Checking The Accuracy Of A Novel Atomic Microwave Power Standard

Appeared in: Microwave & RF, July 2005, P. 54

R&D roundup:

ATOMIC STANDARDS are usually associated with frequency. But David Paulusse, Nelson Rowell and Alain Michaud with the Institute for National Measurements Standards of the National Research Council of Canada (Ottawa, Ontario, Canada) built an atomic standard  for microwave power, based on electromagnetic interaction with laser-cooled atoms. Their experiments were based on the use of laser-cooled rubidium atoms (a rubidium atomic clock normally used as a frequency standard). The atoms were dropped through a waveguide transmission line operating in fundamental mode. With this approach, the microwave field distribution is very well known and the transmitted power can be calculated using an analytical expression. The waveguide transmission line was maintained under vacuum using two reflection less windows and the transmitted power could be measured simultaneously via the cold atoms and a power sensor. The sensor/monitor was operated in CW mode and was fully compatible with common waveguide standards. The atomic power standard was compared to a power transfer standard operated in calibrated source mode (a 3-dB directional coupler and NBS-IV type power meter). The microwave power from a synthesized  source was kept constant and the field intensity time profile was set by the time of flight of the atoms through the waveguide. The power level was varied and the number of oscillations was varied each time to deduce the calibration factor. See "Accuracy of an Atomic Microwave Power Standard" IEEE Transactions on Instrumentation and Measurement, April 2005, Vol 54, No. 2 p. 692.  [on line]