Mamoru Usami

Development of a THz spectroscopic imaging system.

We have developed a real-time THz imaging system based on the two-dimensional (2D) electro-optic (EO) sampling technique. Employing the 2D EO-sampling technique, we can obtain THz images using a CCD camera at a video rate of up to 30 frames per second. A spatial resolution of 1.4 mm was achieved. This resolution was reasonably close to the theoretical limit determined by diffraction. We observed not only static objects but also moving ones. To acquire spectroscopic information, time-domain images were collected. By processing these images on a computer, we can obtain spectroscopic images. Spectroscopy for silicon wafers was demonstrated.

Terahertz wideband spectroscopic imaging based on two-dimensional electro-optic sampling technique

We extended the bandwidth of a terahertz (THz) spectroscopic imaging system based on two-dimensional electro-optic sampling. By using an optical-rectification emitter, formed by a ZnTe crystal, a high-frequency component of more than 2.0THz was detected. A calibration-free procedure with polarity inversion of the THz beam ensures us precise spectroscopy: the polarity was inverted by rotating the emitter crystal. The spatial patterns of the chemicals were extracted from the THz multispectral images in the extended spectral region.

Component spatial pattern analysis of chemicals by use of two-dimensional electro-optic terahertz imaging

We demonstrate a method of chemical mapping by using the transillumination terahertz (THz) images obtained by two-dimensional electro-optic THz imaging. The images and spectral data were measured between 0.1 and 1.0 THz. An experimental sample consisting of three chemicals was prepared, with one in two concentrations. By introducing the component spatial pattern analysis based on the least-squares method, the chemical composition, spatial distribution, and difference in concentration were clearly determined.