The T.rad Series of broadband digital radiometers from Spectrum Detector Inc., Lake Oswego, OR, have sensitivity in the far IR and THz spectrum (0.1–100 THz) and are available with 1.5, 5, and 9 mm dia. probes. The pyroelectric detector and preamplifier are mounted in a metal housing that includes a thermal isolation enclosure with a threaded front bezel that takes windows, optics, and filters. A radiometer system comprises a probe and the company's LIA-DPM digital lock-in module. The radiometers can measure 50 nW with 2 nW resolution. The devices are suited for use by those developing, manufacturing, or using continuous wave IR lasers and THz sources.