Research with a cold atomic hydrogen maser

The frequency stability of the hydrogen maser is limited by thermal noise within the atomic line-width and by additive noise at the receiver. By lowering the maser's temperature its stability can be improved both through reduced thermal noise and more favorable kinetic effects in the storage process. Predicted values of the fractional frequency stability are in the range of 10 to the -17th to 10 to the -18th power for averaging intervals of 100 to 1000 seconds. The wall shift and atomic line of an oscillating maser have been measured at temperatures of 77 to 25 K. Below 50 K this was accomplished by coating the storage bulb with tetrafluoromethane (CF4) applied through the dissociator. The results of these experiments are presented and directions for future research are discussed