Reducing the light-shift in the diode laser pumped rubidium atomic clock

One impediment to achieving the promise of enhanced laser-pumped gas cell clock performance resides with the light-shift effect, a phenomenon whereby diode laser optical frequency fluctuations are mapped onto the atomic clock's output frequency. The alternative to tightly stabilizing the diode laser in order to overcome this problem is to develop means of reducing the actual magnitude of the light-shift. Here, we briefly review two strategies for accomplishing this, and introduce a new one based on optical pumping with laser-induced-fluorescence (LIF). The advantage of LIF optical pumping is that the clock's output frequency is insensitive to laser frequency fluctuations. Though LIF optical pumping creates a dependence of clock frequency on laser intensity variations, it is to be noted that diode lasers have very low intensity noise. Consequently, with regards to the light-shift effect the LIF strategy takes advantage of an inherent diode laser strength.