Scanning laser terahertz near-field imaging system.

We have proposed and developed a scanning laser terahertz (THz) near-field imaging system using a 1.56 μm femtosecond fiber laser for high spatial resolution and high-speed measurement. To obtain the two-dimensional (2D) THz images of samples, the laser pulses are scanned over a 2D THz emitter plate [DASC: 4'-dimenthylamino-N-methyl-4- stilbazolium p-chlorobenzenesulfonate] 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. Using this system, we have succeeded in obtaining THz transmission images of a triangle shaped metal sheet of millimeter-size and a human hair sample with a spatial resolution of sub-wavelength order up to ~27 μm (~λTHz/28) at an imaging speed of about 47 seconds/image for 512 x 512 pixels.