A Comparison Between an Absolute Photoacoustic Power Meter and a Brewster Angle Version for Near Millimetre Waves in Free Space

The results of a comparison between absolute and non-absolute versions of a photoacoustic power meter for near millimetre waves in free space are presented. The absolute meter has been used to calibrate the non-absolute meter at 60 and 94 GHz. This allows the latter to be used as a secondary standard which can determine power levels of 2 mW with systematic errors of less than 2% and an NEP of 6μW. Hz½. The non-absolute meter is a Brewster angle version of the absolute one, and has the advantage of a responsivity which is a slowly varying function of frequency, unlike the absolute meter which has a resonant structure.