Second-order nonlinear optical properties from poled silicate channel-waveguide

Thin film waveguides of germanosilicate glass are fabricated byrf-sputtering. Second-order nonlinearity ofd ₃₃=3.2 pm/V is obtained from electrically poled film, and the lifetime of the nonlinearity is found to be310 years. The poled channel-waveguide is prepared and the Cerenkov-type phase-matched frequency doubling is successfully observed.     

Substituent effects in the mass spectral fragmentation of aryl esters

The mass spectra of m- and p-substituted phenyl acetates, phenyl propionates, phenyl chloroacetates and phenyl fluoroacetates have been determined. The fragmentation of aryl esters is affected by acyl substituents as well as by aryl substituents. Esters having acyl groups of low ionization potential show greater changes in fragmentation because of aryl substituents than those having acyl groups of high ionization potential. Each series has a fairly definite crossover point where fragmentation changes from predominant rearrangement to predominant cleavage.     

Surface electrical properties of Gd-doped PbZrO3

Work function (WF) of undoped and Gd-doped PbZrO₃ (PZG) was determined during isothermal oxidation and reduction experiments at 400 and 500 °C in the P(O₂) range between 10 and 2.1×10⁴ Pa. The obtained results are discussed in terms of two competitive effects, such as (i) an acceptor-type effect due to oxygen chemisorption and its subsequent incorporation into the oxide lattice and (ii) donor-type effect due to p(O₂)-induced structural transitions, such as decomposition of PbZrO₃ resulting in the formation of a surface layer composed of PbO and ZrO₂. Both effects have different rates of appearence and the effect on electrical potential. It was found that oxidation results in irreproducible changes of surface properties involving the formation of a low-dimensional surface layer.     

Evaluation of influence of anisotropic diffusion near a wall in near-field fluorescence correlation spectroscopy of nanoparticles

Fluorescence correlation spectroscopy (FCS) of colloidal nanoparticles using a near-field fiber probe was numerically simulated. The near-wall dynamics was simulated by accounting for the anisotropic mobility of nanoparticles owing to hydrodynamic interaction with a wall (Stokes viscous force). By comparing the simulation results with theoretical model calculations, we found that the influence of anisotropic diffusion is insignificant in near-field FCS autocorrelation analysis.     

Broad-spectrum frequency comb generation and carrier-envelope offset frequency measurement by second-harmonic generation of a mode-locked fiber laser

A frequency comb spanning more than one octave has been achieved by injecting the second-harmonic generation (780 nm) of a mode-locked fiber laser (1.56 microm) into a photonic crystal fiber. We propose and realize a novel interferometric scheme for observing the carrier-envelope offset frequency of the frequency comb. Frequency noise has been observed on the measured carrier-envelope offset frequency, which has been confirmed to be generated in the photonic crystal fiber by comparing the measured beat frequencies between cw lasers and frequency combs before and after the photonic crystal fiber. The mode-locked fiber laser is considered to be an important candidate for the light source used in realizing a compact optical frequency measurement system including applications in the telecommunication bands.     

Characteristics of ZnO epilayer on the post-annealed buffer layer on GaN/sapphire substrate by pulsed laser deposition

We employed epi-GaN substrates for ZnO film growth, and studied the deposition and post-annealing effects. ZnO films were grown by pulsed laser deposition (PLD) method. The as-grown films were annealed for one hour under atmospheric pressure air. ZnO morphologies after annealing were investigated and the post-annealed ZnO films grown at T _g =700^oC have very smooth surfaces and the rms with roughness is about 0.5 nm. Finally, ZnO post-annealed buffer layer was inserted between ZnO epilayer and GaN/sapphire substrates. It is confirmed by AFM that growth temperature of 700^oC helps the films grow in step-flow growth mode. It is observed by cathode luminescence spectrum that the ZnO film grown at 700^oC has very low visible luminescence, indicating the decrease of the deep level defects. It is also revealed by Hall measurements that carrier concentration is decreased by increasing the growth temperatures. It is suggested that low temperature buffer layer growth and post-annealing technique can be used to fabricate ZnO hetero-epitaxy.     

Absorption spectroscopy using a coherent transition radiation millimeter wave light source

The characteristics and applicability of the absorption spectroscopy system using the coherent transition radiation light source have been investigated. The configurations of the system are relatively simple. The operational conditions of an electron linear accelerator have been evaluated. The stability of the light intensity has been within ±2–3% in a wavenumber range of 4–13 cm⁻¹. The light intensity has been found to be more than six orders of magnitude higher than that for the lowest limit for detection.     

Observation of THz coherent transition radiation from single-bunch beam at KURRI-LINAC as an intense pulsed light source

A single-bunch beam has been generated using a developed high-speed avalanche-type pulser in KURRI-LINAC in order to lift restrictions of the spectral resolution in the spectroscopic study and the delay time in the time-resolved measurement. Both of the rise and fall times of the developed pulser are 110 ps. The observation of CTR has confirmed the single-bunch beam. The degree of impurity of single bunch has been estimated to be 1.5% by the analysis of the interferogram.