Semiconductor laser excitation of Ramsey fringes by using a Raman transition in a cesium atomic beam

Recently there has been interest in the use of the laser slowed and trapped atoms for the development of high-accuracy atomic clocks.'` For slow-atom clocks, employing separated field excitation, the use of a Raman transition may have advantages over direct microwave excitation.4 6 This is because the two-zone Raman interaction has the demonstrated ability to reverse the sign of the ac Stark shift.7 This property may be useful as a technique to cancel ac Stark shifts that can be produced when atoms in the Ramsey dark zone interact with stray fluorescent light.8 Such dark zone interactions are likely to be important in slow-atom clocks because of the long dark zone transit times. Raman transitions are also of interest because the optical forces exerted by Raman resonant standing waves or related schemes may lead to the development of improved, high-density dark atom traps.9 "0 In this paper, we demonstrate that it is possible for one to excite narrow Raman-Ramsey fringes in a cesium beam, with a high signal-to-noise ratio, using a single, amplitudemodulated semiconductor laser. The ability to use a single semiconductor laser to replace a microwave cavity is also important for potential device applications. The laser-excited resonance Raman interaction is illustrated in Fig. 1. Here, long-lived states la) and lb) are coupled to a common excited state le) by laser fields at frequencies wl and ° 2, respectively. As is well known,"", 2