Toward user-friendly thermal radiometers; Microfabrication of novel photo-thermal sensors and broadband ultra-black absorbers

Amemiya, Kuniaki*; Koshikawa, Hiroshi; Yamaki, Tetsuya; Maekawa, Yasunari; Shitomi, Hiroshi*; Kinoshita, Kenichi*; Numata, Takayuki*; Tanabe, Minoru*; Fukuda, Daiji*

A thermal radiometer absorbs all incoming photons and has a high sensitivity to detect the resulting temperature rise. The big challenges here were insufficient mechanical stability of broadband ultra-black absorbers and low sensitivity of photo-thermal sensors. We developed a robust optical absorber and low-noise photo-thermal sensor by new microfabrication techniques. The optical absorbers had micrometer-sized surface structures of chemically-etched ion tracks on CR-39 plastic and hard carbon coating as an optical absorption layer, therefore, exhibiting a spectral reflectance suppressed to below 1% in the ultra-violet to near infrared range of wavelengths. Importantly, they were never made susceptible to dust blow off as well as to mechanical contact. The photo-thermal detectors were equipped with the bimetal MEMS system, which can sensitively respond to thermally-induced deformation. They were found sensitive enough to reach almost the theoretical limit.