椎名 達雄

In this study, we aim to develop a mini-lidar system using a LED (Light Emitting Diode) as the light source for near-range measurement. Because LED is small size device and its wavelength is selectable, the LED lidar can be specialized in near-range measurements. In this prototype of the LED mini-lidar, the pulse power is more than 100 mW. And the pulse repetition rate and the pulse width were 112kHz and 10.2ns, respectively. The LED lidar system realized a coaxial optical system by a mirror with a hole. From hard target measurements, we verified receiving characteristics of the LED lidar according to the inversely square of distance from 0 to 100m. We also obtained lidar echoes of the atmosphere in the near range of 50m. © 2011 IEEE.

There are large demands to monitor the atmosphere in the closed space (hall, factory and so on), to check vegetation remotely and to detect hazardous gases such as explosive gas and bio terror from explosion-proof distance. On the contrary, traditional lidars have blind area, it is hard to monitor the atmosphere and the gas in the near range. In this study, optical designs and concrete developments for the atmosphere monitoring and the certain gas detection in near range were accomplished. Unique optical designs are introduced and their practical setups are explained.

The rotation of polarization plane of a propagating beam caused by a high voltage discharge was experimentally examined. Using a CW visible laser and repeating mirror optics, the rotation angle of &lt 1 deg was measured with a differential detection of &lt 30 dB. The waveform of the rotation angle showed good correlation with the discharge current waveform, with a correlation coefficient of &gt 0.94.

We examined the measurement precision of low-altitude atmospheric echo obtained by a high-precision polarization lidar Estimation of extinction coefficient of the atmosphere and low-altitude cloud dynamics were also considered

The polarization angle rotation of the propagating beam was estimated in a partially ionized atmosphere under discharge conditions. The polarization plane angle rotation is caused by the magneto-optical effect (Faraday effect). The estimated rotation angle is of the order of < 1 degree, but can be detected with an extinction ratio of polarization of > 30 dB. We examined the effects of the optical path length of repeating square mirror optics and an air-gap length of the discharge on the rotation angle. (c) 2008 Wiley Periodicals, Inc.

The rotation angle of polarization plane of propagating beam was experimentally measured using a polarization controlled laser beam, repeating square mirror, and discharge apparatus. A rotation angle of 0.29 degrees was obtained in the case of discharge gap of 4 cm and charge voltage of 50 kV. The result was in good agreement with the simulation of the experimental model. The waveform of the rotation angle showed a similar time dependence as the discharge current, with a correlation coefficient of &gt 0.94. © 2008 The Institute of Electrical Engineers of Japan.

Long-range propagation characteristics of an annular beam were examined from the viewpoint of lidar application. The annular beam permits to use a reflecting telescope for transmission and improves the transmission efficiency because it can pass through the telescope without the obstruction of the telescope's secondary mirror. As the annular beam can enlarge up to the telescope diameter, it can be eye-safe and its divergence is also reduced. The annular beam generated by a couple of Axicon prisms; conical prisms, transforms its beam shape into the central peak narrow beam; nearly non-diffractive beam, through the far-field propagation. We evaluated how the central peak intensity and its width of the transformed beam change in long-range of 3-100 km. The difficulty of the optical arraignment and the requirement of the beam quality to obtain the enough performance of the beam shape transformation were also examined theoretically and experimentally for the lidar application. The stability of the transformed beam was also confirmed in the atmospheric fluctuation. (C) 2007 Elsevier B.V. All rights reserved.

The polarization angle rotation of the propagating beam was estimated in a partially ionized atmosphere under discharge conditions. The polarization plane angle rotation is caused by the magneto-optical effect Faraday effect. The estimated rotation angle is of the order of &lt 1 degree, but can be detected with an extinction ratio of polarization of &gt 30dB. We examined the effects of the optical path length of repeating square mirror optics and an air-gap length of the discharge on the rotation angle.

This study examines the feasibility of optical remote measurement of the electromagnetic field or the electron density distribution in thundercloud. We considered the contribution of Faraday effect as the magneto-optical effect to the change in polarization of the backscattered light, assuming a polarizing lidar configuration. We estimate that, if the lidar can detect the polarizing rotation angle in the plane perpendicular to the propagating beam with a dynamic range of more than 30dB, the lidar can be used to predict lightning strikes.

An in-line type compact micropulse lidar (MPL) with an annular beam was developed for low-altitude cloud measurement. An optical circulator and a couple of axicon prisms for an annular beam were installed on the lidar optics. The advantage of using the in-line MPL is its ability to obtain a near-range measurement with a narrow field of view of 0.1 mrad and to obtain a depolarization measurement of the orthogonally polarized echoes caused by ice crystals of a low-altitude cloud. The total insertion loss of the lidar optics was 3 dB. Detectors such as avalance photodiode detectors can be operated in an analog mode near the breakdown voltage because of the high isolation of the optical circulator. The ideal lidar echo variation from the nearest distance was verified by measuring the mountain echoes at various distances. The depolarization measurement of a low-altitude ice cloud was also demonstrated. © 2005 Optical Society of America.

An in-line type micropulse lidar (MPL) with an annular beam was designed and the transmitting and receiving characteristics were analyzed. Because the in-line MPL utilizes a common telescope for a transmitter and a receiver and the annular beam always overlaps with the receiver's field of view (FOV), it can measure near-range lidar echoes with a narrow FOV. The transmitting annular beam changes its shape to a nearly nondiffractive beam through propagation. It improves the spatial resolution of the lidar observation. The receiving characteristics showed the ideal lidar echo variation, which was inversely proportional to the square of the distance the beam propagated, even if it was in the near range. © 2005 Optical Society of America.

We have developed a novel temperature measurement system for controlling the temperature of each layer of multilayered substrates, such as a silicon on insulator (SOI), and have evaluated the system using a three-layered substrate, whose top and bottom layers are silicon, each 360 mum in thickness, and whose interlayer is quartz, 1 mm in thickness. From these results, we have confirmed that the system has a resolution of less than 1degreesC in the top and bottom layers of the substrate.

A new scanning mechanism for changing long optical paths is proposed. This mechanism consists of corner reflectors arranged equally upon a disk and an outer mirror. Rotating the 120-mm? disk cases a long-optical-path change in each reflector with a near linearity of more than 40 mm. An optical coherence tomography system is described that confirms the usefulness of the proposed mechanism. Its operating characteristics and accuracy are evaluated by analysis and experiment. The deviation of the optical-path change is less than 1.52% at a reflector rotation angle of ±10°. A high-speed lock-in amplifier is utilized for fundamental measurements of glass samples. ? 2003 Optical Society of America.

A new scanning mechanism for a long optical path change in an interferometer is proposed. It consists of corner reflectors, arranged on a rotating disk at regular intervals, and an outer mirror. A reference beam in the interferometer is reflected on the corner reflector and the mirror, and then comes back to the same way whenever the reflector moves along to the disk rotation. This action makes it possible to obtain a long path change with nearly linear motion. An optical path length change, a scanning speed, and a repetition rate can be designed suitably. The rotating disk of the diameter 120mm gives the optical path change of more than 40mm. The deviation of the optical path change against the linear motion is less than 0.3%. An optical coherence tomography system with the proposed long path optical scanner has been developed and evaluated the motion characteristics. With the disk size mentioned above, the maximum repetition rate was designed as 15scans/s at the disk rotation of 60rpm. We have demonstrated the fundamental experiment of samples such as stacked slide glasses and a mirror separated from a slide glass. The experiment was in good agreement with the prediction.

The application of an optical circulator is demonstrated for an in-line-type lidar. The lidar’s transmitter and receiver are installed in a telescope. The optical circulator of interest here can separate the transmitting laser beam and the echo lights on the same optical axis. It can also divide the echo lights simultaneously into orthogonally polarized components. An insertion loss of 2.2 dB and isolation of &gt 60 dB for the developed optical circulator are obtained in a laser-transmitting situation. This optical circulator makes it possible to measure the polarization ratio caused by cloud phases with a narrow field of view in an in-line-type lidar operation. © 2002 Optical Society of America.

We have investigated characteristics of a commercially available one-chip white-LED based on indium-doped gallium nitride when modulating with an electrical pulse. The observation of a spectrum of the white-LED revealed that it contained four large peaks at wavelengths of 390nm (ultra-violet), 430nm (blue), 510nm (green), and 620nm (red), respectively. When the LED was modulated by use of a squared pulse signal with a 16kHz repetition frequency and an 85% duty cycle, each color exhibited different electric characteristics: ultra-violet and blue colors showed the similar electrical spectrum of the original input signal having three frequency bands (1st band: 16similar to108kHz, 2nd band: 108similar to208kHz, 3rd band: 208-320kHz), meanwhile a green color was presented in the two bands and a red component did not manifested in any bands. The measured result can be explained in terms of different response of the fluorescent materials responsible for the light emission. Use of electrical band filters enables to separate a white light into desired one.

ZnSe and InGaN based white-LEDs have been utilized for an interferometer. These white-LED consist of blue-LED light and yellowish green one. When these white-LED were modulated by rectangular wave, there were differences in response speed between blue-LED light and yellowish light. The response speed of blue-LED light of ZnSe type white-LED was 50ns, while that of yellowish light was 5mus. The spectral bandwidths of the blue-LED light and the yellowish light were 10nm and 100nm, respectively. Coherence lengths of these lights were 10mum and 2mum, respectively. Combining the blue-LED light with the yellowish light, we observe an unique interference when scanning the optical path of the low coherence interferometer. We also propose a method for a color separation of an interference in a low coherence interferometer with the ZnSe white-LED modulation. The ZnSe white-LED was modulated with much higher frequency (100kHz) than the Doppler frequency of the above interference. The interference fringe of white light appeared at the upper. side on the rectangular modulated light emission, while that of the residual yellowish light was presented at the bottom. The interference fringe of the blue light was derived by subtracting the yellowish light interference from the white light one.