Absorption of terahertz radiation by a thin metal absorber in conventional and inverted bolometers

The absorption of terahertz radiation by a thin metal absorber in the bolometers of five different designs is analyzed. Main attention is paid to bolometers of three basic configurations: (i) conventional bolometers with a double-layer main optical cavity, (ii) conventional bolometers with an additional optical cavity, and (iii) inverted bolometers with an additional optical cavity. Analytical expressions that allow calculating the absorption spectra in all the considered bolometers are obtained. It is shown that conventional bolometers only with the main optical cavity made up of two dielectric layers, as well as conventional and inverted bolometers with both main and additional optical cavities, can have the absorptance close to unity in the terahertz range. At the same time, conventional terahertz bolometers are mainly selective, whereas inverted ones are broadband.