Characterization of biaxial crystals for tangentially phase-matched frequency conversion

Ultraviolet radiation has been generated by tangentially phase-matched sum-frequency mixing in biaxial L-arginine phosphate (LAP) crystal for the first time using Nd:YAG output at 1064 nm and Rh 6G dye laser output at 560 nm as the two input sources. Characterization has also been made of such a cheap, biaxial crystal for its possible use in devices for tangentially phase-matched short wavelength generation. If the crystal is of proper cut, thickness and quality so that its maximum capability can be exploited it can replace the potassium dihydrogen phosphate (KDP) group of crystals for various applications.     

Photorefraction in the ultraviolet: Materials and effects

Doped as well as nominally pure crystals of Lithium Niobate (LiNbO₃), -Arginine Phosphate (LAP), Lithium Iodate (LiIO₃), Potassium Dihydrogen Phosphate (KDP), Lithium Formate (LFM), Beta-Barium Borate (BBO), and lithium tetra borate were grown and investigated for photorefractive effects at ultraviolet wavelengths down to 333 nm. In nominally undoped LiNbO₃ crystals strong beam coupling effects were observed. In contrast to the visible we revealed a diffusion-dominated charge transport mechanism based on holes, and a low photovoltaic field in the order of 550 V/cm. With such a crystal we investigated the modulation transfer function of a lensless image projection system based on a phase conjugation scheme. A spatial frequency response beyond 2800 line pairs per millimeter was observed. Photorefractive beam coupling was also obtained in LiIO₃. Light-induced scattering was detected in iron-doped LiIO₃ whereas as-grown LAP material did not exhibit any observable photorefractive effects. However, 100 kV X-ray irradiation seems to induce material defects which can lead to weak light-induced scattering at 351 nm. In all other above-mentioned materials, doped as well as undoped, light-induced scattering could not be observed. On the other hand, this is appreciated in all the applications where the crystals are used as nonlinear material for optical frequency conversion.     

KDP晶体三倍频实验和分析

报道了ＫＤＰ晶体中的三倍频产生的实验研究，计算了比较了直接三倍频过程和级联过程对ＫＤＰ晶体三阶有效非线性系数的贡献，并探讨了ＫＤＰ作为非线性晶体材料三阶非线性系数测量基准的可行性。     

退火温度对KDP晶体光学均匀性的影响研究

 研究了磷酸二氢钾（KDP）晶体热退火前后光学均匀性的变化，发现适当温度下退火可以降低KDP晶体的内应力，提高晶体的消光比，从而提高晶体的光学均匀性。实验证明，50℃下退火即可消除部分内应力，110℃下退火可以消除生长鬼影和鬼线。但是,退火温度太高（如170℃）,也可能使晶体的均匀性降低。     

Effect of magnetic treatment of KDP and ADP crystals and solutions on their equilibrium temperature

The effect of magnetic treatment of KDP and ADP crystals and solutions on their equilibrium temperature has been revealed and studied. The change in the temperature reaches a maximum immediately after the magnetization. Then, the effect decreases monotonically, and the equilibrium temperature approaches the equilibrium value for 5 h. It has been found that the observed decrease in the solubility depends on the impurity concentration, and it is maximum in magnetically treated KDP crystals with a chromium impurity; then, it decreases in the series: KDP crystal, KDP-ADP crystals in KDP-ADP solution, KDP crystal in KDP-ADP solution, and KDP solution. For all five systems under study, the relaxation times have been determined. It has been revealed that the effect rapidly increases and reaches saturation at B = 0.02 T. The energy effects in the crystals and solutions have been estimated.     

KDP晶体全口径最佳入射角优化方法

根据正交偏振干涉测量法(OPI)获得的KDP晶体折射率的空间分布数据求解KDP晶体内部失谐角分布,进而建立了倍频及和频KDP晶体全口径最佳入射角的优化模型和方法。分析讨论了不同折射率畸变程度和不同功率密度入射情况下倍频及和频晶体入射角的变化规律。在此基础上,对KDP晶体的全口径最佳入射角进行了优化。结果表明:当KDP晶体折射率畸变程度较大时,倍频晶体对折射率变化较为敏感,而和频晶体对折射率变化则相对不敏感。在实际工作中,首先在假设倍频晶体折射率分布均匀的前提下,对和频晶体的最佳入射角进行优化,而后通过适当调整倍频晶体及和频晶体的入射角,最终确定倍频晶体及和频晶体的全口径最佳入射角。     

KDP晶体中位错的研究

本文用化学腐蚀方法揭示了KDP晶体中(001)和(100)晶面上的位错蚀坑,观察测量了不同质量的晶体中位错的形态、类型、分布和密度,并简要讨论了位错的成因。 关键词：     

季氨盐对KDP晶体的光学特性影响

 生长了不同季氨盐掺杂浓度的KDP晶体，其锥光干涉实验显示了晶体的内应力引起的双折射和双轴晶特性较明显。透过率特性的实验结果表明，不同浓度的季氨盐对KDP晶体的光学均匀性有较大影响。报道了掺季氨盐0.001%的KDP晶体的异常光学透过率特性以及晶体具有三维变化的波片效应和旋光特性。     

硫酸盐对KDP晶体质量的影响

 利用“点籽晶”快速生长技术生长了掺杂硫酸钾（K₂SO₄）的磷酸二氢钾（KDP）晶体，并对硫酸根类杂质离子对晶体的结构及光学质量的影响进行了研究。结果表明：在掺杂相对含量为50×10^-6条件下，K₂SO₄开始对KDP晶体产生一定影响，主要表现在不同扇形区域的结构略有改变，其原因主要在于硫酸根与KDP晶体各扇形结构有关；杂质粒子对晶体透过率、单轴性没有明显影响，但是热膨胀系数增大，光损伤阈值略有降低。     

Effect of a preliminary magnetic treatment of KDP crystals and solutions on the equilibrium between them

Measurements of the temperature of equilibrium between a nonmagnetic KDP crystal and its aqueous solution demonstrated that the magnetization of the KDP crystal or its solution causes a change in this temperature. It was shown that the effect of magnetization has the maximum magnitude immediately after magnetization and then weakens monotonically, virtually disappearing within 5 h. The effect exhibits saturation at magnetic induction values within B = 0.02−2.0 T. The most pronounced decrease in the solubility was observed for magnetized KDP crystals doped with chromium; the decrease for magnetized KDP crystals without chromium was more moderate and yet smaller for magnetized KDP solutions. The lifetimes of the magneto-induced state for these three cases were 2.5, 2.8, and 2.6 h, respectively.     

Characterization studies on the additives mixed l-arginine phosphate monohydrate (LAP) crystals

l-arginine phosphate monohydrate (LAP), potassium thiocyanate (KSCN) mixed LAP (LAP:KSCN) and sodium sulfite (Na₂SO₃) mixed LAP (LAP:Na₂SO₃) single crystals were grown by slow cooling technique. The effect of microbial contamination and coloration on the growth solutions was studied. The crystalline powders of the grown crystals were examined by X-ray diffraction and the lattice parameters of the crystals were estimated. From the FTIR spectroscopic analysis, various functional group frequencies associated with the crystals were assigned. Vickers microhardness studies were done on {1 0 0} faces for pure and additives mixed LAP crystals. From the preliminary surface second harmonic generation (SHG) results, it was found that the SHG intensity at (1 0 0) face of LAP:KSCN crystal was much stronger than that of pure LAP.     

夹持方式和加工误差对大口径薄型KDP晶体附加面形的影响

惯性约束聚变频率转换系统中,大口径薄型KDP晶体的面形质量是影响频率转换效率能否达到设计要求的关键因素之一。针对45放置状态下口径为400 mm400 mm的三倍频KDP晶体,采用ANSYS有限元分析软件,建立了不同夹持方式和具有不同加工误差的KDP晶体模型和夹具模型,分析了加工误差对不同夹持方式下KDP晶体附加面形的影响,给出了不同加工误差和不同夹持情况下,KDP晶体附加面形的P-V值和RMS值。研究结果表明,夹持方式和加工误差是引起KDP晶体附加面形变化的重要因素,正面压条夹持方式即使在晶体和夹具存在加工误差时也可以较好地控制晶体的附加面形。     

Linear and nonlinear optical properties of dye-doped KDP crystals: Effect of thermal treatment

Potassium dihydrogen phosphate crystals (KDP, KH₂PO₄) doped with the organic xylenol orange (XO) dye are grown, the XO concentration in the crystal matrix is about 10 ppm. The spectral and luminescent properties of nominally pure, dye-doped and dye-doped/annealed at 150 °C crystals (KDP, KDP:XO and KDP:XO_an) were measured. The annealing temperature effect on the degree of dye protonation in the crystal matrix is established. Analysis of the IR-absorption spectra reveals a strong interaction between the incorporated dye molecules and the hydrogen subsystem of the matrix. The nonlinear optical (NLO) properties of KDP, KDP:XO and KDP:XO_an crystals are studied within the self-action effect of picosecond laser pulses at 532 nm. The mechanism of photoinduced bleaching and the effects of laser beam self-focusing (in KDP) and self-defocusing (in KDP:XO and KDP:XO_an) are supposed to be due to resonance excitation of the subsystems of intrinsic defects and dye molecules, correspondingly. For KDP:XO_an it is shown that thermal annealing of intrinsic crystal defects leads to domination of more effective NLO response of the subsystem of dye molecules that is correlated with photoluminescence data.     

Studies on growth,structural, optical and mechanical properties of xylenol orange dye admixtured l-arginine phosphate single crystal

Bulk single crystals of pure and xylenol orange (XO) admixtured l-arginine phosphate (LAP) were grown by slow cooling technique. The cell parameters and crystallinity of pure and dye admixtured LAP crystals were confirmed by single crystal and powder X-ray diffraction analyses. HRXRD analysis reveals the presence of xylenol orange dye in interstitial site of LAP crystal lattice and it confirms the crystalline perfection of grown crystals. The functional groups of grown crystals were confirmed by FTIR spectral analysis. UV–vis transmission studies show the characteristic absorption of xylenol orange admixtured LAP crystal. Vickers’ microhardness and laser damage threshold studies were carried out on these crystals. Kurtz and Perry powder test was conducted to measure the second harmonic generation efficiency of pure and dye admixtured LAP crystals.     

Raman gains of ADP and KDP crystals

In this paper, the Raman gain coefficients of ammonium dihydrogen phosphate(ADP) and potassium dihydrogen phosphate(KDP) crystals are measured. By using a pump source of a 30-ps, 532-nm laser, the gain coefficients of ADP and KDP are 1.22 cm/GW, and 0.91 cm/GW, respectively. While for a 20-ps, 355-nm pump laser, the gain coefficients of these two crystals are similar, which are 1.95 cm/GW for ADP and 1.86 for KDP. The present results indicate that for ultra-violet frequency conversion, the problem of stimulated Raman scattering for ADP crystal will not be more serious than that for KDP crystal. Considering other advantages such the larger nonlinear optical coefficient, higher laser damage threshold,and lower noncritical phase-matching temperature, it can be anticipated that ADP will be a powerful competitor to KDP in large aperture, high energy third-harmonic generation or fourth-harmonic generation applications.     

含磷酸胍基间作用的磷酸双乙酸胍晶体电子结构与光学性质研究

基于磷酸胍基间作用在L-精氨酸磷酸盐晶体特异性与生物化学功能中的重要角色,已制备了含有磷酸胍基的新晶体磷酸双乙酸胍.本文采用第一性原理计算了磷酸双乙酸胍晶体的电子结构与三个晶向上的光学性质,探讨了其中基团间作用与光学性质的关联.结果表明,磷酸双乙酸胍晶体能隙为4.77 eV,远小于磷酸二氢钾晶体,更易吸收光子,在胍基、羧基与磷酸根上发生电子跃迁.磷酸双乙酸胍晶体在[100]和[010]方向光学性质相近,[001]晶向上胍基N-2p在价带内电子跃迁产生强吸收,能量损失高且分布较窄,光学应用受到限制,该研究对理解和研究磷酸双乙酸胍晶体中基团间作用及其光学性质奠定了良好的基础.     

热退火对KDP晶体损伤阈值的影响（英）

研究了不同退火温度下磷酸二氢钾（KDP）晶体的透过光谱和损伤阈值的变化。发现热退火对晶体的透过光谱没有影响,退火温度分别为140 ℃和160 ℃时晶体的损伤阈值没有明显变化。但是在150 ℃下,晶体的损伤阈值提高了约1.4倍。实验证明150 ℃下的热退火对提高晶体的损伤阈值效果最好。     

Analysis on suitability of pure and α-Histidine doped KDP crystals in high speed applications

Ferroelectric Potassium Dihydrogen Phosphate (KDP) crystals are widely used in modern short wavelength laser techniques, non-linear and integrated optics. The pure and α-Histidine doped KDP crystals were procured from SRM Institute of Science and Technology, Chennai. The presence of additive in the doped KDP crystal is confirmed through X-Ray diffraction patterns and the lattice parameters were evaluated. Also, Fourier Transform Infrared spectrum confirms the presence of α-Histidine in the doped crystals. The dielectric behaviour of the pure and doped crystals have been studied in the microwave region using K-band microwave bench equipped with the Gunn oscillator and guided with rectangular wave guide.     

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

We 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.     

杂质对KDP晶体光学质量的影响

 研究了几类可能出现在KDP晶体的生长溶液中的有机物杂质和无机阴离子杂质基团对KDP晶体散射、透过率、光损伤阈值等光学质量的影响，结果表明，不同种类的杂质的影响并不相同，造成这一结果的根本原因在于杂质离子的结构及其与晶体表面原子成键能力的不同。