Highly efficient single-photon detection at communication wavelengths by use of upconversion in reverse-proton-exchanged periodically poled LiNbO3 waveguides

Conventional single-photon detectors at communication wavelengths suffer from low quantum efficiencies and large dark counts. We present a single-photon detection system, operating at communication wavelengths, based on guided-wave frequency upconversion in a nonlinear crystal with an overall system detection efficiency (upconversion + detection) exceeding 46% at 1.56 microm. This system consists of a fiber-pigtailed reverse-proton-exchanged periodically poled LiNbO3 waveguide device in conjunction with a silicon-based single-photon counting module.     

Complexation and chiral recognition thermodynamics of gamma-cyclodextrin with N-acetyl- and N-carbobenzyloxy-dipeptides possessing two aromatic rings

The stability constants (K) and the standard free energy (deltaG degrees ), enthalpy (deltaH degrees ), and entropy changes (deltaS degrees ) for the complexation of gamma-cyclodextrin with 34 enantiomeric and diastereomeric N-acetyl- and N-carbobenzyloxy-d/l-dipeptides with two aromatic moieties were determined in aqueous buffer solution at 298.15 K by titration microcalorimetry. Chiral recognition of the enantiomeric dipeptide pairs by gamma-cyclodextrin was found to be fairly poor, exhibiting only small percentage differences in K, while the diastereomeric dipeptides were discriminated to much greater extent with affinity differences of up to 6-7 times. The complex structures of several selected pairs were elucidated by NMR techniques. Combining the microcalorimetric and NMR data, the complexation and chiral recognition behavior of gamma-cyclodextrin is discussed in particular in terms of the length, bulkiness, and flexibility of the tether connecting the two aromatic moieties in a guest.     

Complete stereochemistry of tetrafibricin

With use of the NMR databases in achiral and chiral solvents, the complete stereochemistry of tetrafibricin (1) has been elucidated without degradation of the carbon framework. [structure--see text]     

Solid state ion trap: Lateral confinement of quantum well excitons by oscillating piezoelectric field

We theoretically investigate a new type of lateral trap that can be used to confine quantum well excitons. By sending an ultrahigh frequency bulk acoustic wave from the substrate of III-V semiconductors such as GaAs or GaN, an oscillating piezoelectric field is generated. The effective potential induced by the oscillating piezoelectric field implements a type I lateral trap. Such a controllable quantum confinement is essential in many semiconductor nano-electronics and nano-photonics applications.     

Optical Super-Resolution Pickup Using a Liquid Crystal Shutter for CAD-MSR Magnetooptical Disk

We demonstrated characteristics of an optical super-resolution pickup using a liquid crystal (LC) shutter as a shading plate. The problem of laser power loss was solved by an LC shutter which was turned off for writing and turned on for reading. Combining this with CAD-MSR disk, we obtained good signals of high-density recording. This combination increases efficiency of laser power and does not require a slit to eliminate side-lobes. The laser power efficiency for writing is as high as 34% and linear bit density reaches 0.255 μm/bit even with a wavelength of 680 nm and an objective lens NA of 0.60.     

Fiber-Optic Ammonia Sensors Utilizing Rectangular-Cladding Eccentric-Core Fiber

A new fiber-optic ammonia sensor utilizing rectangular-cladding eccentric-core fiber and a sensitive film containing an indicator dye is demonstrated. The sensitive film is a SiO₂-GeO₂ gel film including an indicator dye of bromocresol purple or bromocresol green, which is dip-coated by a sol-gel technique. The attenuation of this sensor changes depending on the concentration of ammonia at the wavelength range of 500–700 nm. This sensor can detect several ppm of gaseous ammonia. Various factors determining the sensitivity to detect the ammonia gas and time response of the sensor are also studied.     

New Generation of Phase-Doppler Instruments for particle velocity,size and concentration measurements

Phase-Doppler anemometry (PDA) is applied for particle size, velocity and concentration measurements in two-phase or multi-phase flows of ever increasing complexity. For accurate measurements the experimenter must be provided with software and hardware which permit an optimal layout of the PDA optics for a given application, reliable detection of signals over a wide particle diameter range, accurate determination of particle concentration and precise discrimination between particles of different composition. Recent work at LSTM, Erlangen, has been directed to developing a complete PDA package for the above purposes. Progress in this direction is summarized in this paper.