In this paper, we present an ultra-wideband microwave-modulated laser radar which is designed and fabricated for improvement of the spatial resolution both in the range direction and the azimuth direction. The amplitude modulation in a range of 0.01-18 GHz is applied to an infrared laser source of 1550 nm wavelength. The frequency and the bandwidth are assigned by the Administration of Radio under the Ministry of Internal Affairs and Communications in Japan. However, there is no bandwidth limitation in the infrared region. Considering the influence of radiation pattern for microwave antennas case, there is no side lobe in laser beam transmission. Ambiguous signal and interferences which are returned from the ground can be suppressed. A prototype of laser-radar system with a fiber collimator for both transmitting and receiving optics has been fabricated. A vector network analyzer is used to obtain S21 signal between the microwave modulation input and that of received signal. The system is, at first, applied to the measurement of the distance (position) of an object. It is proved that the spatial resolution is less than 1 cm during 5-10 m. As an initial experiment, we have succeeded to obtain 3D image of object by scanning a laser beam in two dimensions.
A 2D solution of full-wave equation is obtained considering both density and magnetic field fluctuations. X-mode polarization change mode conversion is discussed as well as possible applications to reflectometry of magnetic fusion devices.
A 7-18 GHz reflectometer system is installed to the central cell of the GAMMA 10 tandem mirror. The system is at first used to provide radial information of the density fluctuations. Two types of instabilities, low-m ExB-driven rotational modes and drift waves are identified by using the reflectometer as well as the Fraunhofer-diffraction system. The fluctuation level of both instabilities is observed to depend on the radial electric field, and is stabilized by applying a bias voltage to the end plates to suppress the ambipolar radial transport of a tandem mirror plasma.
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