The Effect of Laser Line-narrowing on the Performance of Optically Pumped Cesium Atomic Beam Frequency Standards

An experiment has been conducted to investigate the effect of laser line-narrowing on the performance of an optically pumped cesium beam frequency standard. A two laser scheme (4-+4'u for optical pumping and 4+5'7t. for detection) was used and the lasers were either frequency locked to Cs saturated absorption features in an external cell or linenarrowed by optical feedback from an external Fabry'Perot cavity [ l ] . Relative to the frequency stabilization to the saturated absorption the line-narrowing on the detection laser produced a large improvement (+14dB) in the signal-to-noise ratio (S/N). However, line-narrowing on both pump and detector lasers was necessary to achieve beam shot noise limited performance. The S/N and line Q achieved in these experiments should result in a clock stability of uy (~)=3-5~10-'~ T ' / ' [ 2 1 . INTRODUCTION The use of diode lasers for optical state preparation and detection in atomic beam frequency standards holds great promise for improvement in both the short term and long term performance of these standards. The potential for improved short term performance lies in the improved utilization of the atomic beam flux. A number of laboratories have begun experiments on optically pumped standards and the improved signal levels have been demonstrated. However, the potential signal-to-noise ratio (S/N) available has not previously been achieved when semiconductor lasers have been used as the optical source. This seems to be due to residual FM noise in the laser sources