Na6 MQ4 (M=Zn, Cd; Q=S, Se): Promising New Ternary Infrared Nonlinear Optical Materials.

Four sodium-based ternary IR nonlinear optical (NLO) materials, Na6 MQ4 (M=Zn, Cd; Q=S, Se), were prepared through a high-temperature flux method. The crystal structure of the compounds is built up of isolated [MQ4 ] tetrahedra and a 3D framework formed by the NaQn (n=4, 5) units. The two selenides, Na6 MSe4 (M=Zn, Cd), as promising IR NLO materials, show moderate second-harmonic generation (SHG) responses (0.9 and 0.5×AgGaS2 ) with good phase-matching behavior, as well as high laser damage thresholds (2 and 1.9×AgGaS2 ). The two sulfides, Na6 MS4 (M=Zn, Cd), exhibit higher laser damage thresholds (13 and 4×AgGaS2 ), but smaller SHG responses (0.3 and 0.2×AgGaS2 ). Theoretical calculations and statistical analyses indicate that the SHG effect and band gap in the compounds originate mainly from the distorted NaQ4 NLO-active units with a short Na-S bond length, which provides a new insight into the design of novel IR NLO materials.

Li2 MTeO6 (M=Ti, Sn): Mid-Infrared Nonlinear Optical Crystal with Strong Second Harmonic Generation Response and Wide Transparency Range.

Oxide crystals have been widely used in nonlinear optics (NLO) in the ultraviolet-visible and near-infrared regions. Most traditional oxide crystals are restricted to the mid-infrared region due to their narrow transmission window. Hence, attempting to extend infrared cutoff wavelength of oxides has attracted much attention. Herein, we report two new tellurates Li2 TiTeO6 (LTT) and Li2 SnTeO6 (LST) with broad transparent regions of 0.38-6.72 and 0.38-6.86 µm, respectively, as excellent candidates for mid-infrared NLO applications. Both LTT and LST crystallize in the orthorhombic space group Pnn2. The LTT crystal exhibits intense powder second-order generation efficiency (26×KDP) under the fundamental wavelength of 1064 nm. First-principles calculations and dipole moments were used to illustrate the results of the powder second-harmonic generations based on the crystal structures. Our results provide a novel oxide NLO crystal with a strong SHG and wide transparency range. They also pave a way for the design of new oxide mid-IR NLO crystals.

Design of a High-Efficiency Multilayer Dielectric Diffraction Grating with Enhanced Laser Damage Threshold.

Diffraction gratings are becoming increasingly widespread in optical applications, notably in lasers. This study presents the work on the characterization and evaluation of Multilayer Dielectric Diffraction Gratings (MDG) based on the finite element method using Comsol MultiPhysics software. The optimal multilayer dielectric diffraction grating structure using a rectangular three-layer structure consisting of an aluminum oxide Al2O3 layer sandwiched between two silicon dioxide SiO2 layers on a multilayer dielectric mirror is simulated. Results show that this MDG for non-polarized lasers at 1064 nm with a significantly enhanced -1st diffraction efficiency of 97.4%, reaching 98.3% for transverse-electric (TE) polarization and 96.3% for transverse-magnetic (TM) polarization. This design is also preferable in terms of the laser damage threshold (LDT) because most of the maximum electric field is spread across the high LDT material SiO2 for TE polarization and scattered outside the grating for TM polarization. This function allows the system to perform better and be more stable than normal diffraction grating under a high-intensity laser.

Optimizing the Nonlinear Optical Performance of an A-N-M-Q (A: Alkali Metal; N: d10 Metal; M: Main Group Metal; Q: Chalcogen) System.

Exploring new infrared nonlinear optical (IR NLO) materials with superior overall properties is scientifically and technically important. However, large second-order harmonic generation (SHG) efficiencies and high laser-induced damage thresholds (LIDT) are incompatible, which makes realizing this goal a challenge. The IR NLO performance of an A-NIIB-MIIIA-Q (Q: chalcogen) system was optimized by simultaneously modulating A/(M + N) and M/N ratios (A: alkali metal; N, M: tetra-coordinated metals), and SHG-LIDT balance was achieved. Three new sulfides, KCd3Ga5S11 (1), RbCd4Ga3S9 (2), and Cs2Cd2Ga8S15 (3), containing the same CdS4 and GaS4 but with different A/(Ga + Cd) and Ga/Cd ratios were obtained. Among these compounds, compound 3 exhibits both the largest SHG efficiency (0.5 × AgGaS2) and LIDT (35 × AgGaS2), which can be ascribed to the Ga/Cd modulation for enhancing the NLO functional motif distortions and SHG efficiency as well as the A/(Ga + Cd) modulation for enlarging the band gap and LIDT. Remarkably, compound 3 is the first phase-matchable IR NLO material in the A-NIIB-MIIIA-Q family. This article proposes a novel avenue to explore infrared nonlinear materials with superior comprehensive properties by modulating the A/(M + N) and M/N ratios.

Effect of NaCl on the properties of sulphamic acid single crystals.

Single crystals of pure and NaCl doped sulphamic acid (SA) were grown by slow evaporation method at room temperature. The lattice parameters and structure were determined by using single crystal and powder X-ray diffraction analyses. The presence of dopant in the SA lattice was affirmed by EDAX analysis. UV-Vis spectra show maximum transmittance in the visible region. The band gap energies were found to be 6.06 eV and 5.70 eV for pure and NaCl doped SA crystals respectively. From the PL specta the emission were observed at 335 and 424 nm for pure and 340 and 428 nm for doped SA crystal. The thermal stability of the grown crystals were analyzed by thermogravimetric and differential thermal analysis (TGA/DTA) and revealed that the grown crystals were thermally stable up to 331 °C and 334 °C for pure and NaCl doped SA. Vickers microhardness study reveals that the hardness of the crystals is increase with increasing load. The photoconductivity study shows that the grown crystals are negative photoconductive nature. The Laser Damage Threshold (LDT) indicates the grown crystals have good resistance to laser radiation than a standard Potassium dihydrogen phosphate (KDP) crystal. The Z-scan technique was employed to determine the nonlinear refractive index, nonlinear optical absorption and third order nonlinear optical (TONLO) susceptibility of the grown crystals using He-Ne laser.

Crystal property and spectroscopic investigation on electro-optic and physico-chemical properties of NLO crystal; 3-(3,4-Dihydroxyphenyl)-L-Alanine.

In this attempt, in order to obtain high-quality NLO crystal, organic compound; 3-(3,4-Dihydroxyphenyl)-L-Alanine crystal was fabricated. The organic-composite crystal was characterized by crystallographic and spectroscopic tools. The NLO supported parameters like crystal lattice (orthorhombic) and space group (P212121) examined and validated by XRD examination. The SHG test was carried out and SHG efficiency was calculated that1.29 and 1.35 times greater than solid KDP crystal. The laser damage threshold energy density was determined to be 14.51 GW/cm2. By the application of mulliken charge assignment, multiple dielectric cavities were found in crystal material which is able to process the high degree of birefringence gradient. The oscillating chemical potential movement was observed by examining chemical shift, among the core carbons of hexagonal ring and bridge carbons of chain. The chemical softness insists the binding viability of further ligand groups. The π and δ-conjugated interactive complex orbitals recognized on molecular site and participation in optical active mechanism was identified. UV-Visible transmission characteristics of crystal were studied and UV-Visible absorption on degenerate energy states was noted and its band gap energy was estimated. The CT complex of the present case was acknowledged to be COOH group and it causing crystal properties of current organic composite. The hyperactive polarizability was determined as 1775.05 × 10-33 esu and it was found to be five times greater than thiourea. The depletion energy between highly electrophilic zones and protonic zones was estimated to be ±5.241 e 2 causing permanent dielectric characteristics for the title organic composite. The non-superposable on the molecular mirror image was displayed and thereby optical ability was validated.

Excellent Infrared Nonlinear Optical Crystals BaMO(IO3)5 (M = V, Ta) Predicted by First Principle Calculations.

Two nonlinear optical crystals, BaVO(IO3)5 and BaTaO(IO3)5, are designed by substituting Nb with V and Ta, respectively, in BaNbO(IO3)5, which is itself a recently synthesized infrared nonlinear optical (NLO) material. The designs of BaVO(IO3)5 and BaTaO(IO3)5 from BaNbO(IO3)5 are based on the following motivation: BaVO(IO3)5 should have a larger second-harmonic generation (SHG) coefficient than BaNbO(IO3)5, as V will result in a stronger second-order Jahn-Teller effect than Nb due to its smaller ion radius; at the same time, BaTaO(IO3)5 should have a larger laser-damage threshold, due to the fact that Ta has a smaller electronegativity leading to a greater band-gap. Established on reliable first-principle calculations, it is demonstrated that BaVO(IO3)5 has a much larger SHG coefficient than BaNbO(IO3)5 (23.42 × 10-9 vs. 18.66 × 10-9 esu); and BaTaO(IO3)5 has a significantly greater band-gap than BaNbO(IO3)5 (4.20 vs. 3.55 eV). Meanwhile, the absorption spectra and birefringences of both BaVO(IO3)5 and BaTaO(IO3)5 are acceptable for practice, suggesting that these two crystals can both be expected to be excellent infrared NLO materials.

Growth, crystalline perfection, spectral and optical characterization of a novel optical material: l-tryptophan p-nitrophenol trisolvate single crystal.

l-tryptophan p-nitrophenol trisolvate (LTPN), an organic nonlinear optical material was synthesized using ethanol-water mixed solvent and the crystals were grown by a slow solvent evaporation method. The crystal structure and morphology were studied by single crystal X-ray diffraction analysis. The crystalline perfection of the LTPN crystal was analyzed by high-resolution X-ray diffraction study. The molecular structure of the crystal was confirmed by observing the various characteristic functional groups of the material using vibrational spectroscopy. The cut-off wavelength, optical transmission, refractive index and band gap energy were determined using UV-visible data. The variation of refractive index with wavelength shows the normal behavior. The second harmonic generation of the crystal was confirmed and the efficiency was measured using Kurtz Perry powder method. Single and multiple shot methods were employed to measure surface laser damage of the crystal. The photoluminescence spectral study revealed that the emission may be associated with the radiative recombination of trapped electrons and holes. Microhardness measurements revealed that LTPN belongs to a soft material category.

Synthesis, crystal growth and characterization of an organic material: 2-Aminopyridinium succinate succinic acid single crystal.

The 2-aminopyridinium succinate succinic acid (2APS) single crystal was synthesized and grown by slow evaporation method. The crystal structure has been confirmed by powder X-ray diffraction as well as single crystal X-ray diffraction analysis. The crystal perfection has been evaluated by high resolution X-ray diffraction (HRXRD). The grown crystal is transparent in the visible and near infrared region. The optical absorption edge was found to be 348 nm. The fluorescence study was carried out by spectrofluorophotometer. The thermal stability of grown crystal was analyzed by thermal gravimetric and differential thermal gravimetric (TG-DTA) analysis. Vicker's hardness study carried out at room temperature shows increased hardness while increasing the load. Laser damage threshold value was determined by Nd:YAG laser operating at 1064 nm. The grown 2APS crystal was characterized by etching studies using water as etchant.

Crystal growth, spectral, optical, laser damage, photoconductivity and dielectric properties of semiorganic L-cystine hydrochloride single crystal.

The semiorganic single crystals of l-cystine hydrochloride have been grown by slow evaporation solution growth technique at 40°C. The grown crystals were subjected to single crystal XRD, FTIR, optical absorbance, laser damage threshold, photoluminescence, photoconductivity and dielectric studies. Single crystal XRD studies reveal that the crystal belongs to monoclinic system with space group C2 and the lattice parameters are a=18.63 (Å), b=5.28 (Å), c=7.26 (Å), α=90°, ß=103.70°, γ=90° and V=696 (Å(3)). FTIR spectroscopy confirms that a band at 1731 cm(-1) represents characteristic of α-amino acid hydrochlorides. The UV-Vis-NIR absorption spectrum was analyzed and the optical band gap energy was found to be 3.8eV. The crystal exhibits sharp emission peak at 388 nm. The thermal characteristics of crystals were studied by TG-DTA, which indicate that there is no weight loss up to 201°C. Surface laser damage threshold value of title compound was estimated using high power Q-switched Nd:YAG laser operating at 1064 nm. Dielectric and photoconductivity studies were also carried out for the grown crystals.

A study on Fourier transform infrared spectroscopy, thermal, mechanical, NLO and laser damage properties on unidirectional Glycinium Picrate Mono Glycine crystal.

By directional solidification, single crystal of Glycinium Picrate Mono Glycine (GPMG) was successfully grown by Sankaranarayanan-Ramasamy (SR) method. An optically transparent crystal of GPMG has been grown along 〈011〉 plane by a mixed solvent of acetone and double distilled water. The evaporation rate was controlled and a single crystal of 12mm diameter and 35mm length was obtained. Single crystal X-ray diffraction, Fourier Transform Infrared Spectroscopy (FTIR), thermal, mechanical, SHG and laser damage studies were carried out. The results are discussed in detail.