Scanning laser THz imaging system and its application

We have proposed and developed a scanning laser terahertz (THz) imaging system using a 1.56μm femtosecond fiber laser for high-spatial resolution and high-speed measurement. The laser pulses are scanned over a 2D THz emitter plate such as DASC(4´-dimenthylamino-N-methyl-4-stilbazolium p-chlorobenzenesulfonate), GaAs, and ZnTe crystals by a galvano meter. In this system, THz wave pulses locally generated at the laser irradiation spots transmit through the sample set on the emitter, and the amplitude of the transmitted THz wave pulse is detected by using a typical THz time-domain spectroscopy (THz-TDS) technique. We established model for distributed optical source. Using this system, we have succeeded in obtaining THz transmission image of a human hair with a spatial resolution of sub-wavelength at an imaging speed of about 47 seconds/image for 512 × 512 pixels.