crystal are observed using optical microscopy. The incidence of twinning is in good agreement with Hurles model. The approaches to reduce and eliminate the defects are presented.

Anisotropy of Nonlinear-Optical Property of RCOB ( R = Gd, Y) Crystal

The nonlinear-optical coefficients of RCOB (R = Gd, Y) crystals are measured. The spatial distribution of deff (effective nonlinear-optical coefficient) is subsequently determined. Our experiments show that the maximum deff occurs at the second quadrant. The second-harmonic generation efficiency reaches 48% for a 6 mm long, (113.2°, 47.4°)-cut GdCOB, and 41.5% for a 5mm long, (113°, 36.5°)-cut YCOB, respectively. The intracavity frequency doubling of GdCOB is reported for the first time.

Optical Properties and Linear Electro-Optic Effect in Ferroelectric Single Crystal KNSBN

The experiments for optical and linear electro-optic properties in tungsten-bronze type ferroelectic single crystal KNSBN [(KxNa1-x)0.4(SryBa1-y)0.8Nb2O6 with 0.5<x<0.75, 0.30<y<0.90] are described. This crystal has large birefringence with transparency range from 4000 A to 5.6 µm. The refractive indices n0 and ne of 2.3358 and 2.2747 at 5610 A are given. The low half-wave voltage in KNSBN gives the high value n03rc of 730×10-12 m/V, which is figure of merit for EO modulator materials. The thershold energy of 618 MW/cm2 (4pps) for laser damage makes KNSBN attractive for large power laser modulation.

Single crystal growth and determination of physical properties of (K1−xNax)0.4(Sr1−yBay)0.8Nb206

Abstract The typical conditions of growth of the ferroelectric single crystal series of KNSBN were described. The date of lattics parameter, dielectric, pyroelectric, elastic, and piezoelectric constants have been measured.

Raman spectra of KNSBN crystals at the ferroelectric-paraelectric phase transition

Abstract Raman spectra of KNSBN single crystals with different compositional ratios of Sr/Ba and K/Na have been measured. The limited softening of a lattice mode v 2 and the gradual disappearance of another lattice mode v 4 are verified as the most important features related to the ferroelectric-paraelectric phase transition in this system.

Quantitative studies of solute boundary layers around crystals by holographic phase-contrast interferometric microphotography

Abstract This paper discusses an effective real-time measuring technique - holographic phase-contrast interferometric microphotography - for the studies of solute boundary layers around a crystal and the essential conditions for precise measurements under complicated conditions. The experiments demonstrated that the thickness of the solute boundary layer increased linearly with increasing supersaturation in the free-convection state while the solute distribution within the boundary layer exhibited nonlinear variations.

Phase transitions and determination of dielectric, elastic and piezoelectric constants in the ferroelectric single cyrstals PBN and Li, Na-doped PBN

Abstract Two ferroelectric single crystals, Pb0.37Ba0.63Nb2O6 and Pb0.30Ba0.533Na0.306Li0.028Nb2O6, which were pulled from the melt by the Czochralski technique, were studied. It was determined by x-ray diffraction that both crystals have a tetragonal point group 4 mm. The lattice parameters at room temperature are a = 12.493 A and c = 3.984 A for PBN, and a = 12.493 A and c = 3.970 A for Li, Na-doped PBN. The Curie point Tc designating the ferroelectric to paraelectric phase transition was determined from the peak of the permittivities for the two crystals. All of the dielectric, elastic and piezoelectric constants were measured. The results showed that PBN possesses strong piezoelectricity with a d 15 of 108 × 10−12 C/N. This crystal should be a suitable material for piezoelectric transducers working in the shear mode and for surface acoustic wave (SAW) devices.

Self-pumped phase conjugation in (K0.5Na0.5)2y (Sr0.61Ba0.39)1-yNb2O6 at 633nm

Self-pumped phase conjugation has been observed in Ce-doped (K0.5Nb0.5)2y (Sr0.61Ba0.39)1-yNb2O6 (KNSBN) crystal at 633nm by using He-Ne laser. The phase conjugate reflectivity as high as 40% was measured. The reflectivity as function of incident angles and the relation of response time to the incident intensities were studied experimentally.

Crystal growth of high Tc superconductors YBa2Cu3Ox, Bi3Sr3CaCu2.5Ox and Pb0.6Bi3Sr2CaCu3Ox

Single crystals of YBa 2 Cu 3 O x , Bi 3 Sr 3 CaCu 2.5 O x and Pb 0.6 Bi 3 Sr 2 CaCu 3 O x have been grown by the flux method. The crystals obtained have sizes varying from 2.5 x 2.0 x 0.1 mm 3 to 10 x 4 x 3 mm 3 . These crystals have an orthorhombic structure with cell parameters a = 3.838(1) A, b = 3.871(1) A and c =11.738(4) A (YBa 2 Cu 3 Ox); a = 5.39 X, b = 5.37 A and c = 31.01 A (Bi 3 Sr 3 CaCu 2.5 Ox); and a = 5.38 A, b = 5.34 A, c = 30.55 A (Pb 0.6 Bi 3 Sr 2 CaCu 3 Ox). Measurements of resistivity and AC susceptibility confirmed that these crystals are bulk superconductors with T c (zero) of 91.4, 90 and 82 K, respectively. Differential thermal analysis (DTA) measurements were made to study the crystal growth process and thermal properties of these crystals.

The range profile of Hg+ in Li0.16Na0.84NbO3

The range profile of Hg+ implanted in Li0.16Na0.84NbO3 at energies from 50 to 350 keV is measured by MeV 4He+ Rutherford back-scattering. A computer program based on the Biersack model has been written to facilitate comparison with the experimental results. It is found that the measured projected range is in good agreement with the calculated value and a marked improvement in the range straggling is obtained when the second-order energy loss is taken into consideration.