A Broadband Micro-machined Far-Infrared Absorber

The experimental investigation of a broadband far-infrared meta-material absorber is described. The observed absorptance is $>\,0.95$ from ${\rm 1-20\,THz}$ (${\rm 300-15\,\mu m}$) over a temperature range spanning ${\rm 5-300\,K}$. The meta-material, realized from an array of tapers ${\rm \approx 100\,\mu m}$ in length, is largely insensitive to the detailed geometry of these elements and is cryogenically compatible with silicon-based micro-machined technologies. The electromagnetic response is in general agreement with a physically motivated transmission line model.