The LIAD series Radiometers use a pyroelectric or photodiode sensor in conjunction with chopped CW or quasi CW radiation, using a digitally synthesized lock-in amplifier to reduce external noise to a minimum. When connected to a compatible optical power meter, you can measure a calibrated power at a very low power level.  To maintain calibration uncertainty and guarantee performance, we recommend annual recalibration.

The signal is passed through the 18Hz chopper, included in the products, and the chopped signal is detected by the sensor. All signals not at this 18Hz frequency are suppressed. The chopper must be placed close to the signal source so as to eliminate radiation from an unwanted source.  There is a 1/4-20 hole on each side of the chopper housing, to allow a large number of mounting options.