Effect of Magnetic Field on Performance of SIS Mixers Measured at 385–500 GHz

We have investigated the effect of a moderately strong magnetic field (up to 1200 Gauss, 13 quantum fluxes within a single junction) on the heterodyne mixing performance of a 385-500GHz superconductor-insulator-superconductor mixer. Both experimental and numerical results indicate that the mixer conversion gain can be significantly reduced by a magnetic field. Surprisingly, the mixer noise shows very weak dependence. The overall receiver noise increase is merely caused by the intermediate frequency noise contribution amplified by a factor of gain reduction. At the expense of little system noise degradation, a relatively strong magnet field can make the mixer more stable at the bias point corresponding to its noise minimum     

Reduced Temperature Dependence of Lasing Wavelength in Membrane Buried Heterostructure DFB Lasers With Polymer Cladding Layers

An athermal operation of the lasing wavelength in a membrane buried heterostructure distributed feedback (BH-DFB) laser was demonstrated by adopting a polymer (benzocyclobutene) cladding layer which has a negative temperature coefficient of refractive index. Membrane BH-DFB lasers of core thickness 65 nm were operated under room-temperature continuous-wave conditions. The temperature dependence of the lasing wavelength was measured to be 2.45times10^-2 nm/degC, which is about 20%-30% of that for conventional semiconductor lasers     

Polarization-insensitive superluminescent diode at 1.5 μm with atensile-strained-barrier MQW

Polarization-insensitive high-power superluminescent diodes emitting at 1.5-μm were fabricated by using a tensile-strained-barrier MQW. Polarization difference as low as 5% and 3.8 mW optical power were obtained at 200 mA injection current     

Ultrafast non-linear optical properties and photoinduced relaxation dynamics of poly(2,5-thienylenevinylene)

The transient absorption spectra of a thin film of poly(2,5-thienylenevinylene) at photon energies between 1.15 and 2.55 eV are measured by femtosecond pump-probe spectroscopy, where the pump pulse (≈ 100 fs) is resonant with the π^* → π transition. Several ultrafast non-linear optical processes are observed during the temporal overlap of the pump and probe beams, including bleaching, Raman gain and induced phase modulation. The photoinduced absorbance change signals are found to shift spectrally to higher photon energies with an estimated time constant of 100–200 fs in the spectral region from 1.15 to 1.90 eV, indicating the geometrical relaxation to a self-trapped state. The transient decay curves are not described well by single exponential decays but can be fitted to a biexponential decay function. The fast and slow decay time constants are both found to increase from 0.16 to 0.86 ps and 4 to 14 ps, respectively, with higher probe photon energies from 1.44 to 1.82 eV. The fast decay component included both the relaxation of the hot self-trapped exciton to the adiabatic ground-state potential-energy surface and a phonon emission process. The slow decay component corresponds to both the decay of a thermalized self-trapped state via tunnelling to the ground state and a thermalization process. The observed spectral shift and decay kinetics are similar to photoexcitation dynamics previously observed in polydiacetylenes and polythiophenes.     

Orientation and immobilization of bacteriorhodopsin in polyacrylamide gel membranes

Summary Electric field application in the gel entrapment process by acrylamide-bisacrylamide system caused orientation of bacteriorhodopsin (in the form of purple membrane isolated from Halobacterium halobium). The observed photoelectric current upon illumination of the gel membrane was enhanced by this oriented immobilization and it was stable for considerable periods. Addition of ionic monomer resulted in further increase in the observed photocurrent and slight modifications in the photo-response behavior.This work was partly supported by a Grant-in-Aid for Special Project Research for Organic Thin Films for Information Conversion from the Ministry of Education, Science and Culture, Japan.     

Concentration of the solar radiation in a solar furnace

Energy concentration in a solar furnace is greatly influenced by the optical accuracy of the reflecting surface of the mirror. The highest density of a heat flux on the heating surface of a specimen is determined by its concentration and by the reflectivity of the mirror.

Since the apparent diameter of the moon is almost equal to that of the sun and the illumination of the moon may be adapted to the photographic determination of flux density, the rate of energy concentration in the authors' solar furnace was studied by the moon's image projected upon the heating zone in place of that of the sun.

As a result, about 300 watts per cm was obtained as the highest possible density of the heat flux in this solar furnace. This figure also agreed with the results of an optical analysis based on the practical finishing of the present mirror surface. With a heat flux of 300 watts per sq cm, in accordance with Stefan-Boltzmann's law of radiation, the highest temperature attainable is estimated to be approximately 2700°K. Besides the above, in actual experiment, approximately 2300°C was obtained in observing the melting points of binary mixtures, e.g., MgO---CoO and MgO---Cr₂O₃. Thus, the above-mentioned three approaches to the problem are in fairly good agreement.     

Automated bead alignment apparatus using a single bead capturing technique for fabrication of a miniaturized bead-based DNA probe array

We have developed an automated bead alignment apparatus for fabricating a bead-based DNA probe array inside a capillary. The apparatus uses 16 micro vacuum tweezers to extract single beads from among a large amount of beads in bead stock wells. It then manipulates single beads into the probe array capillaries. Single 100-microm-diameter beads were successfully extracted from the water-contained bead-stock well by the vacuum tweezers, which have inner and outer diameters of 50 and 150 microm. An interesting aspect is that unexpected extra beads adsorbed on the outer wall of the vacuum tweezers can be removed using the surface tension force between the water and the atmosphere. In testing the total performance of this apparatus, the DNA probe arrays with 10 sets of probe-conjugated beads and 2 plain beads were produced in the intended order in the capillaries. The time needed to align the 12 beads was 10 min, and the 16 bead arrays were fabricated simultaneously. After hybridization experiments using these fabricated DNA probe arrays, fluorescence from each bead was clearly observed.