Atsushi Minato

Optical design of cube-corner retroreflectors having curved mirror surfaces

The characteristics of retroreflectors that include curved mirror surfaces are theoretically investigated. The use of curved mirror surfaces in a cube-corner retroreflector is an effective method for diverging the reflected beam, especially in a large-aperture hollow retroreflector. The effect of curved surfaces is demonstrated for simple examples that give circular and elliptical wave-front patterns. The method was applied in the optical design of a satellite retroreflector in space, which is to be loaded on the Japanese polar orbit Advanced Earth Observing Satellite.

Long-path absorption measurement of CO 2 with a Raman-shifted tunable dye laser

A laser long-path absorption system was developed with a hydrogen Raman shifter pumped by a tunable dye laser. The absorption spectrum of CO(2) in the 2-µm region was measured in the open air with a retroreflector or a hard target. The concentration of CO(2) was determined from the spectrum by the least-squares method. Noise in the system was analyzed, and the propagation of error to the obtained concentration was investigated. The statistical error in the concentration was estimated at approximately 1% for a single spectrum measurement. Comparison with the simultaneous measurements with a nondispersive infrared gas analyzer showed good agreement.

Design of a four-element, hollow-cube corner retroreflector for satellites by use of a genetic algorithm

A four-element retroreflector was designed for satellite laser ranging and Earth-satellite-Earth laser long-path absorption measurement of the atmosphere. The retroreflector consists of four symmetrically located corner retroreflectors. Each retroreflector element has curved mirrors and tuned dihedral angles to correct velocity aberrations. A genetic algorithm was employed to optimize dihedral angles of each element and the directions of the four elements. The optimized four-element retroreflector has high reflectance with a reasonably broad angular coverage. It is also shown that the genetic algorithm is effective for optimizing optics with many parameters.

Optical design of a hollow cube-corner retroreflector for a geosynchronous satellite

The optical characteristics of a single-element hollow cube-corner retroreflector for a geosynchronous satellite were numerically evaluated for laser ranging and laser long-path absorption measurements of atmospheric species. An optical design with spherical surfaces and tuned dihedral angles was considered to compensate for velocity aberrations. The parameters for the retroreflector were optimized with genetic algorithms for different retroreflector sizes and wavelengths (500 nm and 1, 3, and 10 microm). We found that 20-cm retroreflectors are sufficient for realistic measurements when the laser wavelength is 500 nm or 1 microm. However, a larger retroreflector is necessary to overcome the detector noise level at 3 and 10 microm.

Improved limb atmospheric spectrometer and retroreflector in-space for ADEOS

The ILAS and RIS instruments for Advanced Earth Observing Satellite intended to perform laser absorption measurements are described. The ILAS measurements will provide vertical profiles of ozone and ozone-related species in the polar regions. The RIS will obtain vertical profiles of ozone, carbon dioxide and methane as well as column density of some greenhouse gases based on laser absorption measurements.

RETROREFLECTOR WITH ACUTE DIHEDRAL ANGLES

An acute-angle retroreflector having three dihedral angles of 45, 60, and 90 deg was studied by use of the ray-trace method. Incident rays are reflected nine times in the retroreflector, and there are 26 different sequences for reflections. Errors in the dihedral angles will cause the directions of the reflected rays to diverge. A possible application of the acute-angle retroreflector is in target design for laser ranging.

Method for measuring dihedral angles of a cube-corner retroreflector having curved mirror surfaces

Measurement of dihedral angles of a cube-corner retroreflector with curved surfaces is discussed. A simple method for measuring a dihedral angle from an interferogram is given based on theoretical consideration. A general method to obtain three dihedral angles by means of least-squares fitting of the interference fringes is also described. The method is tested by means of simulation data.