Potassium Dihydrogen Phosphate Crystals Research Articles

Crystallization of KDP in the presence of 4-nitro benzoic acid, L-ornithine hydrochloride and terephthalic acid

The present study is to investigate the optical, thermal and SHG properties of grown potassium dihydrogen phosphate (KDP) crystals using slow evaporation method in the presence of 4-nitro benzoic acid, l-Ornithine Hydrochloride and Terephthalic acid. Powder crystal XRD studies confirm their structure as that of KDP. The presence of functional groups has been tested and confirmed by FTIR. UV–visible spectral analysis - Differential Reflectance Studies (DRS) is used to examine the optical properties of pure and doped KDP crystals within the wavelength range of 200–800 nm and also evaluate the band gap, refractive index, extinction coefficient and optical conductivity of the grown crystals. Thermal properties of grown crystal are analysed by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Second harmonic generation test is carried out for the grown crystals to analyse nonlinear optical (NLO) properties.

Optimal operating conditions for the rapid growth of KH2PO4 crystal by numerical simulation

Numerical simulations of the turbulent hydrodynamics and concentration in the rapid growth of potassium dihydrogen phosphate (KH2PO4 or KDP) crystals have been performed. In this work, a quadratic power-law growth model is applied, concerning the mass transfer occurring at the crystal surface during the growth process under low supersaturations. The mass transfer boundary condition is discretized by using the Over-Relaxed approach. The effects of the growth temperature and rotation rate on surface supersaturation distribution and the diffusion layer are investigated, which are critically involved in the processes of surface morphological instability and inclusion formation. Due to the kinetic limitation, the response of different types of crystal surfaces to temperature varies, with a pyramidal surface about twice as high as a prismatic face. In addition, the contour map of the growth rate combined with the coefficient of variation (C.V) for various temperatures and rotation rates is used. Uniformity of surface supersaturation is provided by lowering the growth temperature and increasing the rotation rate. Furthermore, the criteria of crystal growth strategies are proposed to optimize the process parameters and obtain favorable conditions for crystal growth, thereby facilitating defect-free and high-quality crystal formation at an appropriate growth rate.

Investigation of elastoplastic deformation in potassium dihydrogen phosphate crystals through nanoindentation and ultra-precision fly cutting experiments

Investigation of elastoplastic deformation in potassium dihydrogen phosphate crystals through nanoindentation and ultra-precision fly cutting experiments

Growth, strain, energy gap, optical, mechanical, piezoelectric, and morphology analyses of 2-methylimidazole (2MI) single crystal for NLO device fabrication

2-methylimidazole (2MI) single crystal has been successfully grown by slow evaporation solution technique (SEST) by using water as a solvent. The synthesized 2MI crystal was purified by repetitive recrystallization. Various other characterizations were carried out for the grown 2MI single crystal, such as powder X-ray diffraction (PXRD), FTIR, UV–Visible NIR, Microhardness, Photoluminescence, SEM, Piezoelectric, and SHG. The 2MI crystal was subjected to PXRD to endorse the crystalline quality of the material. The vibrational assignments and their functional groups were identified from the FTIR analysis. The UV–Visible NIR study exposes the transparency and cut-off wavelength of the 2MI crystal. The mechanical strength was investigated by Vickers microhardness tester. The surface investigation of the 2MI crystal was analyzed by a scanning electron microscope technique to obtain the presence of defects and surface texture in the developed 2MI crystal. The photoluminescence spectrum confirmed the green light emission of the crystal. The value of the piezoelectric d[Formula: see text] coefficient is measured using piezoelectric analysis. Kurtz powder’s second harmonic generation test reveals that the frequency conversion efficiency of 2MI is 3.7 times higher than that of potassium dihydrogen phosphate (KDP) crystal.

Effect of THz-bandwidth incoherent laser radiation on bulk damage in potassium dihydrogen phosphate crystals

The laser-damage performance characteristics of potassium dihydrogen phosphate (KDP) samples under exposure to a distinctive broadband incoherent laser pulse are investigated. A laser system providing such pulses is intended to explore improved energy-coupling efficiency on the target in direct-drive inertial confinement fusion experiments and provides incoherent bandwidths as large as 10 THz in a nanosecond pulse. A consequence of this bandwidth is very rapid fluctuations in intensity capable of reaching maxima much larger than the average intensity within the pulse. A custom damage-test station has been built to perform measurements with broadband incoherent pulses in order to determine what effect these fast and high-intensity oscillations have on laser damage. A set of experiments under different bandwidth and beam configurations shows the effect to be minimal when probing bulk damage in KDP. Modeling indicates this behavior is supported by long electron-relaxation times compared to the source-field fluctuations, following excitation of individual electrons in the conduction band. The results help better understand the laser-induced–damage mechanisms in KDP, and its ability to operate in broadband temporally incoherent high-energy lasers that may be particularly suitable for future laser-fusion energy systems.

Characteristics of broadband OPCPA based on DKDP crystals with different deuterations for the SEL-100 PW laser system.

We present the performances of a broadband optical parametric chirped pulse amplification (OPCPA) using partially deuterated potassium dihydrogen phosphate (DKDP) crystals with deuteration levels of 70% and 98%. When pumped by a Nd:glass double frequency laser, the OPCPA system using the 98% deuterated DKDP crystal achieves a broad bandwidth of 189 nm (full width at 1/e2 maximum) from 836 nm to 1025 nm. For the DKDP crystal with length of 43 mm, the pump-to-signal conversion efficiency reaches 28.4% and the compressed pulse duration is 13.7 fs. For a 70% deuterated DKDP crystal with a length of 30 mm, the amplified spectrum ranges from 846-1021 nm, the compressed pulse duration is 15.7 fs, and the conversion efficiency is 25.5%. These results demonstrate the potential of DKDP crystals with higher deuteration as promising nonlinear crystals for use as final amplifiers in 100 Petawatt (PW) laser systems, supporting compression pulse duration shorter than 15 fs.

Quantitative identification of deposited energy in UV-transmitted KDP crystals from perspectives of electronic defects, atomic structure and sub-bandgap disturbance

The laser-induced damage threshold (LIDT) of ultra-precision machined potassium dihydrogen phosphate (KDP) crystal is always lower than the intrinsic threshold.

Effect of Organic Entities on the Performance of Potassium Dihydrogen Phosphate (KDP) Crystals

The 0.5mol l-cystine and 2mol oxalic acid doped in potassium dihydrogen phosphate crystals have been developed by slow evaporation method at room temperature. The structural properties of the grown crystal were analyzed by powder X-ray diffraction technique. The functional groups of grown crystals were successfully identified using FTIR spectral analysis. The optical transparency of the grown crystals is examined in the range of 200-900 nm using UV-visible studies. The optical transmittance is found to be 87 % of the grown crystal. The energy band gap (Eg) of the grown crystal was calculated at 3 eV. The Kurtz- Perry test has been employed to determine the SHG efficiency and the SHG efficiency of the grown crystal was 0.5 % of pure KDP crystal tested by Kurtz-Perry powder technique.

Study of the surface damage threshold and mechanism of KDP crystal under ultrashort laser irradiation

Here, we investigate the mechanism of surface damage threshold anisotropy induced by ultrashort laser in potassium dihydrogen phosphate (KDP) crystal. Carrier-lattice nonequilibrium interaction is simulated based on Brillouin light-scattering (BLS) spectroscopy and a complete self-consistent model to obtain the time evolution of carrier density and temperature as well as lattice temperature. The results indicate that the trend of the lattice temperature is consistent with the experimental phenomena. Meanwhile, the electron-phonon coupling effect, in addition to the electron density traditionally considered, is an important factor affecting damage and is a major contributor to the anisotropy of the damage threshold.

First-principles study on the electronic structures and optical properties of Mg-doped KDP crystal

First-principles method was employed to study the defect formation energy, electronic structure, and optical properties of Potassium Dihydrogen Phosphate (KDP) crystals doped with Mg in both paraelectric phase (PE-KDP) and ferroelectric phase (FE-KDP). Additionally, we employed the HSE hybrid density functional to address the issue of “band gap” and utilized the finite size correction-finite volume (FNV) method to rectify defect formation energies. Due to hybridization of Mg-3s orbitals with O-2p orbitals, a defect energy level is created at the conduction band minimum (CBM), resulting in the band gap of Mg-doped KDP crystals being smaller than that of perfect crystals. Moreover, the incorporation of Mg leads to significant lattice distortions and alters bond lengths, particularly the O–Mg bonds, which are stretched by 0.65–0.77 Å. The optical spectra also have been obtained under the consideration of electron-phonon coupling. The absorption peak locates at 4.37 eV (284 nm) in PE-KDP. The absorption peak locates at 4.66 eV (266 nm) in FE-KDP. Moreover, the significant Stokes shifts (3.67 eV and 2.9 eV) observed in Mg-doped KDP crystals were attributed to lattice relaxation energy and distortions induced by the substitution. The calculated results indicate that the quality of the KDP crystals may be reduce by introducing Mg-impurities. The work provides valuable insights into the optical characteristics of Mg-doped KDP crystals and their potential applications in laser technology.

Concentration characterization of underlying intrinsic defects accompany with surface structural defects and their effect on laser damage resistance

During ultra-precision processing of potassium dihydrogen phosphate (KDP) crystals, various macro-structural surface defects are inevitably introduced, but there is no monotonic relationship between different macro-defects and laser-induced damage threshold (LIDT). Therefore, a single macro-perspective cannot fundamentally reveal the causation for low LIDT. In this work, energy, photoelectron spectra characterization and photoluminescence characteristics of surface were adopted to determine the type and concentration of intrinsic defects accompany with macro-structural defects. First-principles calculation was applied to explore the influence of oxygen vacancy (VO) defect concentration on performance in terms of crystal structure, electronic structure, and optical properties. The results show that the causation for low LIDT of cracks is VO defects. With the increase of VO defect concentration, PO43- group would collapse, leading to a decrease in the stability of crystal structure. High concentration of VO defects would introduce defective-energy level, causing irreversible alteration in energy level. Free electrons are susceptible to absorb photons and transition due to defective-energy level, severely reducing the laser damage resistance of components. This work reveals the influence of surface defects on laser damage from intrinsic defects at atomic-level, which is significance for the suppression of surface defects during ultra-precision processing and effective improvement of laser damage resistance of KDP.

Computational study of self-trapped hole in KH2PO4–Si crystal

We use the DFT + U approach to investigate the properties of self-trapped holes (STHs) in silicon (Si)-doped potassium dihydrogen phosphate (KH2PO4) crystal. The calculated electronic structure and spin density indicate that the hole is trapped by an oxygen around the Si atom. The STH is stable under room temperature, as the self-trapped energy is as high as 0.50 eV. The optical properties of the localized and delocalized holes of KH2PO4-Si crystals are also calculated, and the results show that the emission energy of the STH [3.62 eV (343 nm)] is consistent with the experimental photoluminescence of KH2PO4 (342 nm), and the absorption peaks of the STH [3.58 eV (346 nm) and 5.56 eV (223 nm)] are located in the ultraviolet (UV) region, which indicates a close connection between the STH and the absorption band in the UV region. The absorption peak of the delocalized hole [3.44 eV (360 nm)] is consistent with the experimental absorption band (360 nm). Therefore, Si impurities result in UV absorption and a sharp decline of damage threshold in KH2PO4.

The femtosecond structure of extreme contrast, multi-terawatt second-harmonic laser pulses at 400 nm

Ultrahigh intensity contrast and short pulse laser–solid interactions offer an attractive platform for investigating high-energy-density matter, particularly in the context of structured and ultra-thin targets that form hot, dense plasma conditions. Harmonic generation can improve the contrast of laser pulses by several orders of magnitude. In this study, we present the characterization of extreme contrast, relativistic intensity second-harmonic pulses at 400 nm, using the self-diffraction frequency-resolved optical gating technique. The 400 nm pulses were generated at various input intensities using potassium dihydrogen phosphate and lithium triborate crystals. Our observations reveal the presence of spectral broadening, pulse compression, and complex structures at higher input intensities. We see that extreme contrast, few tens of femtosecond pulses can have multiple “prepulses” at the 100s femtosecond scale as large as ten percent of the peak value. These can preionize a solid significantly and may influence the interaction. Simulations based on nonlinear pulse propagation equations reinforce our findings.

Nucleation and Growth Kinetics of Potassium Dihydrogen Phosphate Crystal in Stirred Tank Crystallizer

Nucleation and Growth Kinetics of Potassium Dihydrogen Phosphate Crystal in Stirred Tank Crystallizer

Calculating the area of a particular deformation region of an optical surface based on the finite element method

To study the deformation of an optical surface and its effect on optical performance, a method based on the finite element method for calculating the area of a particular deformation region of an optical surface is proposed, and a concept of effective area ratio is further introduced to describe the effect of deformation on optical performance. The principle of the method is presented, and the deformation of a potassium dihydrogen phosphate (KH2PO4, KDP) crystal is studied using this method, while the calculation accuracy is discussed. The results demonstrate that the method and the concept of effective area ratio are available for studying the deformation of an optical surface and its effect on optical performance.

First-principles calculation of KH2PO4 anharmonic force constants phonon dispersion curves

The laser-induced damage threshold of potassium dihydrogen phosphate (KDP) crystal is far lower than the theoretical value. The damage mechanism of KDP crystal cannot be clearly determined by various experiments and first-principles density functional theory (DFT) calculation of electronic properties. We attempt to explore the impact of phonons on the damage process by studying lattice dynamics. The phonon dispersion curves of intrinsic KDP crystal with harmonic approximation and anharmonic effect are studied by using the first-principles DFT calculations. With harmonic approximation, there are three large imaginary frequencies in the PE phase, which are the O–H stretching soft modes leading to the FE-PE phase transition. For the large displacement vibration of H atoms in PE phase, the room-temperature phonon dispersion curves with anharmonic effect are calculated. The imaginary frequency caused by three O–H stretching soft modes disappears. Our results have important reference significance for understanding the damage mechanism of KDP crystal.

Electronic structures and optical properties of defective KDP with V-doped: A first-principles study

The effect of V single-doping on the defect formation energies, electronic structures, and optical properties of potassium dihydrogen phosphate (KH2PO4, KDP) crystals in tetragonal and orthorhombic phases has been investigated using first-principles calculations based on density functional theory (DFT). Meanwhile, we apply the HSE06 hybrid functional to correct the "band-edge" problem as well as the FNV correction method for the finite-size system to revise the defect formation energy. Our research reveals that V doping could lead to a marked expansion of the lattice at the defect sites, making the crystal susceptible to damage. The band gap of the V-KDP crystals is smaller than that of the perfect KDP crystals because the V-3d orbitals hybridize with the O-2p orbitals to create defective energy levels at the conduction band minimum (CBM). Furthermore, we used configuration coordinate diagrams (CCD) and optical spectra to analyze the optical properties of V defects and found absorption peaks at 6.01 eV (206 nm) in tetragonal KDP and 5.68 eV (218 nm) in orthorhombic KDP. The calculation results indicate that the quality of the KDP crystals can be enhanced by reducing the concentration of V-impurities, which can serve as a theoretical guide for the practical application of KDP.

Final amplifier of an ultra-intense all-OPCPA system with 13-J output signal energy and 41% pump-to-signal conversion efficiency.

Optical parametric chirped-pulse amplification (OPCPA) using high-energy Nd:glass lasers has the potential to produce ultra-intense pulses (>1023 W/cm2). We report on the performance of the final high-efficiency amplifier in an OPCPA system based on large-aperture (63 × 63-mm2) partially deuterated potassium dihydrogen phosphate (DKDP) crystals. The seed beam (180-nm bandwidth, 110 mJ) was provided by the preceding OPCPA stages. A maximum pump-to-signal conversion efficiency of 41% and signal energy up to 13 J were achieved with a 52-mm-long DKDP crystal due to the flattop super-Gaussian pump beam profile and flat-in-time pulse shape.

Impact of longitudinal phase-matching variations on three-wave nonlinear interactions

A general study of three-wave nonlinear mixing in the presence of longitudinal variations in phase-matching conditions is presented. The efficiency of second-harmonic generation and optical parametric amplification is quantified using a normalized set of equations and a polynomial description of the wave-vector mismatch as a function of the longitudinal coordinate. These modeling results are used to estimate the impact of spatial variations in wave-vector mismatch experimentally obtained for five partially deuterated potassium dihydrogen phosphate crystals. The longitudinal inhomogeneities in the properties of crystals of similar quality are not expected to have a significant impact on their use for second-harmonic generation and optical parametric amplification, but the efficiency of nonlinear processes in crystals with larger variations could decrease.

Examining the change of half-period voltage in longitudinal electro-optic modulation and residual stress of potassium dihydrogen phosphate crystal.

In this paper, the voltage-transmittance curvesKDP crystals were measured accurately between two crossed or parallel polarizers using longitudinal electro-optic effect. The end faces of rectangular KDP samples were coated with ring-shaped electrodes using conductive silver paint (CSP). The change of half period voltage U i has been investigated. A method for quantitative characterization of residual stress has been proposed, based on deviation voltage U d. The results demonstrate that loading voltage is close to the integration of electric field intensity in crystal along the optical path when the CSP ring electrodes have a large outer radius R, small inner radius r, and long-distance d. The half-period voltage U i is also close to longitudinal half-wave voltage U π in these circumstances. The unclamped electro-optic coefficient γ63σ of KDP crystal at room temperature was measured as 10.24±0.05p m/V at the wavelength of 632.8nm.