Takafumi Uemiya

Structure and nonlinear optical properties of diacetylene thin films vapor-deposited on highly oriented polytetrafluoroethylene thin films

Five diacetylene compounds were vapor-deposited on a highly oriented thin film of polytetrafluoroethylene (PTFE) prepared by mechanical deposition. 1,6-Di-(N-carbazolyl)-2,4-hexadiyne (DCHD) film was composed of needlelike crystallites along the chain axis of the PTFE macromolecules. The DCHD crystal was oriented with respect to the PTFE crystal substrate in the relation of (100) * [010] DCHD //(100)[001] PTFE . Other diacetylenes also formed uniaxially oriented thin layers. Upon photoirradiation diacetylene films changed to polymer films having extremely high crystallinity and considerable in-plane dichroism. The third-order susceptibility X (3) of the miaxi-ally oriented polydiacetylene films were several times larger than those of the randomly oriented films. Crystal growth observed by electron microscopy on local and microscopic scales was confirmed by THG measurement on a macroscopic scale.

Modified method of electric‐field induced second‐harmonic generation

Second‐order hyperpolarizabilities β of organic nonlinear optical materials were measured by a modified method of the electric‐field induced second‐harmonic generation. Since this method avoided interference between two second‐harmonic waves from a solution and cell‐window glass, β of a dilute solution was easily determined and at the same time, a third‐order hyperpolarizability γ of a solvent was also evaluated. The obtained β values were constant in a wide range of the concentration.

Optical second-harmonic generation from a series of [cyano(alkyloxycarbonyl)methylene]-2-ylidene-1,3-dithioles and their methyl and dimethyl derivatives

Abstract Second-order nonlinear optical properties of a series of [cyano(alkyloxycarbonyl)methylene]-2-ylidene- 1,3-dithioles and their methyl and dimethyl derivatives were investigated by the powder technique. An Nd:YAG laser was used for the fundamental. [cyano(ethoxycarbonyl)methylene]-2-ylidene-4,5-dimethyl-1,3-dithiole recrystallized from methyl alcohol gave large optical second-harmonic (SH) intensity (24 times that of urea), while that recrystallized from acetone gave no SHG. [cyano(ethoxycarbonyl)methylene]-2-ylidene-4-methyl-1,3-dithiole also gave large SH intensity (10 times that of urea). These materials are almost colorless. They are attractive materials for frequency doubling of infrared semiconductor lasers in the blue wavelength region.

Frequency doubling of a Nd:YAG laser using a crystal-cored fiber of an organic 4-(N,N-dimethylamino)-3-acetamidonitrobenzene

Optical second-harmonic generation from a glass-clad fiber with an organic core crystal of 4-(N,Ndimethylamino)-3-acetamidonitrobenzene (DAN) is demonstrated. Phase matching was due to cerenkov radiation. Linear and nonlinear optical properties of DAN, a fabrication technique of a crystal-cored fiber, and a focusing method of the generated second-harmonic wave are studied.

Preparation of Large Single Crystal Thin Film of Polydiacetylene by Graphoepitaxy

The crystal growth of a diacetylene monomer was investigated by graphoepitaxy, an orientation-controlled crystal growth using a substrate with an artificial surface pattern. The direction of crystal growth was controlled by grooves prepared on a part of a fused-silica substrate surface and single crystal growth followed it on a non-grooved area next to the grooves. A large single crystal thin film with the domain size of approximately 2 x 2 mm was finally obtained. The thin film could be polymerized by UV light irradiation without any morphological change. The obtained polydiacetylene thin film was large enough to apply in an optical waveguide for nonlinear optical devices.

Crystal Cored Fiber Using Organic Material And Focusing Properties Of Generated Second-Harmonic Wave

A single crystal-cored fiber using 4-(N, N-dimethylamino)-3-acetamidonitrobenzene (DAN) was fabricated. Single mode-propagation was achieved for dense flint glass cladding. The single ring-pattern of the second-harmonic wave corresponding to the singly guided fundamental mode was obtained and its conversion efficiency was 0.42% at the fundamental power of 29.3W. After collimation using an axicon lens, the second-harmonic wave from the fiber could be focused into a smaller spot than the usual light beam with a circular aperture.

Syntheses, second-order NLO properties, and crystal structures of tetra-substituted ethylene, tri-substituted schiff-base, and diphenoxymethane derivatives

Abstract In order to obtain frequency doubler of the infrared semiconductor lasers, a series of push-pull ethylenes were synthesized. Among them, ethyl 2,2-bis(methylthio)-1-cyanoacrylate, ethyl 2-dimethylamino-2-methylthio-1-cyanoacrylate, and 2-dimethylamino-2-methylthio-1-cyanoacrylonitrile gave SHG with intensities of 5.5, 0.8, and 0.5 times, respectively, that of urea by a powder technique using an Nd: YAG laser as a fundamental wave. Their absorption edges located below 370 nm. The crystal structure analysis showed the distorted ethylene structure mainly due to the contribution of an intramolecular charge-transfer in their ground states. Their β values were calculated in an MNDO level. Diphenoxymethanes are expected to be Λ-shaped molecules and to favor columnar and non-centrosymmetric structures when packed in a crystal. Bis[ p -(2,2-dicyanovinyl)phenoxy]methane, bis[ p -(2-cyano-2-ethoxycarbonylvinyl)phenoxy]methane, and bis( p -bromophenylthio)methane gave SHG intensities 0.4, 1.4, and 0.1 times, respectively, that of urea.

Crystal Growth and Characterization of N-(5-Nitro-2-pyridyl)-(s)-phenylalaninol: A New Organic Material for Nonlinear Optics

Abstract Crystals of N-(5-nitro-2-pyridyl)-(s)-phenylalaninol having good optical quality were grown from solution. The crystal structure and the linear and nonlinear optical properties were determined. Angle tuned phase matching was achieved with a d eff = 31 pm/V and a conversion efficiency of 0.15% was obtained at the fundamental power of 50 kW/cm2 using a 0.45-mm-thick crystal.

Polymorphism and the Molecular and Crystal Structures of a Second Order Nonlinear Optical Compound Containing a 1,3-Dithiole Ring

Abstract [Cyano(ethoxycarbonyl)methylene]4,5-dimethyl-2-ylidene-1,3-dithiole, designed as an organic nonlinear optical material for the second harmonic generation (SHG), exhibits crystallographic polymorphism: the SHG inactive α-form crystallizes in the centric, triclinic space group P1 from acetone solution, while the SHG active β-form does so in the non-centric P1 from ethanol solution. In the β-crystal, all the molecular dipole moments favorably align with same orientation in layers.

Design, fabrication, and evaluation of crystal-cored fibers for efficient second-harmonic generation based on Čerenkov-radiation-type phase matching

A formulation for calculating the optical second-harmonic power based on the Cerenkov-radiation-type phase matching is derived for a crystal-cored fiber. The prerequisite condition for high efficiency is expressed by a simple relation by use of the refractive indices of a core crystal, a core radius, and a fundamental wavelength. An organic crystal-cored fiber is designed and practically fabricated by the guiding principle derived here. A blue second-harmonic wave of 1.4 mW is obtained from a 1-mm-long fiber by use of a 60-mW semiconductor laser, and the second-harmonic intensity agrees well with the prediction. Degradation of the organic core crystal caused by the generated blue wave is observed, and the lifetime of the device is evaluated.