Extension of distance measurement range in a sinusoidal wavelength-scanning interferometer using a liquid-crystal wavelength filter with double feedback control

The optical path difference (OPD) and amplitude of a sinusoidal wavelength scanning (SWS) are controlled with a double feedback control system in an interferometer, so that a ruler marking every wavelength and a ruler with scales smaller than a wavelength are generated. These two rulers enable us to measure an OPD longer than a wavelength. A liquid-crystal Fabry-Perot interferometer (LC-FPI) is adopted as a wavelength-scanning device, and double sinusoidal phase modulation is incorporated in the SWS interferometer. Because of a high resolution of the LC-FPI, the upper limit of the measurement range can be extended to 280 microm by the use of the phase lock where the amplitude of the SWS is doubled in the feedback control. The ruler marking every wavelength is generated between 80 microm and 280 microm, and distances are measured with a high accuracy of the order of a nanometer in real time.     

Parallel two-step phase-shifting digital holography

We propose a parallel two-step phase-shifting digital holography technique capable of instantaneous measurement of three-dimensional objects, with a view toward measurement of dynamically moving objects. The technique is based on phase-shifting interferometry. The proposed technique carries out the two-step phase-shifting method at one time and can be optically implemented by using a phase-shifting array device located in the reference beam. The array device has a periodic two-step phase distribution, and its configuration is simplified compared with that required for three-step and four-step parallel phase-shifting digital holographies. Therefore the optical system of the proposed technique is more suitable for the realization of a parallel phase-shifting digital holography system. We conduct both a numerical simulation and a preliminary experiment in the proposed technique. The results of the simulation and the experiment agree well with those of sequential phase-shifting digital holography, and results are superior to those obtained by conventional digital holography using the Fresnel transform alone. Thus the effectiveness of the proposed technique is verified.     

Crystal structure of GdNi3 with superlattice alloy and its hydrogen absorption–desorption property

We synthesized the intermetallic compound GdNi₃, which has a PuNi₃-type structure (space group R-3m), and investigated its P–C isotherm. The refined lattice parameters were a = 0.4993(1) nm and c = 2.4536(4) nm. In the first absorption process, two plateaus were observed, and the maximum hydrogen capacity reached 1.07 H/M. In the first desorption process, a narrow and sloping plateau was observed at approximately 0.02 MPa. After the first full desorption, 0.6 H/M of hydrogen remained in the sample. This sample showed severe peak broadening in the XRD pattern, indicating that the metal sublattice deformed from the original alloy. No plateau region was observed in the second absorption–desorption cycle.     

Effect of substituting Si with Al and adding organic compounds on the luminescence properties of SiAlON phosphors

Abstract— Fundamental investigations on the effect of modifying the composition of nitride phosphors on their luminescence properties are required to enhance their luminescence efficiencies. In this study, the composition of nitride phosphors was modified by substituting Si with Al and adding organic compounds to investigate their effect on the luminescence of SiAlON phosphors. This approach improved the luminescence efficiency and shifted the luminescence wavelength.     

Decay characteristics of expiratory aerosol in various diffuser-induced airflow patterns using large-eddy simulation

This paper presents the decay characteristics of expiratory aerosol using large-eddy simulations coupled with Lagrangian particle tracking for evaluating the prevention of pathogen infection in a typical indoor environment. Ten cases of enclosed-rooms with five different diffuser-induced airflow patterns were investigated. For particles about 10 μm in diameter, which closely approximates the mean diameter of expiratory aerosol, the decay characteristics of each case with no obstacles proved that the most efficient case was the floor-supplied displacement type, followed by the ceiling-mounted line diffuser, floor-mounted diffuser, and ceiling-mounted square diffuser. The least effective case was the ceiling-mounted four-way cassette-type air diffuser under the same air changes per hour. However, in the situation of obstacles representing human bodies, the floor- supplied displacement type showed worse decay characteristics because of preventing the “piston flow-like” one-direction flow. On the other hand, the diffuser cases of the ceiling-mounted square type and the ceiling-mounted four-way cassette-type showed improved decay speed by exhaust and deposition. In particular, the ceiling-mounted square diffuser showed the most effective removal performance. These results imply that the flow configurations that induce small circulation caused by the inlet-outlet layout tend to improve the decay characteristics in terms of “the robust flow design” in a situation of complex flow field.