Tadashi Aruga

Shift multiplexing for holographic storage system using fiber bundle referencing

We propose a shift multiplexing method for volume holographic storage using fiber bundle referencing. The reference beam is guided by a fiber bundle and multiplexing can be implemented by shifting the recording medium for a small distance. No sidelobe or period has been found and the signal-to-noise ratio is high. Multiple images are stored in a crystal with a spatial separation of 3 μm between successive holograms.

Generation of long-range nondiffracting narrow light beams.

A type of nondiffracting narrow light beam that propagates across a long range with a narrow beamwidth is presented. This beam is formed by a distorted concave spherical wave front that can be generated by a Galilean transmitting telescope with an eyepiece that has a spherical aberration. We observed an unusual image with a striped pattern in the laser beams atmospheric backscatter that provided an opportunity to examine this effect. We demonstrate the mechanism of the generation and the characteristics of the long-range nondiffracting beam. The results show that a nondiffracting core beam with a width of the order of millimeters with a propagation distance of the order of a kilometer is generated by a 10-cm-diameter laser beam.

Nondiffracting narrow light beam with small atmospheric turbulence-influenced propagation

A narrow light beam that propagates in the atmosphere with less disturbance than conventional light beams is introduced. The operating method and features of the newly proposed long-range nondiffracting beam (LRNB) are briefly demonstrated. Some experimental results of the atmospheric propagation of this beam at a distance of 500 m are shown in comparison with a conventional collimated beam and a focused beam. The results and related analyses show that the LRNB is much less influenced by atmospheric turbulence than other beams and suggest that the LRNB can apply to many fields.

Short-range verification experiment of a trial one-dimensional synthetic aperture infrared laser radar operated in the 10-µm band

A trial one-dimensional (1-D) synthetic aperture infrared laser radar (SAILR) system for imaging static objects, with two CO(2) lasers as a transmitter and a local oscillator for heterodyne detection, was constructed. It has a single receiving aperture mounted on a linearly movable stage with a length of 1 m and a position accuracy of 1 microm. In an indoor short-range experiment to confirm the fundamental functions of the system and demonstrate its unique imaging process we succeeded in obtaining 1-D synthetic aperture images of close specular point targets with theoretically expected resolution.

Incoherent-to-coherent conversion by use of the photorefractive fanning effect

A dynamic incoherent-to-coherent converter using the photorefractive fanning effect is demonstrated in a BaTiO(3):Ce crystal, and high-quality positive replicas of the incoherent image are obtained with a resolution of 32line pairs/mm. In this method the incoherent image-bearing beam modulates the transmission intensity of the coherent beam directly, and no readout beam is required. When the intensity ratio of the incoherent beam to the coherent beam is smaller than 5, the transmission intensity of the coherent beam increases almost linearly with increased intensity of the incoherent beam.

Vertical distribution of ozone: a new method of determination using satellite measurements

A new method to determine the vertical distribution of atmospheric ozone over a wide range from the spectral measurement of backscattered solar uv radiation is proposed. Equations for the diffuse reflection in an inhomogeneous atmosphere are introduced, and some theoretical approximations are discussed. An inversion equation is formulated in such a way that the change of radiance at each wavelength, caused by the minute relative increment of ozone density at each altitude, is obtained exactly. The equation is solved by an iterative procedure using the weight function obtained in this work. The results of computer simulation indicate that the ozone distribution from the mesopause to the tropopause can be determined, and that although it is impossible to suggest exactly the complicated profile with fine structure, the smoothed ozone distribution and the total content can be determined with almost the same accuracy as the accuracies of measurement and theoretical calculation of the spectral intensity.

Super high resolution for long-range imaging

A new optical system with a resolution that is superior to the resolution of the usual optical systems with diffraction limit is presented. We introduce a newly generated narrow light beam that propagates for a long range while almost maintaining its beam width and show that the beam width is narrower than that of the diffraction limit of normal optics. Thus a super high resolution is achieved for a long range, e.g., a range of a few kilometers, by the use of a 10-cm-diameter telescope. The high resolution for long-range imaging can be obtained by a Galilean telescope with a negative eyepiece that has a spherical aberration. We demonstrate theoretically high-resolution imaging by using simple objects and assuming a telescope 10 cm in diameter and a visible wavelength. A comparison of simulation results by the conventional optical system and by the special optical system clearly shows the superiority of the new system.

Feasibility study of synthetic aperture infrared laser radar techniques for imaging of static and moving objects

Techniques for two types of 10-mum band synthetic aperture infrared laser radar using a hypothetical reference point target (RPT) are presented. One is for imaging static objects with a single two-dimensional scanning aperture. Through the simple manipulation of a reference wave phase, a desired image can be obtained merely by the two-dimensional Fourier transformation of the correlator output between the intermediate frequency signals of the reference and object waves. The other, with a one-dimensional aperture array, is for moving objects that pass across the array direction without attitude change. We performed imaging by using a two-dimensional RPT correlation method. We demonstrate the capability of these methods for imaging and evaluate the necessary conditions for signal-to-noise ratio and random phase errors in signal reception through numerical simulations in terms of feasibility.

Modified shift-and-add speckle imaging algorithm.

A simple but powerful improvement of the shift-and-add method for the restoration of astronomical images is presented. In this modified algorithm, the shift vector and weight of a specklegram are estimated by computing the cross correlation between the specklegram and the current average before shifting the specklegram and updating the average. In this sense, all the information contained in the specklegrams is used for maximizing the coherence during the averaging process. Numerical simulations indicate that the suggested modification widens the applicability of the shift-and-add method to extended objects without the appearance of ghost images.

Mutually pumped phase conjugator with a rainbow configuration in BaTiO 3 :Ce crystal using nanosecond pulses

A new type of mutually pumped phase conjugator with a rainbow configuration has been demonstrated experimentally in cerium-doped barium titanate crystal that uses pulsed beams with a pulse width of 3.0 ns and a repetition rate of 40 Hz at a wavelength of 532 nm. The highest phase-conjugate reflectivity was ~24%. The dependence of the phase-conjugate reflectivity on the incident angle and distance, as well as the grating formation time for achieving 1 - e(-1) of equilibrium reflectivity, has been measured.