Cryogenic hydrogen maser

A new type of atomic hydrogen maser that operates in a dilution refrigerator has been developed. In this device, the hydrogen atoms circulate back and forth between a microwave pumped state invertor in high field and the maser cavity in zero field. A prototype maser with a small maser cavity has been built and the results obtained so far are encouraging. Stable maser oscillations were observed for temperatures of the maser bulb between 230 mK and 660 mK and for densities up to 3 x 1012cm⁻³. The short term frequency stability was measured with the help of two high quality quartz crystal oscillators by the three-cornered-hat method. The observed fractional frequency fluctuations for an averaging time of 1 s were 6.3 ± 3.7 x 10⁻¹⁴, which is lower than the results from the best room temperature masers. In conjunction with the stability measurements, the phase noise of the maser electronics was investigated. In particular, the temperature dependence of the phase noise of the cooled preamplifier was measured and it was shown that anomalous high noise levels between 2.2 K and 4.2 K are caused by the boiling of the liquid helium. From the temperature dependence of the maser frequency, the binding energy E[sub B] of H on ⁴He could be determined to a high precision. The result is E[sub B] = 1.011 ± 0.010 K. An extensive computer simulation program has been written that models the operation of the cryogenic hydrogen maser. It has been used to analyze and interpret some of the data. In addition, this simulation program is helpful for the design of an improved second generation cryogenic maser. Based on the present data and the model calculations, a new pumping scheme is proposed that is expected to increase the efficiency of the state invertor significantly.Science, Faculty ofPhysics and Astronomy, Department ofGraduat