THz Laser Beam Profiling by Homogeneous Photodoping of High Resistivity Silicon in a Compact Single-Pixel Detection Setup

Abstract

A compact single-pixel detection scheme for terahertz (THz) beam profiling is demonstrated. It incorporates an optical amplitude modulator that uses photodoping of a high resistivity Silicon (HR-Si) wafer with near-infrared (NIR) binary intensity masks, to modulate transmission of THz radiation through the semiconductor. A 270 nm thick indium-tin-oxide thin film deposited on glass by radio-frequency magnetron sputtering is used as dichroic mirror, such that the NIR radiation is brought at the Si wafer and the THz radiation is directed toward the detector, in a compact and efficient design. Given that homogeneous and well-defined binary masks in the form of structured intensity profiles of the NIR laser beam were needed, a beam homogenizer based on the Kohler integrator is also implemented. The profile of a THz laser beam with the wavelength of 118.8 μm was recorded using a resolution of 32 × 32 pixels and a square imaging area of 169 and 400 mm2, respectively. Also, due to the tunable nature of the laser system and symmetry of the laser cavity, more than one transverse modes of the laser cavity were imaged, namely, TEM00 and TEM01. A beam diameter of 3.25 mm in the TEM00 mode was recorded and a modulation depth of 52% at 2.5 THz was achieved with the present setup. With this paper, a THz spatial-domain imaging setup based on single-pixel method and having a compact design is proposed. Its functionality and possibility of further development are shown.