Saturated Absorption Spectroscopy in Deep Space Atomic Clocks

Modern deep space atomic clocks have a time resolution of 10-15s, and OAISC aims to improve that time resolution by one to three orders of magnitude. With this sensitivity, space flight operations can have higher levels of autonomy, improve GPS signals, establish navigation networks on the moon for the Artemis missions, and even test fundamental physics, such as general relativity. What sets this clock apart from current deep space clocks is that it is an optical clock, meaning it uses light as its oscillator and a single strontium ion as its reference. However, to perform the necessary measurements, the strontium ion must be at sub-nanokelvin temperatures. This cooling is done using lasers, dubbed cooling lasers that must be tuned to specific frequencies in order to keep the atom at such low temperatures. In my presentation I will discuss how we used saturated absorption spectroscopy to maintain the laser at such specific frequencies. We demonstrate laser stability of 10-2 GHz, which is within the range needed to cool the atom.