PtSi Schottky-barrier (SB) FPAs have been developed for ground-based thermal imaging and spaceborne remote sensing applications, making the best possible use of its process compatibility with Si LSIs. The FPAs for mid wavelength infrared (MWIR: 3 -5 jim) thermal imaging are large format 2-D arrays with several array sizes up to 1040x1040. An original readout architecture called the Charge Sweep Device (CSD) has contributed to enhancing their sensitivities, and our stateof-the-art technology has reached a level which realizes FPAs with NETDs of the order of 30 mK. Extending the SB FPA technology to the short wavelength infrared (SWIR: 1 -3 jim) spectral region has made it possible to exploit spaceborne remote sensing applications. The space-grade performance and reliability have been demonstrated with a 4096 element and 2100 element linear FPAs.

We have developed a monolithic 512x512 element GeSi/Si heterojunction infrared focal plane array (FPA). The operation mechanism of the GeSi/Si heterojunction detector is the same as that of the PtSi/Si Schottky-barrier detector. We have fabricated the GeSi/Si heterojunction using Molecular Beam Epitaxy (MBE) technology, and have confirmed that ideal strained GeSi films are grown on Si substrates. We have evaluated the dependencies of spectral responsivity on the Ge composition, impurity concentration and GeSi thickness. and have optimized them for 8-1 2 jim infrared detection. The 512x512 element FPA has a pixel size of 34x34 jim and a fill factor of 59%. A low noise equivalent temperature difference of 0.08 K (ff2.0) was obtained with a 300 K background with a very small responsivity dispersion of 2.2 %.

Laser Raman radar offers a promising approach to the remote sensing of atmospheric pollutants in stack plume. An analysis revealed that the combination of the second harmonic of a Nd :YAG laser, a synchronous single photoelectron counting (SSPC) scheme, and narrow passband interference filter employed for light source, signal processor, and separation of Raman-scattered light respectively gave the most sensitive system for stack effluent monitoring. Using a laser Raman radar constructed on the basis of the analysis, the concentration of SO~ in the plume emitted from a 150 m high stack of a power plant was measured at a distance of 228 m.

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