Laser Frequency Stabilization for Atom Interferometry Applications

Many atomic sensors depend on using a laser with a precisely defined frequency. Unfortunately, most lasers suffer from perturbations in their effective cavity length (which determines the operating frequency of the laser) and active stabilization is required. The atomic interferometry lab at NPS currently uses a laser locking system that has two major problems: The method to determine the desired frequency is not only frequency-sensitive but also intensity-sensitive and the bandwidth of the feedback is too low. The first step in controlling the laser frequency is to find the desired frequency. This value is usually found by taking the midpoint of a transmission peak that is obtained from a doppler-free absorption spectrometer. Currently, this value is the reference frequency for the control system. The current method to determine this reference creates the drawbacks outlined above. To alter the transmission spectrum in a way that eliminates these errors, it is possible to modulate the laser frequency while slowly sweeping across anatomic absorption spectrum. By modulating the signal, the frequency band of the error signal increases which eliminates low frequency noise and thereby improves the accuracy. The modulated signal can then be used to create a new error signal that is used in a feedback system. Once the error signal is defined, it is then used to create a higher speed feedback loop which became limited to 1kHz.