Electrooptic-based two-dimensional THz near-field imaging

Summary form only given. Since the first demonstration of THz imaging by Hu and Nuss (1995), many different approaches have been proposed to improve its spatial resolution, the data acquisition time and extend its application, such as T-ray tomography, THz near-field imaging, and real-time two-dimensional (2D) THz electro-optic imaging. Among them, the last one shows a unique advantage on the data acquisition rate, which is only limited by the CCD camera. With our newly developed dynamic subtraction technique with the frame rate as high as 70 frames per second, the signal-to-noise ratio was improved by about two orders. But the system spatial resolution of the usual 2f-2f 2D imaging system is basically limited by aberration and diffraction of the THz beam, because the electro-optic (EO) sensor is positioned at the conjugate plane of the object, which corresponds to the far-field of the THz beam. THz near-field measurement is an effective way to improve the spatial resolution of an imaging system. It is obviously not possible to realize near-field imaging in the conventional transmission EO sampling geometry because the object put right in front of the sensor will block the probe beam. Therefore we change the reflection geometry.