A noncontact two-color pyrometer, which uses an infrared (IR) transmitting rod and IR lenses to optically measure the temperature of a molten particle as it falls in an evacuated drop tube, has been designed and tested in the laboratory and in the field. The design uses a calcium fluoride (CaF₂) rod which transports optical energy radiated from the molten particle to a beam splitter, where it is split into two signals. Each signal is filtered and focused onto an indium antimonide (InSb) photodetector which is liquid nitrogen (LN₂) cooled. A ratio of the detectors' outputs indicates the temperature of the molten particle.

In the laboratory, a blackbody calibrator is used as a source, and a shutter with a speed of 4 ms is used to simulate the particle dropping by the optical sensing port. The pyrometer has been calibrated for a particle temperature range of 650°C - 1200°C.