Z-cut Crystals Research Articles

Ultraviolet light assisted periodic poling of near-stoichiometric, magnesium-doped lithium niobate crystals

Ferroelectric domain reversal by application of electric-fields to near-stoichiometric lithium niobate crystals containing 1.3 mol % magnesium is investigated. The +z-face of the crystal is coated with a patterned photoresist layer that yields both a structured ultraviolet light absorber and a structured electric insulator. Periodic ferroelectric domain inversion in a z-cut crystal is then achieved by combination of illumination with light of the wavelength of 334 nm that reduces the coercive field strength inside the crystal by up to 50% and application of an external electrical field. Domain patterns with a period length of 10 μm are fabricated in a 500 μm thick crystal.

Anisotropy in laser performance of Yb:GdCa_4O(BO_3)_3 crystal

We report distinct laser performance of Yb:GdCa(4)O(BO(3))(3) crystals cut along different principal optical axes using an unpolarized diode pump. The continuous-wave (cw) laser oscillation generated with y-cut crystal is polarized either with E parallel x or with E parallel z depending on the output coupling (T) utilized; a specific T=3% leads to a special situation in which the two orthogonal polarization states coexist oscillating at different wavelengths. The laser oscillation achieved with x- and z-cut crystals is also polarized, but with a fixed polarization of E parallel z and E parallel x, respectively. The most efficient laser operation is obtained with the y-cut crystal, generating a cw output power of 7.35 W at 1083-1085 nm with an optical-to-optical efficiency of 63%, the slope efficiency being as high as 84%.

Off-Congruent LiNbO3 Crystals Prepared by Li-Poor Vapor Transport Equilibration for Integrated Optics

X- and Z-cut off-congruent LiNbO3 (LN) crystals for use for integrated optics were prepared by carrying out Li-poor vapor transport equilibration (VTE) treatment on 1-mm-thick congruent plates at 1100 °C for durations ranging from 65 to 170 h. The Li2O contents and crystalline phase in these Li-poor VTE-treated crystals were characterized by using Raman scattering, optical absorption, and powder X-ray diffraction spectroscopy. The studies of optical absorption in the ultraviolet region show that the Li-poor VTE treatments result in different extents of red-shifts of the optical absorption edges (OAEs), and the amount of the red-shift increases with the prolonged VTE duration. The mean Li2O contents in all VTE samples were evaluated from the measured OAEs. The results show that the VTE-induced reduction of the mean Li2O content can reach as much as ∼1 mol% for both cases of X-cut and Z-cut, and the mean Li2O content and the VTE duration follows the linear relations: cLi = (48.62 ± 0.06) − (0.0052 ± 0.0004)t for the X-cut crystals and cLi = (48.53 ± 0.08) − (0.0063 ± 0.0005)t for the Z-cut crystals. The out-diffusion of Li shows a slight anisotropy. The diffusivity in a Z-cut crystal is slightly larger. The results of visible absorption, Raman scattering, and powder X-ray diffraction show that all the VTE crystals still retain the LiNbO3 phase, consistent with the result predicted from the LiNbO3 phase diagram. The critical VTE duration, longer than which the VTE will induce LiNb3O8 phase in the crystal, is roughly evaluated to be about 577 and 476 h for an X-cut and a Z-cut plate, respectively.

Comparison of laser performance of Yb:YCa4O(BO3)3 crystals cut along the principal optical axes

Efficient high-power continuous-wave laser operation is demonstrated with Yb:YCa4O(BO3)3 crystals cut along the X, Y, and Z principal axes, end pumped by a high-power diode. Highest output powers of 6.3–7.3 W are generated, with slope efficiencies in the range of 73–83%. The standard behavior characterized by fixed linear polarization of the output and decreasing oscillation wavelength when increasing the output coupling was observed only for the X-cut crystal; the Y-cut crystal led to the polarization state changing and coexistence, while the Z-cut crystal resulted in dual-band laser operation with a fixed polarization state.

Basic Study of Threefold Rotatory Symmetric Form Quartz Vibrator for Triaxial Gyrosensor

For the actualization of a monolithic triaxial gyrosensor, we have proposed a threefold rotatory symmetric form vibrator using a quartz crystal Z-cut wafer that can be etched to a complex shape. In the former proposed vibrator, however, an etching residue induces bilateral asymmetry in the detection arms. The asymmetry causes coupling between some vibration modes. Additionally, the former vibrator has a high driving input resistance that makes self oscillation difficult. Therefore, we design a modified vibrator to improve the structural symmetry and decrease the driving input resistance of the original vibrator. The modified vibrator has improved mirror symmetry as well as threefold symmetry, and adopts modified driving beams with through holes. The measurement results of the electrical characteristics of the trial vibrators show that the equivalent resistance of the driving mode of the improved vibrator has been reduced 49-fold compared with that of the conventional one. Consequently, we found that the novel vibrator has a highly symmetric form and a low driving resistance that facilitate self oscillation.

SIMS-depth profile and microstructure studies of Ti-diffused Mg-doped near-stoichiometric lithium niobate waveguide

Ti-diffused planer waveguides have been fabricated on pure and Mg-doped near stoichiometric lithium niobate (SLN). Secondary ion mass spectroscopy method was applied to study the Ti diffusion in 1 mol% Mg-doped Z-cut SLN crystal. 100 nm Ti film has been deposited on LN substrate by e-beam evaporation at room temperature. Diffusion constant value for Mg-doped SLN is lower (1.84×10 −13 cm −2/s) than that of pure SLN. Mg-doped CLN also possesses low diffusion constant value of 1.27×10 −13 cm −2/s due to higher doping concentration of Mg (5 mol%). AFM topographic observation reveals that Mg-doped SLN shows lower surface roughness than Mg-doped CLN. The roughness (peak to valley) of the Ti-diffused Mg:SLN is 20 nm compared to 62 nm for the congruent LN waveguide. These features make Mg:SLN highly attractive for the fabrication of efficient waveguides.

Two-dimensional mapping of electro-optic phase retardation in lithium niobate crystals by digital holography

We demonstrate accurate two-dimensional mapping of the phase retardation induced by the electro-optic effect in lithium niobate crystals. Off-axis digital holography is used to investigate congruent z-cut crystals. The spatially resolved optical path difference is interferometrically measured while a linearly rising voltage ramp is applied to the crystal. This procedure provides information on the uniformity of crystals' electro-optic properties and offers the ability to detect the presence of defects that is of fundamental importance for reliable processing of photonic devices.

Polarization smoothing in a convergent beam

A birefringent wedge in a collimated 351-nm beam provides polarization smoothing at the Omega laser facility and provided it for the Nova laser. At the National Ignition Facility, the best place to put such an optic is after the final focus lens. In a converging beam, a flat birefringent plate can closely mimic the polarization-smoothing action of a wedge. In this new design the flat plate is nearly a Z-cut crystal; for the wedges, the optical axis of the crystal lies far from the plate normal.

Continuous index of refraction measurements to 20 GPa in Z-cut sapphire

Isentropic compression experiments (ICE) on Sandia National Laboratories’ Z Accelerator are used to make continuous measurements of the index of refraction in single crystal Z-cut sapphire as the longitudinal stress is gradually increased to 20 GPa (uniaxial strain of about ∼3.9%). A planar, ramp compression wave, generated by a large magnetic field, propagates through a planar copper base plate. Part of the rear surface of the base plate is a free surface and part is covered with a sapphire window. Comparisons are made of velocity histories measured simultaneously at the free surface and at the copper/sapphire interface using a velocity interferometer system for any reflector (VISAR). This is sufficient to determine the index of refraction of the sapphire continuously as a function of density. Perturbations to the compression waves caused by interactions with the free surface and with the sapphire are accounted for by backward or forward solutions to the equations of motion. The effect of the unsteady nature of the compression wave in sapphire on the interferometry measurements is also taken into account. Results validate the interpretation of VISAR measurements on continuous loading experiments performed with optical windows. The measured index of refraction of sapphire agrees with previous studies validating this experimental technique and showing that it is useful for studying other materials for which index of refraction data do not exist. In addition, measured compression isentropes for copper and sapphire compare favorably with existing theoretical models.

Growth and Dielectric Characterization of Large Single Crystals of GaAsO4, a Novel Piezoelectric Material.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Evaluation of acoustic physical constants of LiNbO3 at hypersonic frequencies

The velocity angular dispersion of bulk acoustic modes propagating parallel to the surfaces of X-, Y- and Z-cut crystal plates of LiNbO3 has been measured by Brillouin scattering. The elastic and piezoelectric stress constants of LiNbO3 at hypersonic frequencies, determined from a simultaneous fit to data from the three crystal cuts, are found to be only marginally more accurate than those based on only the X-cut data. Calculations based on the constants fitted to the X-cut data alone predicted accurately the velocity angular dispersion of the surface Rayleigh wave measured simultaneously. The first leaky surface wave on the Z-cut crystal is also experimentally observed whose velocity angular dispersion agrees with the theoretical dispersion computed from the fitted constants. Evidence of dispersion between ultrasonic and hypersonic velocities is found for both surface and bulk acoustic waves.

Growth and dielectric characterization of large single crystals of GaAsO 4, a novel piezoelectric material

Gallium arsenate (GaAsO 4) is a new α-quartz-type piezoelectric material. Large single crystals (8 mm along the c-direction) were grown for the first time by hydrothermal methods. The different crystal faces were indexed by X-ray diffraction. The crystal quality was characterized by infrared measurements. X- and Z-cut crystals were prepared in order to perform dielectric measurements. The dielectric constants of GaAsO 4 ( ε′ 11=8.5, ε′ 33=8.6) are the highest found among α-quartz type materials. A linear relationship has been established between a structural property, the tetrahedral tilt angle δ, and the dielectric constants for the well-known α-quartz homeotypes. These results indicate that gallium arsenate should have the highest piezoelectric coupling coefficient of any material of this family.

Combined x-ray imaging and diffraction study of light-induceddistortions in Fe:LiNbO3

A real-time investigation of the light-induced deformation on Fe:LiNbO3crystals was performed by taking advantage of both the highflux and the detector system (FRELON CCD camera) available at a modernsynchrotron radiation source like the ESRF. The observed contrast andeffective misorientation after illumination of a Z-cut crystal are mainlydue to (00l) lattice planes tilts. Considering the coupling of the bulkphotovoltaic field and the converse piezoelectric effect, we develop a`parallel plate condenser'-like macroscopic model of the distortion generatedby the visible light beam. Calculation of the effective misorientation at theedges of the illuminated region gives values of the order of ±20 arcsec which are consistent with our experimental data.}\\setlength\\abswidth{32pc

Second harmonic generation in reverse proton exchanged Lithium Niobate waveguides

We investigate efficient second harmonic generation in reverse proton exchanged Lithium Niobate waveguides. In z-cut crystals, the resulting buried and surface guides support TM and TE polarizations, respectively, and are coupled through the d 31 nonlinear element. Numerically estimated conversion efficiencies in planar structures operating at 1.32microm reach 90% in 2cm or a normalized 14% microm/Wcm.

Anisotropy of sound velocity for a new PbB 4 O 7 crystal as determined by the laser ultrasonic technique

O7 crystal is a new nonlinear optical crystal. For the first time the anisotropy of the velocities of its longitudinal and surface acoustic waves (SAWs) are determined by laser ultrasonic technique. The velocities of surface waves for X-, Y-, and Z-cut crystals are also calculated. The theoretical calculations of slowness curves are in good agreement with experimental results. The SAW slowness curve is elliptical for Y- or Z-cut crystal wafers, and circular for an X-cut wafer.

New long-lived memory effects in LiNbO3 crystals

This paper describes a new way of recording information by changing the potential contour at the surface of z-cut crystals of LiNbO3. The effect of various kinds of external perturbations on the rate of decay of optical images written using this method is investigated, along with the possibility of writing information on crystals with transition-metal impurities.

Bound electronic Kerr effect and self-focusing induced damage in second-harmonic-generation crystals

We present an investigation of third-order electronic nonlinearities in second-harmonic-generation (SHG) crystals using a picosecond 532 nm wavelength beam. The crystals studied include KTP, KTA, BBO, LBO and LiNbO 3. Using the Z-scan technique the nonlinear refractive indexes and two-photon absorption coefficients in the z-cut crystals are measured, as well as in KTP, BBO and LBO along the phase-matching angles for the SHG of 1064 nm radiation. The microscopic origin of the measured refractive nonlinearity can be understood in terms of bound electronic effects, and the theoretical predictions are in agreement with our measurements. Finally, we perform an experimental study on the self-focusing induced damage in these crystals by extending the Z-scan method. The measured damage threshold is inversely proportional to the nonlinear refractive index and the thickness of a crystal.

Phase-matched second-harmonic generation at 789.5 nm in a GaSe crystal

Phase-matched second-harmonic generation in the highly χ(2)-active layered semiconductor GaSe is demonstrated in the near-infrared frequency region. Due to the high indices of refraction, the internal phase-matching angle of about 30° is beyond the critical angle of total reflection for a z-cut crystal. This problem is overcome by sandwiching the crystal between two half-cylindrical glass rods, which leads to a shift of the critical angle to larger values.

Correlation of substitutional hydrogen to refractive index profiles in annealed proton-exchanged Z- and X-cut LiNbO3

Previous disagreements concerning a linear correlation between the hydrogen (H) concentration and the extraordinary refractive index ne in proton-exchanged lithium niobate (LiNbO3) have been resolved by partitioning the total H into optically active substitutional H and optically inactive interstitial H. The H and Li spatial variations in both Z- and X-cut crystals were determined by secondary-ion-mass spectrometry (SIMS) with a quantitative evaluation in atoms/cm3. These samples were proton exchanged in neat benzoic acid at 185 °C and then were annealed at 400 °C for times t from 6 to 240 min in wet flowing oxygen. For the Z-cut crystals, fit of the SIMS measured H profiles by expressions obtained from the diffusion equation for diffusion from a finite layer gave a substitutional H diffusivity of DZs=5.0±0.3×10−12 cm2/s and an interstitial H diffusivity of DZi=1.4±0.1×10−11 cm2/s. The wet flowing oxygen acts as a constant source of interstitial H at the surface with the diffusivity DZi and gives an integrated H concentration due to the flowing wet oxygen which increases as √t. The Li diffusivity was DLiZ=4.8±0.2×10−12 cm2/s which is nearly equal to DZs. For X-cut crystals, the substitutional H diffusivity was DXs=3.4±0.2×10−12 cm2/s and the interstitial diffusivity was DXi=1.3±0.2×10−11 cm2/s. The ne profiles were evaluated by means of optical prism-coupling measurements and numerical simulations. In both cases of crystal orientation, the effective index diffusivity is nearly equal to the diffusivity of substitutional H. Furthermore, there is an excellent linear relationship between the ne profile and the corresponding substitutional H distribution.

Optical transmission properties of LiTaO3crystals

Abstract Optical transmissions of z-cut and x-cut ferroelectric LiTaO3 single crystals are measured from 200 nm to 25 μm. The optical properties of poled and annealed samples are compared and discussed respectively.