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A series of KDP crystals at different rotation speeds ranging from 9 to 120 rpm were grown by rapid growth method. The results fully demonstrate that rotation speed as a key kinetic parameter has a great influence on the whole crystallization process. Moreover, an important characteristic has been proved that the growth rates along X and Z-direction increase with the increase of rotation speed lower than 100 rpm, while the rates of X-direction are always greater than Z-direction. Combined with numerical simulation method, the correlations of solution stability with kinetic factors including rotation speed, crystal size and growth platform are explored in detail. During the crystallization process, the thickness of boundary layer decrease and a higher flow rate is caused with the increase of rotation speed below 100 rpm, and the generation of inclusions at lower speed may be associated with the slower flow rate of growth solution. The stability of solution gradually decreases as the rotation speed ranges from 100 to 120 rpm. Furthermore, the computed results of Re imply that reducing rotation speed as increasing of crystal size may be an effective method to obtain high-quality and large-scale KDP crystal by rapid growth technique. Comparing to the growing platform with four columns, the platform with two circular connecting columns play an active role in influencing the growth rate of KDP crystal, especially in axial direction.

For KDP and 70%-DKDP crystals, knowledge of thermal-stress distribution induced by weak absorption effect is crucial for their applications, especially in high-power laser systems. Based on photo-thermal common-path interferometry (PCI) technique, the correlations of weak absorption effect with different crystal orientations were systematically evaluated at 1064 nm. An obviously anisotropic property is demonstrated, and a similar pattern of z > x > I > II is also represented for KDP and 70%-DKDP crystals. More importantly, crystal uniformity could be reflected by the weak absorption results, indicating that PCI method could be considered as a novel way to identify the crystal quality. Meanwhile, Thermal parameters including thermal expansion and thermal conductivity were obtained. Using the finite-element method (FEM), the temperature gradients and thermal-stresses along z and x-cut samples were distinctly explored, implying that the corresponding distributions are mainly attributed to crystal orientations. Importantly, another fundamental factor is confirmed that the variation of deuterium content could influence the behaviors of temperature gradients and thermal-stresses distributions. Thus, taking advantage of PCI and FEM as a new approach is more conducive to better understanding the mechanism of laser-matter interactions.

The cracking of KDP crystals during the growth & fabrication process is a serious problem that limits their application in the large-aperture high-power laser system; furthermore, the cracking is mainly attributed to their high brittleness. In order to explore the mechanical parameters related to KDP crystal cracking in detail, we measured the fracture toughness of KDP crystals as a function of temperature using the single-edge notched beam (SENB) method up to 170 °C. Meanwhile, the effects of crystallographic orientation, annealing and loading rate on the fracture toughness values were investigated in detail. Strong orientation dependence was observed on the fracture toughness of KDP crystals, and the relationship was concluded as follows: x-cut > type II > type I > z-cut. With the increase in temperature, the fracture toughness of crystals increased and reached its maximum value at 160 °C; then, it decreased, indicating that 160 °C is the temperature at which brittle-to-ductile transition occurs. Using an optical microscope, it was observed that the fractured surfaces of the samples become gradually rough with the increase in temperature. This may offer a viewpoint for understanding the dependence of fracture toughness on temperature. Furthermore, annealing and decrease in the loading rate were conducive to the significant increase in the fracture toughness of KDP crystals.

Large sized Fresnoite Ba 2 TiSi 2 O 8 single crystals were grown by the Czochralski method. Using coordinate transformation methods, the relative dielectric, piezoelectric and elastic constants of Fresnoite Ba 2 TiSi 2 O 8 as a function of orientation were investigated, and their two- and three-dimensional spatial distributions are presented. From them, the maximum values of the piezoelectric coefficients and the corresponding rotation angle can be obtained. The maximum values of coefficients d 22 ∗ , d 23 ∗ , d 24 , ∗ d 32 ∗ , d 33 ∗ and d 34 ∗ were achieved for rotation angles of 40°, 32°, 0°, 58°, 50° and 90°, respectively, and are on the order of 8.7, −4.7, 17.5, 4.7, 8.7 and 17.5 pC/N, respectively. Furthermore, the validity of the electromechanical properties investigation as a function of orientation was verified. The relative dielectric permittivity, elastic constant and piezoelectric coefficient of a ZXl50 o cut rod were calculated and found to be 14.1, 8.7 pC/N and 11.2 pm 2 /N, respectively, in good agreement with the experimental values of 12.7, 9.1 pC/N and 11.7 pm 2 /N. This investigation is important in providing direction for theoretical research and device design of piezoelectric Ba 2 TiSi 2 O 8 crystals.

The phenomenon of the cracking of KDP z-cut seed crystals with a series of sizes due to the temperature difference of the growth solution was explored in detail. Thermal stress generated in the KDP seed crystal at the moment of cracking was calculated using the finite-element method. Temperature differences leading to cracking for heated samples were nearly twice those of cooled specimens. For the cooled samples, the cracks occurred mainly along the (100), (110) and (001) crystal planes and expanded from the sample periphery to the interior spaces, and the opposite crack propagation direction was displayed in the heated samples, with cracks observed mainly along the (110) plane. More importantly, the temperature differences were observed to decrease with an increase in the sample size. In addition, the calculated results indicated that the field distribution of tensile stress is coincident with the points of crack initiation. The maximum stresses calculated were found to be greater than the fracture strength of 6.67 MPa for the KDP crystal along the [100] direction, and the direction of large stresses was found to be normal to the fracture surface. It is interesting that the maximum stress in fracture crystals decreases with an increase in the crystal size as cracks are generated.

A large sized Nd-doped Ca2Ga2SiO7 single crystal was successfully grown by the Czochralski technique. The effective segregation coefficient of Nd3+ was measured to be 1.16. The thermal, spectroscopic and laser properties were systematically investigated. The thermal conductivity was found to increase with increasing temperature, exhibiting glass or alloy like behavior, and is inherently associated with the disordered structure of the Ca2Ga2SiO7 crystal. The polarized absorption and fluorescence spectra were measured at room temperature, and the spectrum parameters were calculated using the Judd-Ofelt theory. Furthermore, continuous wave laser operation at 1.06 μm along the crystallographic a- and c-axes was demonstrated. A laser output power of 430 mW with an optical conversion efficiency of 14.2% and a slope efficiency of 16.7% was achieved. These results show that Nd:Ca2Ga2SiO7 holds excellent promise for use as a disordered crystalline laser material.

Potassium dihydrogen phosphate (KDP) crystals were grown from aqueous solutions with different concentrations of cyclohexane diamine tetraacetic acid (CDTA) by the “point seed” rapid growth technique. The effects of CDTA on the surface micro morphology of KDP crystals were systematically studied by atomic force microscopy. The prismatic face growth rates of KDP crystals grown from various solutions were measured by a laser polarization interference system. The results shown that the steps became smooth after CDTA doping. When the doping concentration of CDTA is 100 ppm, the bunching of steps on the (100) face reduced dramatically and the step velocity increased obviously due to the complexation between CDTA and the metal impurities in the original solution. When the doping concentration of CDTA is 500 ppm, the excess CDTA adsorbed on the growth surface and impeded the step movement, leading to an increase in step bunching and reduction in step velocity compared with the situation of 100 ppm.

Using the Z-scan method, the nonlinear optical absorption property of carboxyl-functionalized graphene oxide (GO) was researched for the first time. The strong optical limiting (OL) effect was found in carboxyl-GO, which can be attributed to the two-photon absorption (2PA). At 532-nm excitation condition, the threshold of OL behavior is only 8% of that at 1064 nm excitation, and the saturable intensity $I_{s}$ as well as the 2PA coefficient β2 are 1.31 GW/cm2 and 0.17 cm/GW, respectively. It indicates that carboxyl-GO is an excellent nanomaterial for OL application, especially in short wavelength scope.

A series of potassium dihydrogen phosphate (KDP) crystals and Fe3+ doped KDP crystals were grown at different temperatures and at the same supersaturation value of 0.02. The prismatic face growth rates of the KDP crystals were measured using a laser polarization interference system. The surface morphologies of the growth steps on the {100} face were comparatively studied using an atomic force microscope systematically. The results showed that the bunching of steps was related to the supersaturation interval in which it was located, and approached the supersaturation dead zone of σd in which the bunching and the slope of the steps were high. The supersaturation dead zone σd and linear zone σ* decreased with rising temperature. Varying the temperature caused considerable changes in the growth speed, step morphology and step motion speed. For the crystal grown in a doped solution, the bunching and slope of the steps reached a maximum value at around 45 °C. It was interesting that the crystal growth rate in the doped solution was higher than that in the undoped solution at around 65 °C and 75 °C, the bunching of the steps was reduced and the width of the steps widened significantly. At the same supersaturation, the growth rate increased with rising temperature and the steps became straight.

Transient numerical calculations were carried out to predict the evolution of temperature and thermal stress in traditionally grown large-size KDP crystals during the removal process, considering two methods that are used to accomplish the crystal extraction. The influence of the crystal size and the difference of temperature between the crystal and environment on the stresses inside the KDP crystals were also investigated in detail. Results indicate that, in both processes of isolating crystals, the highest stress transfers from the crystal periphery to the internal part from the early to the later time stage. In the case of extracting the crystal from solution directly after crystallization and exposing to air, the maximum stress at the crystal periphery is larger than that inside the crystal, and the probability of failure from the outside surface of crystals is large. In the case of retaining the solution for a time after crystallization, the maximum stress in the crystal internal region is larger than that of the crystal surface, leading to a large possibility to originate cracks in the inner region. Both increased crystal sizes and increased temperature differences between the crystals and the environment at the end of crystal growth are factors which aggravate crystal cracking. The maximum stress in crystals in the case of retaining the solution is less than that in the case of extracting the solution, which brings about a decreased likelihood of cracking. Thus, retaining solution for a period of time after the growth is completed, such as 96 h, is suggested to be adopted to accomplish successful crystal extraction.

Two new organic&ndash, inorganic hybrid molecular single crystals, 4-Iodoanilinium perchlorate 18-crown-6 (1) and 4-Iodoanilinium borofluorate 18-crown-6 (2), with large sizes and high thermal stability were successfully synthesized by solution method. Their structures, phase purities, thermal stability, dielectric, absorption and fluorescence spectra were systematically investigated for potential applications. Compounds 1 and 2 crystallize in orthorhombic crystal system, in same space group, namely Pnma. The thermal measurements shown 1 and 2 maintain high thermal stability up to 150 &deg, C. The temperature dependency of dielectric constant was studied, and no distinct anomaly was observed. The band gap were calculated to be 3.38 eV and 3.57 eV for 1 and 2, respectively, slightly smaller than those of layer perovskite (benzylammonium)2PbCl4 semiconducting materials, which have potential applications in optoelectronic detection field. The investigations throw light on the semiconductor properties of organic&ndash, inorganic hybrid crown type material and provide two types of crown compounds with high thermal stability.

A series of trace Fe3+-doped KH2PO4 single crystals were grown using the conventional temperature cooling method. The Fe3+ ion content in the as-grown crystals and the corresponding transmission spectrum were measured, respectively. With an increase of Fe3+ ion concentration, the transmittance of the crystal gradually decreases within the wavelength range of 200 nm to 370 nm. Under picosecond pulse laser irradiation, third-order nonlinear optical characteristics were systematically measured at λ = 532 nm. The existence of nonlinear absorption and nonlinear refraction was demonstrated. The results show that the nonlinear refractive index n2 is positive, indicating the presence of a self-focusing effect for the as-grown crystals. Specially, nonlinear absorption and refraction have a heavy dependence on the Fe3+ ion content and crystal directions (II and z). With increasing Fe3+ ion concentration, a significant variation has been observed with respect to the nonlinear absorption coefficient β, nonlinear refractive index n2 and third-order nonlinear susceptibility χ(3). A similar pattern for II < z has been presented for nonlinear absorption and refraction. The investigations suggest that nonlinear absorption and refraction caused by distortion of the electron cloud might be associated with the H2PO4− and (FeO4)2− groups.

The nonlinear refractive index n2 is an important parameter for the nonlinear optical properties of a medium. This study primarily targets to measure the third-order nonlinear optical properties of potassium dihydrogen phosphate (KDP) and deuterated potassium dihydrogen phosphate (DKDP) with 70% deuteration content at λ = 532 nm using the Z-scan technique. The relationship between nonlinear refraction and direction has been studied in detail. Nonlinear refractive index n2, γ and third-order nonlinear susceptibilities xk3 (esu) were calculated through normalized transmittance curves and theoretical formulas. The results indicate that the nonlinear refractive indexes of KDP and DKDP are positive and possess obvious self-focusing effects in high-power laser systems.

Black phosphorous (BP), the most thermodynamically stable allotrope of phosphorus, fills up the lacuna left by other two-dimensional materials with a band gap from 0.3 to 2 eV. The narrow direct band gap and the strong light-matter interaction make BP a promising nonlinear optical (NLO) nano-material. In this paper, the NLO properties of multilayer BP nano-sheets were researched by an open aperture z-scan method. Optical limiting (OL) behavior was observed in the BP material. Three different excitation wavelengths (1064, 532 and 355 nm) were used in the experiments, and the long wavelength excitation exhibited superior NLO performance, including OL and saturable absorption (SA). Our results demonstrate that BP is a promising candidate for OL applications.

The band structure of graphene can be adjusted by incorporating other elements or functional groups, correspondingly, the response to an external light field will also be changed. In this study, we investigated the nonlinear optical (NLO) responses of N-doped graphene nanosheets (N-Gns) with an open aperture Z-scan method, under the excitation of picosecond laser pulses. To the best of our knowledge, this is the first time that two-photon absorption (2PA) of N-Gns has been reported. The normalized nonlinear transmission demonstrates that with the increasing excitation energy, the saturable absorption (SA) and the 2PA appear successively. Compared to the 532 nm excitation, the 1064 nm excitation exhibits smaller saturable intensity Is and larger 2PA coefficient β. At the same time, the N-Gns present superior NLO property compared to pure graphene. Consequently, N-Gns will be a promising candidate for SA or optical limiting (OL) applications.

[(4-Ethoxyanilinum)(18-crown-6)][BF4] (1) single crystals were successfully grown by solution method, with its structure, phase purities, thermal stability, dielectric, absorption and fluorescence spectra were systematically characterized for the first time. The DSC, XRD and dielectric measurements showing that no phase transition occurs in compounds 1 over the temperature ranges of 100–298 K. The absorption edge located in ultraviolet ranges and extended to 300 nm, with strong photoluminescence peak at 296 nm was observed when it was excited at 252 nm by a xenon lamp. All the results make compound 1 promising candidates for optical applications. More importantly, the specific roles of organic and inorganic components of crown compounds were preliminary determined by comparison, which have guiding significance in searching for new compounds with some interesting performances.

For rapid growth of KDP crystal, the influence of agitation intensity on solution stability was investigated by altering rotation speed in crystalline procedure. Based on the experiments, the results demonstrate that rotation speed has a great influence on growth rate, which increases with increase of rotation speed as is no more than 100 r/min. The corresponding metastable zone widths (MSZW) indicate that solution stability decreases with the agitation intensity increasing, while introducing a seed into the growing solution has little effect on MSZW. Combined with numerical simulation, the dependences of rotation speeds on turbulent dissipation and vorticity imply that growth solution with a laminar state has a better stability and a stronger ability to resist spontaneous crystallization at lower speeds. With increasing of rotation speeds ranging from 22 to 106 r/min, the growth solution is transformed from laminar to turbulent state causing the decrease of solution stability, while the turbulent dissipation rate increases gently with increasing of rotation speed. Furthermore, the vortex magnitude increases with rising of rotation speed, and an obvious variation of vorticity has a substantial impact on solution instability, especially at high-speed larger than 200 r/min. Thus, appropriately reducing speed is an effective way to maintain the stability of growing environment and beneficial to realize rapidly grown KDP crystal with high-quality.

For rapidly grown KDP crystal, the whole growth zone is composed of prismatic- and pyramidal-sector. In order to further understand the distinctions between them, KDP crystals doped with Fe3+ in trace amount were selected to explore the influences of metal cation with high-valence on growth characteristics, Optical quality and nonlinear refraction. The growth characteristics for as-grown crystals indicate that the growth rate of prismatic sector can be obviously inhibited by Fe3+ ions with less than 15 ppm due to the stronger electronegativity of (100) face. With the increase of Fe3+, the crystal and optical qualities show significantly lower trends, especially for the prismatic sector. The influence of Fe3+ ions on nonlinear refraction was observed by Z-scan technique, which shows that self-focusing effect could be caused in high-intensity laser system because of the nonlinear refractive index obtained with a positive sign. Specially, nonlinear refraction effects along II-type and z-cut in prismatic area both show a significant variation with increase of Fe3+, while a negligible effect on nonlinear refraction is proved for pyramidal sector. Additionally, the generation of nonlinear refraction is mainly attributed to the electron-cloud distortion of H2PO4− groups, and the changes in prismatic sector may be due to the existence of (FeO4)2- groups.

Organic–inorganic hybrid new crystals, [(parachloroanilinum+)(18-crown-6)][ClO4−](CH3COCH3) and [(parachloroanilinum+)(18-crown-6)][BF4−](CH3COCH3), with high phase transition temperatures and noncentrosymmetric structures were grown. Their physical properties, including their structures, phase transitions, and dielectric, piezoelectric and photoluminescent properties, were systematically investigated. A phase transition at 71 °C was successively detected and confirmed by DSC and dielectric measurements. Piezoelectric features were clearly verified by piezoresponse force microscopy. Both compounds show strong and wide photoluminescent properties. All the results make the two compounds promising candidates for potential applications in the piezoelectric and optical fields.

Nonlinear optical absorption of fluorine-functionalized graphene oxide (F-GO) solution was researched by the open-aperture Z-scan method using 1064 and 532 nm lasers as the excitation sources. The F-GO dispersion exhibited strong optical limiting property and the fitted results demonstrated that the optical limiting behavior was the result of a two-photon absorption process. For F-GO nanosheets, the two-photon absorption coefficients at 1064 nm excitation are 20% larger than the values at 532 nm excitation and four times larger than that of pure GO nanosheets. It indicates that the doping of fluorine can effectively improve the nonlinear optical property of GO especially in infrared waveband, and fluorine-functionalized graphene oxide is an excellent nonlinear absorption material in infrared waveband.

Nonlinear optical absorption effect in KDP and 70%-DKDP crystals, which were grown by the conventional temperature cooling method, was systematically studied using picosecond pulse laser excitation. Using open aperture Z-scan measurements, the dependence of nonlinear absorption effect on sample orientations (I, II, and z) as well as laser intensity was systematically measured at λ = 1064 and 532 nm. According to the experimental results, the nonlinear absorption effect at λ = 532 nm was confirmed, while at λ = 1064 nm no nonlinear absorption was observed for KDP and 70%-DKDP crystals. In addition, the optical absorption along I- and II-type affected by laser intensity was larger than that along the z-direction. The important nonlinear absorption coefficients β and χ I ( 3 ) (esu) measured along different orientations were exhibited in detail at wavelengths of 1064 nm and 532 nm. The results indicate that nonlinear absorption coefficients increase first and then decrease with the increment of laser intensity for KDP and 70%-DKDP crystals.

A series of K(D x H1− x )2PO4 (DKDP; x = 0, 12, 70, and 80%) crystals were grown using the point-seed technique. A positive nonlinear refractive index is exhibited, implying a self-focusing effect. The nonlinear refraction along the z-direction is greater than that along the II-direction, indicating that the distribution of the H2PO4 − and D2PO4 − groups have a critical influence on the nonlinear refraction. The nonlinear refraction effect of "point-seed" crystals is greater than that of traditional growth crystals, demonstrating that the crystalline quality is a major factor. Compared to the pyramid region, the prism region has a larger nonlinear refraction effect. The vital parameters n 2 and have been calculated and the results allow for DKDP applications.

In this work, using large-sized single crystals of high optical quality, the optical properties of Ba2TiSi2O8 were systematically investigated, including transmission spectra, refractive indices and nonlinear absorption properties. The crystal exhibits a high transmittance (>84%) over a wide wavelength range from 340 to 2500 nm. The refractive indices in the range from 0.31256 to 1.01398 μm were measured, and Sellmeier’s equations were fitted by the least squares method. The nonlinear absorption properties were studied by using the open-aperture Z-scan technique, with a nonlinear absorption coefficient measured to be on the order of 0.257 cm/GW at the peak power density of 16.4 GW/cm2. Such high transmittance and wide transparency indicate that optical devices using the Ba2TiSi2O8crystal can be applied over a wide wavelength range. Furthermore, the small nonlinear absorption observed in Ba2TiSi2O8 will effectively increase the optical conversion efficiency, decreasing the generation of laser damage of the optical device.

High-quality KDP and DKDP crystals with 12%, 70% and 80%-deuterium content were grown by the conventional temperature cooling method. The nonlinear optical characteristics of K(DxH1-x)2PO4 crystals, including nonlinear absorption and refraction, were systematically investigated through the Z-scan method at λ = 532 nm. The results demonstrate the existence of nonlinear absorption and refraction, and a nonlinear refractive index with a positive sign indicates the generation of self-focusing effect. Moreover, the results indicate that nonlinear absorption and refraction were associated with crystal direction and structure, especially the distribution of H2PO4 - or D2PO4 - groups. For K(DxH1-x)2PO4 crystals, a similar rule of β was z > I > II, while n2 (or χR(3)) was z > II ≈I. These results will evoke more attention to KDP and DKDP applications, especially frequency conversion and electro-optic switch.

Large Ba2TiSi2O8 crystals were successfully grown by the Czochralski technique. The stimulated Raman scattering properties of the Ba2TiSi2O8 crystals were investigated for the first time, and the first (558 nm) and second (587 nm) Stokes lines were generated in an ultracavity single-pass configuration excited by 532 nm picosecond pulses. The output energy and conversion efficiency of the scattering process as functions of pump energy were studied, and the highest conversion efficiency was found to be 31.8%. The experiments indicate that Ba2TiSi2O8 is a novel active crystal suitable for solid-state Raman laser applications.