Etsuo Kawate

Symmetry X system and method for absolute measurements of reflectance and transmittance of specular samples

A symmetry X system that has been constructed for the absolute measurements of reflectance and transmittance of specular samples in the infrared region is described. The system has been designed so that it can be incorporated into commercial Fourier-transform infrared spectrometers. Although ten mirrors were used in this system, it is disclosed that the geometric mean of two reflectance values is independent of the reflectance difference of the individual mirrors and the optical loss at each mirror. This system achieves spectral measurements with high accuracy and within a short period of time. In particular, the system affords us the self-diagnostic ability for measured spectra, and the simultaneous measurements of reflectance and transmittance under the same geometry enable us to evaluate measurement uncertainties. Although the symmetry X system is used for infrared spectral measurements, the measurement method, design principles, and features are generally applicable to other wavelengths as well.

Submillimeter wave response of a high Tc superconducting microbridge

We observed the ac Josephson effect, the ‘‘Shapiro step,’’ at the high frequency of 584 GHz in an YBa2Cu3O7−δ grain boundary Josephson junction at 4.2 K for the first time. This Shapiro step grew to about 8% of the critical current without irradiation. We also noted that the critical current was gradually suppressed with increasing power. The critical current with irradiation was suppressed to about 97% of the critical current without irradiation. Detailed investigation revealed the consistency between the above two phenomena.

Determination of dielectric constant of a thin and low-dielectric film in the millimeter wave region

This letter presents a method for measuring free-space transmittance to study the dielectric property of a thin and low-dielectric film in the millimeter wave region. We found that multireflection keeps the height of the repeated peaks of the transmittance almost constant and that their widths quickly narrow with increase in the incident angle. We further show how the dielectric constant is set for a 20-μm-thick silicon dioxide film on a 700-μm-thick silicon substrate near the electromagnetic waves of frequency 65 GHz.

An optical accessory for absolute reflection and transmission measurements in the wavelength region from 0.24μm to 25μm

Five methods for the measurement of absolute reflectance are described and compared. Four of the methods, the V-W, V-N, integrating sphere and goniometer methods, have been in use for a number of years. The fifth is a new STAR GEM method. The acronym of STAR GEM is from the capital letters of Scatter, Transmission, and Absolute Reflection measurements using a Geminated Ellipsoid Mirror. Only the goniometer and STAR GEM methods can be used to measure reflectance and transmittance at almost any angle of incidence. The STAR GEM is used in conjunction with an FTIR (Fourier-Transform Infrared) spectrophotometer and also with a grating spectrophotometer to make reflectance and transmittance measurements in the wavelength region from 0.24&mgr;m to 25&mgr;m. Ordinate errors of the FTIR spectrophotometer are estimated from measurements in the overlapping wavelength region made by both spectrophotometers. A reflectance measurement of a non-plane surface, such as a surface of micro-ball lenses, can also be made using the STAR GEM.

Measurement method of optical scatter using a STAR GEM as a scatterometer

A STAR GEM as a scatterometer can measure diffuse reflection spectra. The acronym of STAR GEM is from the capital letters of Scatter, Transmission, and Absolute Reflection measurements using a Geminated Ellipsoid Mirror. A biconical accessory, such as the STAR GEM, has the advantage that it has very high collection efficiency and the ability to measure scattered reflected light from very small samples. However, it is generally thought of as a qualitative device. It becomes clear that the STAR GEM is superior to a goniometer on the study to measure absolute reflectance of a specular sample. Only the goniometer and its family can quantitatively measure the bidirectional reflectance distribution function (BRDF) of a sample. The purpose of this paper is to describe the possibilities and problems for the STAR GEM to measure the BRDF of a sample.

ac Josephson effect in superconducting all‐Nb thin‐film nanobridges up to 693 GHz

All‐niobium thin‐film nanobridges were fabricated with bridge sizes of 40‐nm length, 50‐nm width, and 100‐nm thickness. We investigated the performance of the nanobridges by monitoring Shapiro steps induced on the current‐voltage curves by an optically pumped far‐infrared laser. These steps have been observed up to 693 GHz (433 μm). This is a twofold increase over that previously reported on thin‐film nanobridges.

Dielectric Characteristics of PZT Films Prepared by Aerosol Deposition in Millimeter Wave Range

The dielectric properties of lead zirconate titanate [PZT, Pb(Zr0.3Ti0.7)O3] films, prepared by aerosol deposition (AD), were measured in the millimeter wave and THz range. Millimeter wave spectroscopy was applied for measurement in the frequency range from 45 to 80 GHz, and far-infrared Fourier transform measurements from 120 GHz to 20 THz was carried out. Spectroscopic data were analyzed with combination of Debye model with a distribution of Debye relaxation frequencies and harmonic oscillators. We clearly observed that the Debye relaxation took place below several tens GHz for annealed AD films. Combination of millimeter wave and THz spectroscopy was effective measurement technique for dielectric properties of ferroelectric materials at over millimeter wave range.

Comparison of AC laser calorimeter measurements with FTIR measurements of superconductors

The temperature dependence of the absorption of the thick niobium films was measured using an AC far-infrared laser calorimeter. Moreover the temperature and frequency dependences of the absolute transmission and reflection of same thin niobium nitride films were measured from 5 to 20 K and from 10 to 200 cm-1 using a fourier transform infrared spectrometer. The temperature dependencies of the skin depth and the absorptance determined independently by both methods are compared. However the skin depths and the absorptances agree well each other near and above Tc, they begin to deviate from each other with decreasing temperature below Tc.

Millimeter‐wave harmonic mixing with high Tc superconducting materials at room temperature

Harmonic generation and mixing in the 8∼80 GHz region has been studied in point‐contact junctions made with sharply tipped tungsten whisker and sintered polycrystalline YBa2Cu3O7−y or single‐crystal Bi2Sr2CaCu2Ox at room temperature. The signal‐to‐noise ratio (SNR) of beat notes as a function of harmonic number n is observed up to the tenth order and decreases with a slope of n−5.6 for even harmonic numbers. The dependence of the SNR of the beat note on a dc bias voltage and the current‐voltage characteristics have been measured simultaneously and theoretically analyzed using the current‐dependent mixing characteristics. The potential barrier and the insulating thickness for YBa2Cu3O7−y are estimated.

Scatterometer basing on a STAR GEM idea for optical measurements of microlenses

It is important to measure both reflectance (R ) and transmittance (T ) with the same accuracy. But many commercial accessories are exchanged by themselves or a sample is replaced on the other position in one accessory, when the reflection measurement is changed from the transmission measurement, so that it is impossible to measure reflectance and transmittance with the same accuracy. Accordingly the absorptance (A=1-R-T ) of the sample is not a sufficient index to evaluate the optical properties. A new scatterometer, which overcomes the defect, has been developed in AIST. It consists mainly of two ellipsoidal mirrors and a new detection system, which is composed of a hemispherical lens, a fiber optic taper and a CCD camera. These mirrors are a belt-shape and a quarter ellipsoidal mirrors with two focal points and are combined such that each focal point is a common focal point, on which the sample is placed. A rotating mirror is set on a remaining focal point of the belt-shape mirror. Each arrangement, where the rotating mirror looks at the upper or lower arm of the belt-shape mirror, is for the transmission or reflection measurement, respectively. The center of the hemispherical lens in the detection system is set on a remaining focal point of the quarter mirror, the incident plane of the fiber optic taper coincides with the image plane of the hemispherical lens and the outgoing plane of the fiber optic taper is in contact with the CCD camera. A clear image can be obtained using this detection system. The absolute values of the reflectance and transmittance and the light distributions of the reflection and transmission of the micro-ball-lenses, whose radii were 0.75, 1, 2.5 and 4.8mm, were measured. The systematic errors of our scatterometer are briefly discussed.