KDP Single Crystals Research Articles

The pH effects on the growth rate of KDP (KH2PO4) crystal by investigating Raman active lattice modes

AbstractWe report on the dependence of the pH value on the growth rates of KDP single crystals. Extensive experimental work has been carried out in order to find the optimum pH ranges for growing KDP single crystals with suitable sizes and high optical quality. Different techniques including micro‐Raman back‐scattering spectroscopy, UV/vis/IR transmission spectroscopy and X‐ray diffraction have been employed for this investigation. Deuterated substituted single crystals of KDP and DKDP also have been grown for the investigation of growth rates and Raman active mode identification purposes. The molecular vibration modes of the grown crystals, including internal modes of PO4 tetrahedrons molecular vibrations, external modes of optical phonons and hydrogen bonding modes have been determined exactly by micro‐Raman back‐scattering spectroscopy. The best pH values of the solution for the KDP crystal growth with reasonably higher growth rates from aqueous solutions that have been supersaturated ata temperature range of 30–50 °C have been found to be in the pH range of 3.2–5.4. Copyright © 2007 John Wiley & Sons, Ltd.

Defects of large-size KDP single crystals and their influence on degradation of the optical properties

It is shown that the developed method of solvent re-circulation, which provides optimum growth conditions at a constant temperature (Tcr=80°C, Vgrowth∼(0.8–1.6)×10−6cm/s, pH=4), allows to grow KDP crystals with a cross-section up to 300×300mm and a bulk laser damage threshold of ∼60J/cm2.

Influence of La3+ ions on growth and NLO properties of KDP single crystals

Single crystals of pure and Lanthanum added KDP crystals were grown from aqueous solution. The influence of La3+ ions in KDP crystals is studied. Isolated centers are formed by La3+ ions in KDP structure along (100) plane. La3+ ions incorporated into superficial crystal growth layer and slightly affect the growth process as they generate weak lattice stresses. The creation of these weak lattice stress is confirmed by Vickers's micro hardness test. The HRXRD analysis showed reduced structural defects in the La added KDP in the (100) plane than pure KDP. The incorporation of La in the crystal was confirmed by EDAX analysis. The Kurtz's powder SHG efficiency was found to be 1.5 times that of pure KDP. The UV-Vis transmission spectra of La added KDP showed excellent transmittance from 1100 nm to 340 nm and did not show any change in lower cutoff wavelength with respect to pure KDP. Laser damage threshold value has been determined using Q-switched Nd:YAG laser operating at 1064 nm and with 65 ns pulses in single shot mode. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of the Growth Rate Formula and Bulk Laser Damage Threshold KDP Crystal Growth from Aqueous Solution by the Sankaranarayanan-Ramasamy (SR) Method

A system is reported for evaporation-controlled crystal growth of potassium dihydrogen phosphate (KDP) from aqueous solution by the Sankaranarayanan−Ramasamy (SR) method. KDP (KH2PO4) single crystals of 10-, 20-, and 40-mm diameter and 60-mm height have been grown at an average growth rate of 5 mm/day from the point seed in a glass crystallizer. The growth rate formula is derived for the SR method. The grown crystals were characterized by UV−vis, laser Raman, second harmonic generation efficiency, and laser damage threshold studies. The SR method is an efficient method to grow crystals of good optical quality.

Dielectric parameters of KDP single crystals added with urea

Potassium dihydrogen orthophosphate (KDP) having superior nonlinear optical properties has been exploited for variety of applications. We have grown KDP single crystals added with urea by the slow evaporation method from aqueous solutions. Dielectric measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 313 to 423 K by the conventional parallel plate capacitor method. The present study indicates that the dielectric parameters increase with the increase in temperature but do not vary systematically with respect to impurity concentration. Also, it indicates that 0.6 mole% urea addition to KDP leads to low permittivity value dielectrics.

EDXRF determination of impurities in potassium dihydrogenphosphate single crystals and raw materials

AbstractA fast and simple preconcentration procedure for recovering various cation impurities from potassium dihydrogenphosphate (KDP) single crystals and raw materials, followed by energy‐dispersive X‐ray fluorescence analysis (EDXRF), is described. The technique is based on the adsorption of metal 8‐hydroxyquinoline complexes from aqueous solutions of KDP on activated carbon, separation of the concentrate on a Nuclepore filter and subsequent determination by EDXRF. To fix activated carbon powder on a filter surface, an amount of 1‐hexadecanol is added to the KDP solution during the preconcentration procedure. The optimum conditions for the best recovery of the impurities were established. It was shown that a preconcentration factor of 100 can be achieved and the detection limit for a number of elements was down to 0.01 µg g−1. The relative standard deviations were 6–17% for element concentrations of 0.2 µg g−1. The method was successfully applied to the determination of Fe, Co, Cu, Ni, Zn, Mn, Ti and Bi in KDP single crystals and raw materials. Copyright © 2005 John Wiley & Sons, Ltd.

Temperature dependence of the thermo-optical properties of KDP single crystal measured by thermal relaxation and thermal lens methods

In this work, thermal lens spectrometry and the thermal relaxation method were applied to determine the thermo-optical properties of KDP single crystal as a function of temperature. The results showed the expected phase transitions of the crystal at different temperatures and also provided the behavior of the thermal lens amplitude when the crystal temperature was increased. This information is relevant since this material is widely used in many optical systems, especially in high power laser cavity.

Effective Distribution Coefficients of Cation Impurities in KDP Crystals

The effective distribution coefficients К of 19 elements are measured in the {100} and {101} sectors of KDP single crystals grown from stoichiometric solutions. The results indicate that, at low impurity concentrations in the solution, К depends on the mechanism of the incorporation of cations (which form three types of defect centers in the structure of KDP) and their ionic radius. Increasing the concentrations of several divalent cations in solution may reduce their distribution coefficients because of the competition between the cations for interstitial sites in KDP.

A double acousto-optic monochromator for the uv region with improved optical characteristics based on a KDP single crystal

A double monochromator is developed and manufactured on the basis of an acousto-optic filter made of a potassium dihydrogen phosphate (KDP) single crystal. The device has an operating range of 260–540 nm and improved optical characteristics: high aperture ratio (an angular aperture of 2° and a linear aperture of 6.5x15 mm), high polarization contrast (∼108), and low level of transmission sidelobes (∼103). The spectral resolution of the monochromator at the edges of the operating range is 0.5 and 3 nm, respectively. The control frequency band is 60–150 MHz. Experimentally, it is shown that, for sound beams with equivalent geometric parameters, the diffraction efficiency provided by the KDP-based acousto-optic filter is an order of magnitude higher than that obtained with a noncollinear acousto-optic filter fabricated on the basis of crystalline quartz.

Nonlinear optical effects in Bi 12TiO 20 nanocrystallites embedded within a photopolymer matrix

Photoinduced nonlinear optical effects in large-sized (up to 20 nm) Bi 12TiO 20 (BTO) nanocrystallites incorporated within olygoether photopolymer matrix have been studied. Photoinduced optical second harmonic generation (PISHG) was measured. Nd:YAG pulsed laser ( λ=1.06 μm) was used as a source of photoinducing light. As a fundamental light source for the SHG and two-photon absorption, Er:LiYF 4 laser ( λ=2.065 μm) was used. We have found that with increasing IR pump power density, the output doubled frequency SHG signal ( λ=1.03 μ m) increases and achieves its maximum value at the pump power density about 1.4 GW/cm 2 and nanocrystallite (NC) sizes about 15 nm. The values of second-order optical susceptibilities were almost 15% smaller compared to d eff tensor of the KDP single crystals. With decreasing temperature below 22 K, the SHG signal increases. Pump–probe measurements indicate the occurrence of the SHG maximum at pump–probe delaying time of about 29 ps. This effect is explained within a framework of photoinduced anharmonic electron–phonon interaction due to the creation of electrostricted phonons. Two-photon absorption was also investigated. Quantum chemical simulations have shown that the TiO 4 structural fragments play a crucial role in the observed NLO effects. The obtained results show that the mentioned nanocomposites can be used as a powerful tool for creation of IR-operated nonlinear optical devices.

Growth of large KDP single crystals for UV spectrum range

The influence of various technological parameters of crystallization (acidity of growth solutions, crystallization temperature, growth rate, degree of solution purification) on the optical absorption of large KDP single crystals has been studied in the UV range of the spectrum. It is shown that the method of solvent recirculation with the use of the starting material with the microimpurity content not exceeding 5 × 10−5 wt % and solution ultrafiltration under the optimum crystallization conditions (tcr = 80°C, Vcr ∼ (0.8–1.6) × 10−6 cm/s, pH 4) enables one to grow KDP single crystals with cross sections up to 300 × 300 mm2 and the transmission in the vicinity of the fundamental absorption edge λ = 200 nm) equal to 86%.

Hydrodynamic conditions for growth of large KDP crystals

Three-dimensional mass transfer is simulated. The factors determining the hydrodynamic conditions for efficient mass transfer in growth of large KDP single crystals (cross sections up to 45 × 45 cm2) from solutions in a real 300-l-crystallizer are established. The conditions for the motion of the supersaturated solution to the surface of a growing crystal in the direction opposite to that of gravitation are attained. The growth mode developed provides growth rates that are five times higher of large high-quality optical KDP crystals.

Raman Study of Lattice Vibration Modes and Growth Mechanism of KDP Single Crystals

The space group theoretical analyses and assignment of the lattice modes of the KDP crystal have been made, and the Raman spectra of their growth solution have been observed in different growth regions. The attention is focused on the analysis of the 912 cm-1 band arising from the H2PO4- anions in the interface between the KDP crystals and their growth solution. This has been assigned to the asymmetrical stretching mode of the deformation P(OH)2 . From these results, the growth units of KDP crystal has been concluded to be the dimers of H2PO4- anions. We consider that the result presented here is an important step towards the development of more complete crystal growth theories.

Observation of Kossel and Kikuchi lines in thermal neutron incoherent scattering.

In this Letter we report the observation of K lines (representing collectively, Kossel and Kikuchi lines) produced by monochromatic thermal neutrons interacting with a KDP (potassium dihydrogen phosphate) single crystal. Since K lines contain phase information, these observations establish the experimental basis for direct crystallographic phasing of atomic structures containing incoherent scatterers, such as hydrogen, via thermal neutron "inside source" holography.

Lattice variation and thermal parameters of gel grown KDP crystals added with some ammonium compounds

Pure and impurity added (with NH4Cl, NH4NO3, NH4H2PO4, and (NH4)2SO4) KDP single crystals were grown by the gel method using silica gels. X-ray diffraction data were collected for powder samples and used for the estimation of lattice variation and thermal parameters like Debye-Waller factor, mean-square amplitude of vibration, Debye temperature and Debye frequency. The thermal parameters do not vary in a particular order with respect to impurity concentration. The results obtained are reported and discussed.

Electrical conductivity measurements on gel grown KDP crystals added with urea and thiourea

Pure and impurity added (with urea and thiourea) KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 30 to 140‡ C by the conventional two-probe method. The present study shows that the conductivity in KDP crystals, for both the impurities considered, increases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.

Pb4.7Ba0.3Ge3O11 Crystals as New Acoustically Induced Nonlinear Optical Materials

Acoustically induced optical second harmonic generation (SHG) and two-photon absorption (TPA) in ferroelectric Pb 4.7 Ba 0.3 Ge 3 O 11 crystals have been found. We have found that with increasing acoustical power, the SHG for YAG:Nd laser light (λ=1.06 μm) increases and achieves its maximum value at acoustical power density about 1.75 W/cm 2 . The evaluated SHG values were 23 % less comparing with X 222 tensor of the KDP single crystals. With decreasing temperature, the acoustically induced SHG signal strongly increases below 29 K. The maximal acoustically induced SHG has been observed at acoustical frequencies lying within the ranges 12-17 kHz, 22-23 kHz and above 26 kHz. This behavior reflects nonlinear superposition of the nonlinear optical susceptibilities stimulated by externally-induced electron-phonon anharmonicity. We have observed substantial increase of the TPA (for the acoustical power W= 1.8 W/cm 2 ) at high hydrostatic pressures (about 16 GPa) and low temperatures (below 16 K). This one confirms complicated influence of the electron-phonon interactions in the ferroelectrics on the observed nonlinear optical dependences.

An Investigation on the Lattice Distortion in Urea and KCl Doped KDP Single Crystals by X-ray Diffraction Studies

Potassium dihydrogen phosphate (KDP) doped with different mole concentrations of urea and KCl were grown using low temperature solution growth technique. X-ray diffraction studies were carried out on the grown crystals using a Shimadzu X-ray diffractometer with CuK α radiation. X-ray study revealed that the structures of the doped crystals are slightly distorted compared to the pure KDP crystal. This may be attributed to strains on the lattice by the adsorption of urea and KCl.

Light-induced ESR of dye-doped KDP

We measured ESR of dye-doped KDP single crystals. The dyes are Chicago Sky Blue and Amaranth. The dye molecules are exclusively included in the pyramidal part of the crystal. No signals are detected when the tinted crystals are kept in the dark. However, the crystal doped with Chicago Sky Blue shows a resonance line g = 2.00 when shed with light, the signal decays with time if the light is turned off. We have analyzed the decay of the signal with a sum of three exponetially decaying function, the longest one being almost constant in our time scale. The amplitude which has the longest time constant increases with decreasing temperature and shows an anomaly around the transition temperature.

]Electrical conductivity measurements on gel grown KDP crystals added with some ammonium compounds

Pure and impurity added [with NH4CI, NH4NO3, NH44H2PO4, (NH4)2CO3 and (NH4)2SO4] KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 28 to 140°C by the conventional two-probe method. The present study shows that the conductivity in KDP crystals, for all the five dopants considered, increases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.