A calorimetric power meter is now commercially available having sensitivity and stability sufficient to measure a power level well below 1 μW. The Erickson model PM1B sensor has an input in WR10 waveguide, with a very well matched termination. The frequency response is believed to be flat throughout the submillimeter wave region. The response time of the sensor is 7 sec, but this time can be reduced through the use of thermal feedback, at the price of higher noise. An effective time constant of 1 sec is achieved with 0.15 μW rms noise, and 0.25 sec with 1 μW noise. The maximum input power is 200 mW, making the instrument useful with a wide variety of sources. The sensor head is quite small, yet well insulated from its environment.
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