A cw terahertz image beam is upconverted by a nonlinear optical process (e.g., sum- or difference-frequency generation with a near IR cw upconverting beam). The upconverted image is acquired by a near IR image detector. The bandwidths and center wavelengths of the terahertz image beam and the upconverting beam are such that wavelength filtering can be employed to permit an upconverted image beam to reach the detector while blocking or substantially attenuating the upconverting beam.

A MEMS infrared sensing device includes a substrate and an infrared sensing component. The infrared sensing component is provided above the substrate. The infrared sensing component includes a sensing plate and at least one supporting element. The sensing plate includes at least one infrared absorbing layer, an infrared sensing layer, a sensing electrode and a plurality of metallic elements. The sensing plate has a plurality of openings. The metallic elements respectively surround the openings. The sensing electrode is connected with the infrared sensing layer, and the metallic elements are spaced apart from one another. The supporting element connecting the sensing plate with the substrate.