Heihachi Sato

Electro-optic variable focal-length lens using PLZT ceramic

Proposed is an electro-optic (E-O) variable focal-length lens by combining EO material with numerous transparent fine electrodes on its surface. Coating indium tin oxide transparent electrodes on a lanthanum-modified lead zirconate titanate (9/65/35) ceramic plate and introducing a parabolic index profile with dc voltage, we successfully demonstrate a positive EO variable focal-length lens, obtaining its focal length from infinity to 1 m with applied voltage up to 300 V to an electrode gap of 50 microm. Theoretical analysis is also given, together with a discussion for improving aberration and resolving power.

Efficient Second-Harmonic Generation with a Slab Waveguide Composed of Periodically Corona-Poled Organic Copolymer

Using the slab waveguide composed of spin-coated vinylidene cyanide/vinyl acetate (VDCN/VAc) organic copolymer having the square-shaped corrugation of nonlinear optical susceptibility χ(2) with corona discharge in the guiding layer, and taking quasi-phase matching between the dominant modes of both fundamental and second-harmonic waves, enhancement of second-harmonic generation (SHG) has been demonstrated at Nd:YAG 1.06 µm and Er:YAG 2.94 µm laser lines. The SHG power with this χ(2) corrugated slab guide is theoretically evaluated, together with its enhancement factor (E.F.) to a bulk scheme. The E.F. of 500 to 800 obtained in the experiments is consistent with the theoretical estimates.

Temperature dependence of the Faraday effect in As–S glass fiber

Temperature dependence of the Faraday effect is investigated for As2S3 fiber at 3.39 microm, obtaining a Verdet constant V of 1.62 x 10(-2) min/cm x G at room temperature and a temperature-dependence term coefficient of 10.67 min x K/cm x G in the experiments. The V value obtained at 25 degrees C is consistent with the theoretical estimates based on the first derivative of known refractive indices with respect to the wavelength. The temperature-dependent term is also discussed theoretically.

Enhanced second-harmonic generation with Cerenkov radiation scheme in organic film slab-guide at IR lines

Second-harmonic generation is enhanced with both symmetric and asymmetric slab-guides composed of vinylidene cyanide/vinyl acetate copolymer film and a fused silica in the Cerenkov radiation scheme at Nd:YAG 1.06 mu m and Er:YAG 2.94 mu m laser lines. At 1.06 mu m wavelength an enhancement factor of about five in comparison with a bulk scheme has been obtained with the symmetrical Cerenkovian configuration having the film thickness d approximately=5 mu m. Extending the theory to the experimental model presented, the results are well explained theoretically, and an enhancement of the SHG power by a factor of 50 can be expected if d approximately=0.5 mu m. >

Dual focal point electro-optic lens with a Fresnel-zone plate on a PLZT ceramic

A new dual focal point electro-optic lens that is switchable to focusing and unfocusing is proposed and successfully demonstrated. This electro-optic lens is constructed by coating transparent fine electrodes in the Fresnel-zone plate onto a PLZT ceramic plate. Its focal length changes from 1.25 m to infinity binary at 515 nm with the external voltage of 210 V.

Improvement of the Cerenkov Radiative Second Harmonic Generation in the Slab Waveguide with a Periodic Nonlinear Optical Susceptibility

Introducing a periodically corrugated nonlinear optical (NLO) susceptibility χ(2) in the guiding layer of a three-layered slab waveguide, we propose a Cerenkov radiative second harmonic generation (SHG) with numerical calculations, and experimentally demonstrate it. With vinylidene cyanide/vinyl acetate copolymer film having a sinusoidal χ(2) corrugation of 60 µm period as a guiding layer, the Cerenkov scheme of SHG was enhanced over a wide film thickness range at 1.06-µm fundamental wavelength, obtaining an enhancement factor of ~1.5 in comparison with a uniform χ(2) scheme. Experimental dependences of the SHG power on both corrugation period and path length agree well with theoretical estimates, indicating usefulness of the modified Cerenkovian SHG with the corrugated χ(2).

Effect of Gas-Flow Velocity on Transient Behavior of Gain Constant in a Fast-Axial Flow Type CO2 Laser Amplifier

Depending on the gas-flow velocity v together with the discharge current Idis, the decrease of an output power amplified through a fast-axial flow type (FAF) CO2 laser amplifier has been observed within a few minutes after discharging its plasma tubes. Taking into account the effects of v and/or Idis on the gas temperature, the pumping rate to the upper laser level and the dissociation of a CO2 molecule, the gain constant is formulated as a function of discharge time for a partially homogeneously broadened laser medium at individual vibrational-rotational transitions, under the conditions of the small-signal approximation and the resonant amplification. The experimentally determined small-signal gain is compared with the theoretical estimate based on the above formulation, being in good agreement with each other. Resultantly, the dependences of the observed power decrease and transient time to have a stable output power upon v with Idis are also compared with the calculations and found to be consistent.

Second-harmonic generation in amorphous vinylidene cyanide/vinyl acetate copolymer using a pulsed Nd:YAG laser

Second-harmonic generation was recently observed in an amorphous vinylidene cyanide/vinyl acetate copolymer film by using a pulsed Nd:YAG 1.06-microm laser.

A new electrically controllable diffraction grating using polarization reflection

An electrically controllable diffraction (ECD) grating using a polarization reflection from an electro‐optic (EO) material is proposed and investigated in the experiments. The fundamental characteristics of this ECD grating are given experimentally for a He‐Ne 0.63‐μm laser. The grating used consists of a PLZT ceramic with ten pairs of interdigital electrodes having a period of 400 μm. Applying the electric field to the electrodes, the diffraction pattern can be changed due to the deviation of the reflectance of the EO material. Near the zeroth‐order diffraction peak the maximum modulation degree of 33% was obtained with an applied peak voltage of 100 V at an incident angle 60°.

Enhanced SHG power using periodic poling of and vinylidene cyanide/vinyl acetate copolymer

Embedding poling-inverted corrugation of the optical nonlinear susceptibility into vinylidene cyanide/vinyl acetate organic copolymer, the second-harmonic (SH) power has been enhanced at pulsed Nd:YAG 1.06 /spl mu/m and Er:YAG 2.94 /spl mu/m laser lines by quasi-phase matching (QPM) the interaction between the fundamental and SH waves. Using a sample with a corrugation period of 120 /spl mu/m with poling corrugated by an interdigital electrode, an enhancement factor of about 94 and /spl sim/3 was obtained at 1.06 /spl mu/m and 2.94 /spl mu/m, respectively, in comparison with a bulk sample having uniform poling. Taking the first-order QPM, the maximum conversion efficiency was also about 0.001 percent at the wavelength /spl lambda//sub /spl omega//=1.06 /spl mu/m, with the fundamental peak power P/sub /spl omega// of 2.5 W, and the extinction coefficients of /spl alpha//sub /spl omega//=/spl alpha//sub 2/spl omega//=0.7 mm/sup -1/ in the film having a path length of 2.4 mm, while /spl sim/0.03 percent at /spl lambda//sub /spl omega//=2.94 /spl mu/m with P/sub /spl omega//=200 W, and /spl alpha//sub /spl omega//=1.4 mm/sup -1/ and /spl alpha//sub 2/spl omega//=0.7 mm/sup -1/ for the same film. >