Experimental Evaluation of the Oxygen Microwave Absorption as a Possible Atomic Frequency Standard

Abstract

A microwave absorption line of O2 near 60 000 Mc has been experimentally investigated as a possible atomic frequency standard of high precision. Theoretical design, actual design, and results for an oxygen microwave spectrometer for use either in observing the line frequency or as a discriminator in a frequency control loop synchronizing an oscillator are described. Essential characteristics are the rate of change of spectrometer output signal with frequency and the output noise level. General expressions for these quantities for a wide range of experimental arrangements are obtained, and may be used to predict the attainable frequency precision. Characteristics in complete agreement with the theoretical values, capable of precision to less than 1 part in 109, were experimentally observed with relatively crude apparatus. These characteristics involved line widths of around 560 kc and signal/noise ratios of 83 db. Improvement by a few orders of magnitude can be confidently expected by engineering refinements. An additional result was close confirmation of the theoretical absolute intensity of the N+=7 line and a precision measurement of its frequency as (60 434.70±0.05) Mc.