Tatsuo Nozokido

Scanning near-field millimeter-wave microscopy using a metal slit as a scanning probe

In this paper, a novel type of scanning near-field millimeter-wave microscopy using a metal slit-type probe is proposed. A tapered reduced-height rectangular waveguide forms the slit aperture, which has a width much smaller than one wavelength /spl lambda/ and length of the order of /spl lambda/. The slit probe can be operated in the TE/sub 10/ mode and, thus, results in high transmission efficiency, even when the width is exceedingly small. An image reconstruction algorithm based on computerized tomographic imaging is used to obtain two-dimensional near-field images. Experiments performed at 60 GHz (/spl lambda/=5 mm) show that image resolution equal to the slit width (/spl sim/80 /spl mu/m) is achieved. As an application of this scanning slit microscopy, visualization of transition phenomena of photoexcited free carriers in silicon have been successfully demonstrated, yielding useful information on the dynamics of free carriers in semiconductor materials.

Refractive index of nematic liquid crystals in the submillimeter wave region

Large electro-optic effects of liquid-crystal materials are attractive in applications to various optical devices in a wider wavelength region. Fundamental optical properties in the submillimeter wave region, such as refractive indices and transmission losses for some cyanobiphenyl nematic liquid crystals, have been investigated for the first time, to our knowledge, with a submillimeter laser. Refractive indices of the liquid crystal materials for ordinary and extraordinary rays are a little larger than those in the visible region, and a larger birefringence comparable with the visible region can also be obtained. Although the loss level is larger by ~2 orders of magnitude than that of quartz plate, which is an excellent window in the submillimeter wave region, the transmission of the liquid crystal cell is high enough.

Isotropic photonic gaps in a circular photonic crystal

We investigated the optical properties of a circular photonic crystal (CPC) for which the distance between lattices was systematically distributed. The transmission spectra of CPC composed of alumina cylinders were examined in the frequency region from 0 to 20 GHz. We show that photonic gaps are obtained not only in CPCs but also in phase-shifted CPCs. The isotropic photonic gaps are evidenced by changes in the incident angle of a millimeter wave.

High-transmission waveguide with a small radius of curvature at a bend fabricated by use of a circular photonic crystal

A bent photonic crystal waveguide was fabricated by use of a lattice pattern of a circular photonic crystal that allowed high transmission for a broad band of wavelengths with a small radius of curvature at a bend. The waveguide was fabricated by use of alumina rods with a diameter of 3 mm. Windows of high transmission as a result of waveguiding were observed near 9 and 15 GHz. By measurement of the relative wave intensity [E]2 along the line defects, the propagation losses in the straight and the bent sections were estimated at 9.3 GHz to be 0.04 and 0.03 dB/mm, respectively.

Millimeter-wave scanning near-field anisotropy microscopy

A millimeter-wave scanning near-field microscopy using a slit-type probe, which permits the observation of electrical anisotropy in the viewed object, is proposed. The slit probe is sensitive to any electrical anisotropy along the object surface direction that is inherent in the object to be imaged, because the electric field at its aperture is linearly polarized. An electrical anisotropy model is incorporated into the image reconstruction process that enables two-dimensional image reconstruction. The details of the model and the reconstruction method adopted in this work are described and experimental results to demonstrate the feasibility of this microscopy format are presented.

Experimental verification of the theory on the inverse Smith–Purcell effect at a submillimeter wavelength

The inverse Smith–Purcell effect is a candidate for laser‐driven linacs utilizing the interaction between laser light and an electron beam traveling just in front of a metallic grating. We have performed experiments to study electron energy spread as a function of electron beam position above the grating. A submillimeter wave laser (CH3F, 496 μm) is used as a driving source. It is found that the energy spread characteristics show exponential decay of the interaction strength (field intensity) in the direction perpendicular to the grating surface, as a classical theory on the effect predicts.

High peak power and high repetition rate characteristics in a current-pulsed Q-switched CO/sub 2/ laser with a mechanical shutter

An electro-mechanical Q-switched (EMQ) CO/sub 2/ laser is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current. Such a system can produce pulses with high peak powers (>10 kW) and high repetition rates (>1 kpps). In order to analyze the output characteristics, the peak power and the duration of the output pulses have been measured experimentally in detail over a wide range of Q-switching times up to 250 ns. For a low-pressure ( >

Determination of the Insertion Loss and Refractive Index Anisotropy in Nematic Liquid Crystal Materials Using a V-band Waveguide Transmission Cell

Large electrooptic effects based on the reorientation of liquid crystal molecules are expected in the high frequency electromagnetic wave region. However, there is only limited information about the optical and/or dielectric properties of the liquid crystal (LC) materials except for the visible and very low frequency region. Here, we try to determine the loss parameter and refractive index anisotropy of the commercially available nematic liquid crystal materials in the millimeter wave (MMW) region by using a V-band (50 GHz – 75 GHz) rectangular waveguide test cell. Loss parameters are determined by fitting the theoretical data based on the multiple reflection phenomena to the measured transmission spectra. Refractive index anisotropy is derived from the phase difference between the horizontal and the vertical LC molecular orientation states. It is found that the usual nematic LC materials are transparent in the millimeter wave region and the refractive index anisotropy is still large.

Difference spectra measurement of squid rhodopsin in the submillimeter wave region

Theoretical studies by computer simulation have shown that vibrational modes, which depend on the subdomain motions of proteins, are located in the submillimeter wave region (i.e., 10-100 cm(-1)], 0.3-3 THz). We have successfully observed, by measuring the difference spectrum between squid rhodopsin and metarhodopsin to avoid water absorption, that squid rhodopsin shows its absorption features in this region. Our experimental results show that a native protein in solution indicates not only an absorbent property in this region but also an actual change of absorption with changes in protein conformation.

Measurements of the inverse Smith-Purcell effect at submillimeter wavelengths

The inverse Smith-Purcell effect was observed to verify the theoretical predictions for the dependence of the size of the interaction space on the laser wavelength. Two submillimeter wave lasers with wavelengths of 184.6 mu m and 496 mu m were used as the driving lasers. It was found that the interaction strength for the driving laser with shorter wavelength decays more rapidly than that for the longer wavelength driving laser, as is predicted by theory. Measured decay constants of the field intensity have shown good agreement with theoretical values.<<ETX>>