Efficient Nonlinear Optical Crystals Research Articles

Design Strategy of Highly Efficient Nonlinear Optical Orange‐Colored Crystals with Two Electron‐Withdrawing Groups

A new class of highly efficient nonlinear optical organic salt crystals is reported. In nonlinear optics based on organic materials, it is well known that using two electron‐withdrawing groups (EWGs) onto cationic electron acceptors instead of conventional one EWG remarkably enhances microscopic optical nonlinearity for chromophores. However, the corresponding organic crystals possessing enhanced large macroscopic optical nonlinearity have not been reported yet. Herein, a design strategy is proposed for obtaining highly efficient nonlinear optical crystals based on two EWGs in cationic electron acceptors. Introducing a phenolic electron donor, promoting a head‐to‐tail interionic assembly, along with a two‐EWG N‐pyrimidinyl pyridinium electron acceptor in cationic chromophores results in a preferred non‐centrosymmetric, perfectly parallel alignment of chromophores in crystal. Newly designed OPR (4‐(4‐hydroxystyryl)‐1‐(pyrimidin‐2‐yl)pyridinium) crystals exhibit approximately two times larger effective first hyperpolarizability than that of analogous N‐alkyl OHP (4‐(4‐hydroxystyryl)‐1‐methylpyridinium) crystals based on only one EWG. OPR crystals exhibit comparable second‐order optical nonlinearity to benchmark red‐colored DAST (4‐(4‐(dimethylamino)styryl)‐1‐methylpyridinium 4‐methylbenzenesulfonate) crystals, but a significant blue‐shifted absorption resulting in orange‐color crystals. Therefore, phenolic organic salt crystals using two EWGs are highly promising materials for various nonlinear optical applications.

Recent progress in acentric core structures for highly efficient nonlinear optical crystals and their supramolecular interactions and terahertz applications

During the past decade, various new types of organic nonlinear optical crystals have been developed to overcome the benchmark stilbazolium DAST (4-(4-(N,N-dimethylamino)styryl)-1-methylpyridinium 4-methylbenzenesulfonate) crystal. Here, we review the acentric core structures used in recently developed organic nonlinear optical crystals exhibiting high macroscopic second-order optical nonlinearity, along with their supramolecular interactions and THz applications. The nonlinear optical acentric core structures such as neutral CLP (configurationally locked polyene based on phenyltriene), ionic pyridinium-based N-alkyl DAS (4-(4-(N,N-dimethylamino)styryl)-1-alkylpyridinium benzenesulfonate) and N-phenyl DAP ((4-(N,N-dimethylamino)styryl)-1-phenylpyridinium hexafluorophosphate), ionic quinolinium-based HMQ (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium benzenesulfonate) and OHQ (2-(4-hydroxystyryl)-1-methylquinolinium benzenesulfonate) and benzoindolium-based DBI (2-(4-(dimethylamino)styryl)-1,3,3-trimethyl-3H-benzo[g]indolium iodide) exhibit comparable or enhanced physical properties compared to DAST crystals. Organic crystals introducing an identical acentric core structure often exhibit similar molecular alignment features with analogous supramolecular interactions. We also discuss the nonlinear optical properties and potential applications of these materials, in particular their very promising THz photonic applications.

Studies on the electrical, linear and nonlinear optical properties of Manganese mercury thiocyanate bis-dimethyl sulfoxide, an efficient NLO crystal

Abstract Manganese mercury thiocyanate bis-dimethyl sulfoxide (MMTD), a novel organo-metallic nonlinear optical (NLO) crystal, was grown by a slow evaporation technique over a period of 30 days. The grown crystal was subjected to single crystal X-ray diffraction to determine the unit cell parameters. The optical properties of MMTD were investigated by UV–Vis–NIR, FTIR and FT-Raman spectroscopic techniques. The second harmonic generation (SHG) efficiency of the sample was measured using a Q-switched, mode-locked Nd:YAG laser and the results were compared with urea and manganese mercury thiocyanate (MMTC). The thermal parameters, such as the thermal diffusivity ( α ), thermal effusivity ( e ), thermal conductivity ( k ) and heat capacity ( c p ) of MMTD were measured by the photopyroelectric (PPE) technique and the results are discussed. The dielectric response and mechanical properties of MMTD have also been investigated and reported.

Magnetic and optical phenomena in nonlinear optical crystals ZnGeP2 and CdGeP2

One of the top efficient nonlinear optical crystals, ZnGeP2, is being used at present in parametric oscillators and second-harmonic and combination frequency generators for the mid-IR spectral range. Until recently, this crystal has not been thought of as a magnetic medium, and strong magnetic phenomena were assumed to not occur in it. The recent discovery of a new magnetically ordered state in ZnGeP2 and CdGeP2 single crystals and films doped with Mn shows that this material exhibits ferromagnetic phenomena and, if deposited on a host nonlinear single crystal, can be considered a promising magneto-optical medium. We report on nonlinear parameters of undoped and doped ZnGeP2 and current data on magnetic phenomena in (Zn,Mn)GeP2 and (Cd,Mn)GeP2 ferromagnetic layers and doped ZnGeP2:Mn single crystals. Stabilizing a heterosystem constituted by ferromagnetic layers on a nonmagnetic nonlinear crystal extends the scope of possible designs of magneto-optical, spin-dependent, and magnetically controllable nonlinear optical devices. copy 2005 Optical Society of America

Fabrication of a frequency conversion device using a novel direction controlled crystal growth method

We have developed a novel direction controlled crystal growth method which makes it possible to fabricate a phase-matched second harmonic generation (SHG) crystal from molten state. A high efficient nonlinear optical crystal, 2-adamantylamino-5-nitropyridine (AANP) was used as an SHG crystal. Glass cells with specific structure made it possible to control the AANP crystal growth direction to the phase-matched angle at 1.55 μm wavelength. X-ray diffraction measurement confirmed that the crystal was fabricated to the direction that we designed.

Growth of cadmium mercury thiocyanate single crystal for laser diode frequency doubling

Cadmium mercury thiocyanate (CdHg(SCN) 4, CMTC) crystal is one of the most efficient nonlinear optical crystals among complex crystals. Two different solvent mixtures of water–NaCl and water–KCl suitable for growing CMTC crystal are reported for the first time. A typical single crystal of CMTC with size 18×18×25 mm 3 was grown from a water–NaCl mixture solvent by using temperature-lowering method.

Calculation of nonlinear optical polarization and phase matching in biaxial crystals

We present a general, analytical formula for the calculation of the unit vectors of the direction of vibration of the electric field strength in biaxial crystals. By means of this formula it is possible to calculate the effective nonlinearity for second-order nonlinear optical frequency conversion processes in biaxial crystals. For two highly efficient nonlinear optical crystals we have calculated the effective nonlinear susceptibility and walk-off angles. The results have been compared with numerical as well as experimental data of previous papers.

Demonstration of efficient nonlinear optical crystals with vanishing molecular dipole moment: Second-harmonic generation in 3-methyl-4-nitropyridine-1-oxide

Previous research toward more efficient nonlinear optical organic crystals has aimed at increasing the first-order hyperpolarizabilitiy of individual molecular units. We show that the general features derived from these studies (high conjugation, charge transfer, and molecular asymmetry) leave room for the cancellation of the molecular dipole moment. This can be usefully exploited in two directions: improving the crystal growth conditions and a possibility of acting on the crystal point group structure through otherwise hidden parameters. Pyridine-1-oxide, owing to the electronic ’’push–pull’’ property of the N–oxide bond, allows for substitution in the 4 position of donor as well as acceptor groups, among which the nitro group ensures dipole cancellation. The possibility of charge transfer from or toward the N–oxide bond according to the nature of the radical in the 4 position is investigated and confirmed by means of second-harmonic generation experiments in powder or solution (DCFISH) on a number of compounds. 3-methyl-4-nitropyridine-1-oxide is shown to be the best candidate, among related compounds, for crystal growth. A detailed study of its linear and first-order nonlinear properties is presented. Crystalline samples grown in solution are seen to be of excellent optical quality. Its efficiency compares to that of the best available phase- matchable organic crystals [d = (23±3)×10−9 esu]. Besides, the optical broadband phase-matching potential of the crystal could be useful in a number of applications like frequency doubling of ultrashort pulses in the near infrared.