Potassium Niobate Crystal Research Articles

Thermal fixing of volume holograms in potassium niobate

Volume holograms are thermally fixed in a pure and an iron doped potassium niobate crystal through the screening of a photorefractive space-charge field by a nonphotoactive species at elevated temperature (110 °C). The nonphotoactive species is identified as the hydrogen ion. Fixed holograms are reconstructed at different temperatures. A diffraction efficiency of 16% in a 6 mm thick KNbO3:Fe sample is measured. The time constant and activation energy associated with the thermal induced decay of the hologram are determined to be 2.9×10−7 s and 0.81 eV for the KNbO3:Fe sample, and 1.35×10−7 s and 0.79 eV for the pure KNbO3 sample.

Near-infrared performance of photorefractive nickel-doped KNbO_3 crystals

Nickel-doped potassium niobate crystals show strong photorefraction in the near-infrared wavelengths from 700 to 800 nm. Two-wave mixing gain coefficients as high as 9 cm-1 are obtained with the c-face entrance geometry. A very long dark decay time (>1 year) is observed in this wavelength range, which is of interest for optical storage applications that use diode lasers. Self-pumped phase conjugation is realized. The reflectivity takes values from 32% at 700 nm to 6% at 800 nm. These are the longest wavelengths at which the self-pumped phase conjugation has been observed in KNbO3 at room-temperature operation.

Infrared photorefractive effect in doped KNbO_3 crystals

The photorefractive sensitivity of potassium niobate crystals doped with Ce, Co, Cu, Fe, Mn, Ni, and Rh and double-doped with Mn and Rh is investigated over an extended spectral range. We present experimental evidence on extrinsic properties important for the photorefractive effect, such as absorption and effective trap density. Photorefractive gratings are investigated with two-wave mixing experiments. Results on exponential gain, response time, and photorefractive sensitivity at near-infrared wavelengths are reported. The best photorefractive sensitivities at 860 and 1064 nm were obtained in crystals doped with Rh, Fe, Mn, and Mn–Rh. This makes them suitable for applications at laser-diode wavelengths; at 1064 nm, however, Rh:KNbO3 shows a better photorefractive sensitivity than the others.

Light-induced charge transport properties of potassium niobate crystals doped with nickel

Measurements of absorption, light-induced absorption changes, photoconductivity, and bulk photovoltaic currents are carried out for different light wavelengths and intensities with a potassium niobate crystal (KNbO3) containing 90 mol ppm Ni. Absorption bands around 2.1 and 2.7 eV are present. The band around 2.1 eV yields no significant contribution to the photoconductivity but causes appreciable bulk photovoltaic currents. The photoconductivity is larger than in KNbO3:Fe which makes KNbO3:Ni promising for holographic applications. A nonlinear intensity dependence of the photoconductivity and of the bulk photovoltaic current density indicates that more than one photorefractive level contribute to the charge transport processes. The bulk photovoltaic currents are negligible in usual holographic experiments.

Growth and characterization of pure, and doped crystals of potassium niobate

Four compositions of potassium niobate single crystals with 0 wt% Sm (KN), 1 wt% Sm (KND-1), 2 wt% Sm (KND-2) and 1 wt% Sm + 1 wt% Sn (KND-3) were grown by controlled colling of the melt. In powder X-ray diffraction investigations, it is shown that doping has decreased lattice parameter b 0 values except for KND-1 retaining an orthorhombic nature and has increased tetragonality in the crystals. SEM study revealed that with increasing percentage doping, the grain size had increased. Growth habits are significantly influenced and modified due to doping. The layered growth of KN shows a needle-shaped growth habit with a rectangular cross section in KND-1. This change is more predominant in KND-3 and is insignificant in KND-2. It appears that impurities influence the kinetics of nucleation and growth.

Effects of meniscus on the directional growth of potassium niobate single crystals

The study of meniscus effects on the directional growth of single crystals of potassium niobate (KNbO 3) with a [110] pc oriented seed by the top-seeded-solution-growth technique has been described. The directional growth of KNbO 3 single crystals has been illustrated for different crystallographic orientations of the crystal. Experimental results show that the shape of the solution flux meniscus, which is determined by a number of growth parameters, has a significant effect on growth rates on different 100 pc, 010 pc and 001 pc type surfaces. Findings based on this work enable one to select a dominant growth direction and hence to engineer the geometrical shaping of resultant KNbO 3 single crystals through careful control of growth parameters. Maximum crystal dimensions for the grown KNbO 3 along [100] pc and [001] pc achieved in this work are 34.0 and 31.2 mm, respectively.

Compact 10 mW all-solid-state 491 nm laser based on frequency doubling a master oscillator power amplifier laser diode

We report on continuous-wave blue-green light generation by direct frequency doubling a monolithically integrated master oscillator power amplifier laser diode in a potassium niobate (KNbO 3) crystal. 10 mW of diffraction limited ( M 2 ≤ 1.1) second-harmonic light at 491 nm is generated with a fundamental power of 760 mW incident on a 17 mm long crystal. The blue-green laser radiation is 100% polarised and single-longitudinal mode with a frequency linewidth of ∼33 GHz corresponding to a coherence length of ∼6 mm. The root-mean-square fluctuations of the second-harmonic output power is as low as 0.1% and the power drift is less than 3% over six hours.

Tunable blue light generation by sum-frequency mixing of AlGaAs and InGaAs laser diodes in KNbO3

A 25 mW continuous-wave blue laser is demonstrated by noncritical type I phase-matched sum-frequency mixing of a master-oscillator power-amplifier InGaAs laser diode and an AlGaAs laser diode in a potassium niobate (KNbO3) crystal. The blue laser is continuously tunable over the wavelength range from 431 to 438 nm.

Temperature variation of the refractive index of potassium niobate

Use was made of a novel Fabry–Pérot interferometer technique to determine the variation of refractive index with temperature (∂n/∂T) of a potassium niobate crystal with a GaAlAs diode laser. The transverse intensity distributions of the laser transmitted through the crystal were found to be temperature dependent, and the ∂n/∂T values along crystallographic b and c axes were determined to be −4.5×10−5 and 6.1×10−5 °C−1, respectively. The temperature changes required for tangential tuning from transverse mode TEMqmn to TEMqm+1n and sagittal tuning from TEMqmn to TEMqmn+1 were found to be 0.29 and 1.27 °C, respectively, when the laser was polarized along the b axis. When the laser polarization was along the c axis, the tangential and sagittal tunings were found to be 0.10 and 0.54 °C, respectively. These differences between the tangential and sagittal directions indicated that the monolithic ring resonator used was indeed asymmetric.

Mirrorless self-pumped phase conjugation in KNbO_3:Mn and KNbO_3:Co

Self-pumped phase conjugation is experimentally studied in the usual 0 degrees -cut potassium niobate crystals doped with either manganese or cobalt. Phase-conjugate reflectivities as high as 52% and 32% are obtained for these two kinds of crystal in the mirrorless cat configuration at 488 nm. The influence of experimental conditions, such as the incidence angle, the incident position, and the incident intensity, on phase conjugation are studied.

Dispersion of thermo-optic coefficients in a potassium niobate nonlinear crystal

The thermo-optic coefficients, i.e., the variation of refractive index with temperature (dn/dT) for potassium niobate crystal, KNbO3, are analyzed critically by use of a physically meaningful model. This model is based on the thermal expansion coefficient, and the optical band gaps, such as excitonic and isentropic instead of the consideration of the spontaneous polarization as suggested earlier. The computed optical constants have been used to calculate refractive indices for any wavelength from 0.4 to 3.4 μm at any operating temperature within orthorhombic phase accurately.

Electro-and acousto-optic properties of KNbO3crystals

Abstract The complete set of elastic, piezoelectric, dielectric, elasto-optic, and electrooptic tensors of potassium niobate crystals was determined by numerically evaluating the measurements published before and the additional measurements performed recently in our laboratory. Improvements in the accuracy of experimental data could be obtained because of the improved optical quality and larger size of KNbO3 crystal samples that are available nowadays. To illustrate the benefits of the newly determined complete set we calculate effective electro-optic coefficients and dielectric constants of KNbO3 in photorefractive experiments, where the elastic deformations associated with a periodic space-charge field have to be considered.

Photorefractive-crystal shape-parameter influence on formation of self-pumped phase conjugation

The influence of crystal-shape parameters on formation of self-pumped phase conjugation is studied experimentally. The parallelism of two c-cut faces of a barium strontium potassium niobate crystal of cuboid shape is changed to control the internal oscillation and thus to induce or to suppress the generation of self-pumped phase conjugation.

Analysis of the electro‐optic effect in anisotropic crystals with 2‐mm AND 3‐m point group symmetry using a first‐order perturbation technique

AbstractThe results of a recently proposed perturbation approach are successfully applied to the analysis of the Pockels effect in some representative electro‐optic crystals, namely, potassium niobate and lithium niobate crystals. © 1993 John Wiley & Sons, Inc.

Second harmonic generation at 972 nm using a distributed Bragg reflection semiconductor laser

We have doubled the frequency of a single mode distributed Bragg reflection (DBR) semiconductor laser. The laser is optically locked to an external enhancement ring resonator that contains an antireflection coated potassium niobate crystal. Unlike Fabry–Perot cavity lasers the DBR laser is found to operate in only one longitudinal mode and allows stable second harmonic generation. We present the results obtained with a singly and doubly resonant cavity. A total output of 1.2 mW tunable single mode radiation near 486 nm has been generated from a laser output power of 25 mW at 972 nm without the use of optical isolators or active feedback control.

Frequency-doubled and Q-switched 946-nm Nd:YAG laser pumped by a diode-laser array

A Q-switched 946-nm Neodymium:yttrium aluminum garnet (Nd:YAG) laser pumped by a diode-laser array has been developed. At room temperature, pulses with 4.9-microj energy and 68.5-ns pulse duration were observed. When the temperature of the Nd:YAG crystal was lowered to 5 degrees C, the duration of the pulses was reduced to 62 ns, giving rise to peak powers of 76 W. By focusing the Q-switched pulses into a 5-mm-long potassium niobate crystal, second-harmonic generation produced blue light pulses at 473 nm of 42-ns duration and 22-W peak power. The pulse repetition rate was kept at 1.5 kHz throughout.

Holographic experiments in perovskite materials

Abstract Holographic diffraction efficiency, photo-and dark-conductivity of a nominally pure potassium niobate (KNbO3) crystal are investigated. An unusual dark decay of holographic gratings is observed and discussed in view of the photorefractive process.

432-nm source based on efficient second-harmonic generation of GaAlAs diode-laser radiation in a self-locking external resonant cavity

Using a potassium niobate crystal in a modified self-locking power-buildup cavity, we have frequency doubled the 865-nm output from a GaAlAs laser diode. With 12.4 mW of input power we have obtained a unidirectional output of 0.215 mW at 432 nm. In contrast to previous diode doubling experiments, the output was both single frequency and circular Gaussian. With better optics, substantially higher conversion efficiencies should be possible using this technique.

Potassium niobate optical parametric oscillator pumped by the second harmonic of a garnet laser

An experimental investigation was made of a KNbO3 crystal as a nonlinear element of an optical parametric oscillator (OPO). A tuning range of 0.86–1.4 μ and a conversion efficiency higher than 5% were achieved. Experimental investigations were made of the 2ω phase-matching angles and temperatures for various pump wavelengths, of the optical quality of the crystals and their optical damage threshold, and of the parameters of growth and conversion of potassium niobate crystals to the single-domain state. The output characteristics of a potassium niobate OPO were compared with those of lithium and barium sodium niobate OPO's.

Photovoltaic effect and photoconductivity in reduced potassium niobate crystals

Photovoltaic effect and photoconductivity in reduced potassium niobate crystals