1. THz detectors over time: from thermopiles to 21st-century components

The THz range of electromagnetic waves lies between infrared and microwaves. Unlike the visible part of the electromagnetic spectrum, to which human vision is sensitive, it wasn't until advances in knowledge and electrical technology that waves beyond the infrared could be studied and used. The triggering event was Maxwell's publication in 1865 of his famous electromagnetic theory, which suggested the possibility of emitting waves with oscillating electrical circuits. This prediction was brilliantly validated in 1888 by Hertz, who emitted and detected signals of frequency ~ 50 MHz by means of a spark produced between two spheres (dipoles) under high potential difference, located at the discontinuity of a metal circle serving as an antenna. Hertz soon produced signals at 500 MHz, and Bose used the same technique in 1897 to reach the millimeter-wave range. Nichols and Tear perfected the technique...