Interferometric method for preventing mode-hopping in tunable external-cavity semiconductor lasers

A problem in frequency-tuning of external-cavity lasers is mode-hopping between neighbouring external-cavity modes. We demonstrate a new interferometric method for monitoring mode-hoping and an automatic control circuit for a 1.3 ?m grating external-cavity laser that maintains single-mode operation when the lasing frequency is tuned.     

Wide-span optical frequency comb generator for accurate opticalfrequency difference measurement

An optical frequency comb (OFC) generator was realized for accurate optical frequency difference measurement of 1.5 μm wavelength semiconductor lasers by using a high frequency LiNbO₃ electrooptic phase modulator which was installed in a Fabry-Perot cavity. It was confirmed that the span of the OFC was wider than 4 THz. By using semiconductor lasers whose spectrum linewidths were narrowed to 1 kHz and a sensitive optical balanced-mixer-receiver for measuring beat signal between the sideband of the comb and the laser, we demonstrated a frequency difference measurement up to 0.5 THz with a signal-to-noise ratio higher than 61 dB, and a heterodyne optical phase locking with a heterodyne frequency of 0.5 THz in which the residual phase error variance was less than 0.01 rad². The maximum measurable frequency difference, which was defined as the sideband frequency with the signal-to-noise ratio of 0 dB, was estimated to be 4 THz     

Modulation characteristic of waveguide-type optical frequency combgenerator

We report the modulation characteristics of a waveguide-type optical frequency comb generator (WG-OFCG) with the advantages of compactness, high modulation index and low driving power. The characteristics of the optical frequency comb (OFC) generated when the modulation index exceeds 2π are discussed. The power of the modulation sidebands was measured by the optical heterodyne method with an external-cavity laser as a local oscillator. The dependence of the modulation index of the WG-OFCG on the modulation frequency up to 40 GHz was measured. The generation span of the OFC at the modulation frequency detuned from an integer multiple of the free spectral range (FSR) is discussed     

Thermal response in thermal energy storage material around heat transfer tubes: effect of additives on heat transfer rates

The effects of carbon-fiber chips and carbon brushes as additives on the thermal conductivity enhancement of phase change materials (PCMs) using in latent heat thermal energy storage are investigated experimentally and numerically by considering the wall effect of the additives. The carbon-fiber chips are effective for improving the heat transfer rate in PCMs. However, the thermal resistance near the heat transfer surface is higher than that for the carbon brushes. As a result, the overall heat transfer rate for the fiber chips is lower than that for the carbon brushes. Consequently, the carbon brushes are superior to the fiber chips for the thermal conductivity enhancement under the present experimental conditions. The carbon brushes are moreover applied to the packed beds of particles to overcome their low thermal conductivity in chemical heat pump/storage. The carbon brushes essentially improve the heat transfer characteristics in the packed beds, though the thermal resistance is observed because the particles obstruct contact between the fibers and the heat transfer surfaces.     

Analysis of XANES for identification of highly dispersed transition metal oxides on supports

XANES of vanadium and niobium oxide on silica or alumina have been analyzed quantitatively by a deconvolution technique. Based on the results for reference compounds, local structures of supported vanadium and niobium species were identified. The composition was estimated from difference spectra for the samples which consisted of two kinds of species.     

Limit of optical-frequency comb generation due to materialdispersion

The limit of optical frequency comb (OFC) generation (i.e., the limit of frequency difference measurement) due to the material dispersion in the EO crystal is experimentally studied. By using a modified monolithic OFC generator, we observed the OFC spectrum, and confirmed that the envelope of the OFC around 780 nm extended to a span as wide as 16 nm (or 7.6 THz) reaching the limit of the OFC generation. We also proposed a method of stabilizing the Fabry-Perot cavity for the monolithic OFC generator     

Preparation of Aluminum Nitride Powder from Aluminum Polynuclear Complexes

AIN powder was synthesized from aluminum polynuclear complexes. Basic aluminum chloride and basic aluminum lactate were used as the aluminum polynuclear complexes. These starting materials and glucose were dissolved in water and mixed homogeneously. AIN powder was obtained by calcining after drying and precalcining at 800°C under nitrogen gas flow. Then excess carbon was removed by firing in air. Nitridation in the system was investigated and compared with that in the alumina–carbon black system. It was found that in our reaction system nitridation began and proceeded at lower calcination temperatures above 1200°C than in the alumina–carbon black system. Using aluminum polynuclear complexes, AIN was synthesized through the nitridation of γ-alumina and produced in a very fine and sharp particle size distribution.     

An Application of Silica‐Based Monolithic Membrane Emulsification Technique for Easy and Efficient Preparation of Uniformly Sized Polymer Particles

Summary: Uniformly sized polymer particles were prepared by an emulsification and polymerization technique utilizing a silica monolithic membrane, namely the “silica monolithic membrane emulsification technique”. In this paper, we utilized silica monolithic membrane as a device for the preparation of uniformly sized polymer particles. A mixture of monomers, diluents and oil‐soluble initiator was emulsified into a continuous medium through the silica monolithic membrane and polymerized. The particles obtained had a higher size uniformity than that of particles prepared by previously reported membrane emulsification techniques, such as the Shirasu Porous Glass (SPG) emulsification technique. Through the silica monolithic membrane emulsification technique, we could prepare particles having availability as a possible packing material for solid‐phase extraction (SPE) and high performance liquid chromatography (HPLC).

SEM photograph of silica particles prepared through capillary plate membrane.     

Importance of multiple-phonon interactions in molecular dissociation and nanofabrication using optical near fields

A quasi-particle (exciton-phonon polariton) model, as a simple model of an optical near-field probe, is proposed to investigate an unresolved problem in photochemical processes, i.e., why a vapor molecule can be dissociated by an incident photon with less energy than the dissociation energy only if, not a propagating far field, but an optical near field is used, and what is the mechanism leading to the photon flux dependence of the deposition rates. Incident photon energy and intensity dependences of Zn deposition rates are analyzed, and good agreement between the theoretical and experimental results is obtained. It suggests that the probe system plays an important role in vibrational transitions as well as electronic transitions in photodissociation processes, and that the couplings between the optical near field and molecular vibrations are enhanced to permit a nonresonant photodissociation inherent in the optical near field.     

Heterodyne optical phase-locked loop by confocal Fabry-Periotcavity coupled AlGaAs lasers

Two external confocal Fabry-Perot cavity-coupled 0.83-μm AlGaAs lasers phase-locked to one another by a heterodyne optical phase-locked loop are discussed. The phase error under phase-locking conditions was measured using the square root of the Allan variance. The result confirmed that the heterodyne signal was a full replica of the spectrum of the reference RF signal within the loop bandwidth. The estimated phase-error variance was 0.02 rad², i.e. ≃8.1°