Femtosecond Z-scan measurements of nonlinear refraction in nonlinear optical crystals

We report an investigation of third-order optical nonlinearities in several nonlinear optical crystals using the Z-scan technique with femtosecond laser pulses at 780 nm wavelength. The crystals studied include LiNbO₃:MgO, KTiOAsO₄, KTiOPO₄, β-BaB₂O₄ and LiB₃O₅, which are extensively used for ultrashort-pulse second-harmonic generation and optical parametric oscillation. The nonlinear refractive index n₂ in these crystals has been determined to be in the range from 10⁻¹⁶ to 10⁻¹⁵ cm²/W. No two-photon absorption has been observed. The experimental results are compared with the two-band model for the bound electronic Kerr nonlinearity. It is shown that the measured n₂ values in β-BaB₂O₄ and LiB₃O₅ are one order of magnitude smaller than those of LiNbO₃:MgO, KTiOAsO₄, KTiOPO₄, which is in agreement with the theoretical prediction.     

Anisotropy of inter-band transitions and band structure of Cs3Zn6B9O21 nonlinear optical crystals

Polarized optical functions near the fundamental absorption edge of novel Cs₃Zn₆B₉O₂₁ nonlinear optical crystals possessing a wide UV transparency down to 190 nm were investigated. The anisotropy of optical functions is not well studied yet which restrains the further strategy of the formation on its base of solid state compounds with desirable properties. The studies were performed using a band structure calculations as well as the experimental measurements of fundamental polarized UV absorption edge and X-ray photoelectron spectra of the studied crystals. The experimental data were used for evaluation of scissor factors of the band structure. The results of the calculations were compared with the XPS and polarized absorption optical spectra of the investigated crystals. The introduction of the scissor factor was performed in order to obtain a sufficient agreement with experiment. The observed anisotropy of absorption may be explained by the anisotropy of carrier effective masses.     

Growth and characterization of some novel crystals for nonlinear optical applications

The advent of high intensity lasers coupled with the recent advances in crystal technology has led to rapid progress in the field of nonlinear optics. This article traces the history of materials development that has taken place over the past forty odd years and dwells on the current status in this important area. The materials aspect is discussed under three classes viz. inorganic, organic and semiorganic crystals. In the end, some of the crystal growth work that has been carried out in author’s laboratory is presented.     

Growth and characterization of Ca5(BO3)3F fiber crystals, a new nonlinear optical material for UV light generation

For the first time, Ca₅(BO₃)₃F (CBF) fiber crystals were grown by the micro-pulling down technique from LiF-based flux. Regular and transparent fibers were obtained with good optical quality. Characterization by Raman spectroscopy and EDX microprobe showed fibers compositionally homogeneous. The specific heat capacity of the fibers was measured indicating a laser damage threshold slightly lower, at room temperature, than for crystals belonging to the related rare earth calcium oxoborate family.     

Optical bistability in BaTiO3

In this paper experimental results concerning the optical bistability of a ferroelectric monocrystal of BaTiO₃ are presented. Two laser beams were used to interact with the monocrystal which resulted in the bistability of the intensity of the transmitted wave. This was achieved without the application of any optical resonator. The feedback was provided by the electronic system through a mechanism typical to all photorefractive materials.     

Crystallization kinetics and high-resolution X-ray diffraction analysis on nonlinear optical l-threonine single crystals

Crystallization parameters such as critical radius, critical free energy and volume free energy change have been evaluated for l-threonine single crystals using homogeneous nucleation theory. Metastable zone width and induction period measurements have been carried out experimentally. Interfacial energy values for the aqueous solution of l-threonine were also calculated from the solubility data. Optimization of growth parameters has been tried for bulk crystal growth and it has been discussed in detail. The crystalline quality of the bulk samples grown at different pH values have been tested by high-resolution X-ray diffraction analysis.     

Optical and nonlinear optical properties of orthorhombic BiB3O6

Dispersion of refraction coefficients of orthorhombic BiB₃O₆ in the wavelength range between 435.8 and 1060 nm is studied, nonlinear optical coefficients are determined, and phase matching angles, angular and spectral bandwidths for second harmonic generation processes are calculated. δ-BiBO may be suitable for doubling of lasers with a wavelength in the 1.3 μm region as well as the matrix for self-doubling lasing media.     

Growth,optical and microstructural properties of PbB4O7 plate crystals

Centimeter-sized optical quality plate-like PbB₄O₇ crystals have been grown by Czochralski method. The fundamental absorption edge has been found at 237 nm (corresponding bandgap 5.75 eV) with the distinct sideband protruding up to 300 nm. The crystals are well faceted with the (1 0 0), (0 1 0) and (1 0 1) planes, (1 0 0) surfaces being mostly developed. The etching in diluted nitric acid (5 wt.%) at the temperature of 90 °C have been used to reveal the defect structure and remove melt residuals. The (1 0 0) surface shows the presence of etching pits and twin boundaries. The Kikuchi line pattern and developed microrelief with the roughness of ∼8 nm have been observed by RHEED and AFM, respectively.     

Nonlinear optical properties of some derivatives of stilbene and vinyl cyanide

Three derivatives of stilbene: 3-hydroxy-4-methoxy-4^′-nitrostilbene (HMONS), 3-methoxy-4-hydroxy-4^′-nitro-stilbene (MOHNS), 2-cyano-3-indole-propenoic acid ethyl ester (CIP-ethyl), and one derivative of vinyl cyanide: p-1,1-dicyano-vinyl-dimethylaminoaniline (DVDA) were designed and synthesized. The powder second-harmonic generation and absorption spectra of these four compounds were measured. First principle calculation of the molecular first hyperpolarizabilities of HMONS were calculated and compared with those of 3-methyl-4-methoxy-4^′-nitrostilbene (MMONS, Appl. Phys. Lett. 56 (1990) 423) in order to elucidate their structural origin of the optical nonlinearity.     

Modification of UV-VIS optical absorption properties caused by MgO incorporation in MgO-doped LiNbO3 crystals

MgO-doped LiNbO₃ single crystals were investigated in the UV-VIS range to study the effect of MgO in the LiNbO₃ host. Congruent LiNbO₃ has an optical absorption edge of 3.75 eV. Analysis of the absorption edge gave an estimate of the indirect band gap for MgO-LiNbO₃ solid solutions. The band gap shows an MgO threshold effect in the absorption coefficient. An additional indirect transition at 2.2–2.5 eV was revealed when MgO was incorporated into the lithium niobate structure. This indirect transition also has a MgO threshold effect around 5 mol% MgO.     

Linear and nonlinear optical properties of organic crystals: MBANP and its derivatives

In addition to possessing strong optical nonlinearity, the (−)-2-(α-methylbenzylamino)-5-nitropyridine (MBANP) crystal has been shown to have unusual linear optical properties. Two methyl derivatives of MBANP have now been synthesized and grown as large single crystals; their refractive indices have been measured as a function of frequency and second-harmonic generation, including the determination of the phase matching loci has been investigated. Data is also available on the racemic form of crystalline MBANP. The properties of this family of crystals have been reviewed and an attempt is made to relate the experimental responses of the crystals to their molecular structure and the calculated properties of the molecules.     

Temperature-dependent Sellmeier equations of nonlinear optical crystal Na3La9O3(BO3)8

The principal refractive indices of Na₃La₉O₃(BO₃)₈ (NLBO) crystal in the wavelength range of 0.363–2.325 μm were accurately measured by using the minimum deviation method within the temperature range from 23.5 °C to 160 °C. We derived the expressions of thermal refractive index coefficient as a function of wavelength that could be used to calculate the principal refractive indices at different wavelengths. The temperature-dependent Sellmeier equations were also derived and used to calculate the phase-matching (PM) angles for a frequency conversion device based on NLBO crystal at different temperatures. We found that the thermal refractive index coefficients of NLBO crystal changed from positive to negative values with the increase of wavelength. In addition, the phase matching conditions for third harmonic generation (THG) at different temperatures were also investigated.     

Tuning the dielectric properties of thiourea analog crystals for efficient nonlinear optical applications

Materials with low dielectric constant have attracted a great deal of interest in the field of nonlinear applications and microelectronic industry. Metal complexes of thiourea with group II transition metals (Zn, Cd) as central atom and period III elements (S, Cl) were synthesized by chemical reaction method and single crystals were grown from aqueous solution by slow evaporation method. By parallel plate capacitor technique, the dielectric response, dissipation factor, ac conductivity and impedance of virgin and metal complexes have been studied in the frequency (100 Hz to 5 MHz) and temperature (303-423 K) ranges. Metal complexes of thiourea with cadmium substitute have a low dielectric constant less than 10. Also the presence of chlorine in the metal complex induces noncentro symmetric structure. Hence the role of group II transition metals and period III elements in tuning the dielectric properties for efficient nonlinear applications has been studied.     

Synthesis and nonlinear optical properties of Lead Telluride nanorods

Lead Telluride (PbTe) nanorods have been uniformly grown on silicon substrates, using the thermal evaporation technique under high vacuum conditions. The structural and morphological studies are done using X-ray diffraction and scanning electron microscopy. Optical nonlinearity studies using the open aperture z-scan employing 5 ns and 100 fs laser pulses reveal a three-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (γ) are in the order of 10⁻²² m³ W⁻² and for femtosecond excitation it is in the order of 10⁻²⁹ m³ W⁻². The role of free carriers and excitons in causing the nonlinearity in both excitation time domains is discussed. Results indicate that PbTe nanorods are good optical limiters with potential device applications.     

纯介质光子晶体非线性效应研究进展

如何在低阈值小尺度(毫瓦或皮焦量级、微米以下)情况下激发非线性光学效应是近年来光学领域研究的重要课题。该研究最直接的应用需求就是光子集成芯片,这是未来实现超高速、大容量信息网络体系的基础。光子晶体具有类似于半导体能带的光子禁带(PBG),被誉为“光子半导体”,为人们提供了一种新颖而又实用的操纵光子的物理手段,使低阈值、可集成非线性效应产生成为可能。越来越多的非线性效应在光子晶体中已经被发现,例如光子晶体慢光、带隙孤子、电磁感应透明、二次谐波产生、光学双稳态等,本文将着重对可用于光子集成器件开发的光子晶体非线性效应研究领域的一些主要成果和进展进行总结,介绍其相关应用并对光子晶体非线性效应研究作出展望。

     

Effect of incorporation of titanium dioxide nanocrystals on bulk properties of KDP crystals

The impact of titanium dioxide (anatase) nanocrystals on growth process, optical and structural properties of KDP single crystal was studied. As-grown crystals were characterized by High Resolution Three-crystal X-ray Diffractometer, optical diagnostics of elastic scattering, cone-shaped interference method, and spatial profile analysis method. In the composite system KDP:TiO₂ the effect of giant nonlinear optical response of anatase nanoparticles was revealed, in particular in the intensity range up to 20 MW/cm² the change of sign of the nonlinear refraction index was found. These results can be explained by the resonance excitation of defective states on TiO₂ nanoparticle surface.     

Linear and nonlinear optical properties of borate crystals as calculated from the first principles

With the development of the state-of-the-art band calculation scheme and massively parallel processing in the high performance computing, we are now able to calculate all important physical properties, including (i) the nonlinear susceptibility; (ii) the multiphoton absorption rate; (iii) the birefringence; and (iv) the energy gap, from the first principles for complex practical nonlinear optical crystals, such as the borate crystal series, with an accuracy acceptable for materials development/design, and answer the questions often raised by the material scientists.     

Second-order nonlinear optical properties of mexylaminotriazine-functionalized glass-forming azobenzene derivatives

The second-order nonlinear optical coefficients of thin films of mexylaminotriazine-functionalized azobenzene molecular glass derivatives were measured using second harmonic generation. The thin films were poled using a custom corona poling set-up and the second harmonic light from a pulsed 1064-nm laser was detected. Four out of the six tested compounds showed optical nonlinearity and a maximum coefficient of 75 pm/V was obtained. The time dependence of the nonlinear coefficients was studied under ambient light and under dark; the second harmonic generation intensity stayed constant for thiazole-containing derivatives while a significant decay was measured for the other compounds.     

Growth and characterization of dexterous nonlinear optical material: Dimethyl amino pyridinium 4-nitrophenolate 4-nitrophenol (DMAPNP)

The crystals (dimethyl amino pyridinium 4-nitrophenolate 4-nitrophenol [DMAPNP] suitable for NLO applications were grown by the slow cooling method. The solubility and metastable zone width measurement of DMAPNP specimen was studied. The material crystallizes in the orthorhombic crystal system with noncentrosymmetric space group of P2₁2₁2_1. The ocular precision in the intact visible region was found to be good for non-linear optical claim. Quality of the grown crystal is ascertained by the HRXRD and etching studies. Laser Damage Threshold and Photoluminescence studies designate that the grown crystal contains less imperfection. The mechanical behaviour of DMAPNP sample at different temperatures was investigated to determine the hardness stability of the grown specimen. The piezoelectric temperament and the relative Second Harmonic Generation (for diverse particle sizes) of the material were also studied. The third order nonlinear optical properties of DMAPNP crystals were premeditated by Z-scan method. Birefringence and optical homogeneity of the crystal were evaluated using modified channel spectrum method. The half wave voltage of the grown crystal deliberate from the elector optic experimentation. Photoconductivity measurement specified consummate of inducing dipoles owing to brawny incident radiation and also disclose the nonlinear activities of the grown specimen.     

Growth and optical properties of (Yb3−xYx)Al5O12:Ce single crystals

To improve the infrared emission of Yb³⁺ ions doped in the garnet host Y₃Al₅O₁₂ (YAG) single crystal through the energy transfer from Ce³⁺ to Yb³⁺ ions, the 〈1 1 1〉-oriented YAG:Ce³⁺, YAG:Yb³⁺, YAG:(Ce³⁺, Yb³⁺) and Yb₃Al₅O₁₂:Ce³⁺ (YbAG:Ce³⁺) single crystals were grown using the Czochralski Method, respectively. The excitation and emission spectra of these garnet single crystals were characterized. In YAG:Ce³⁺ crystal, the yellow emission of Ce³⁺ ions present, but it was completely extinguished in YAG:(Ce³⁺, Yb³⁺) crystal and YbAG:Ce³⁺ crystal. However, the characteristic absorption bands of Ce³⁺ still existed in the excitation spectrum of Yb³⁺ ions, which showed that the energy absorbed by Ce³⁺ ions can be transferred to Yb³⁺ ions for its infrared emission.