Narrowing Laser Linewidth Using Modulation Transfer Spectroscopy

This paper provides a feasible method to narrow the linewidth of the laser by modulation transfer spectroscopy, benefiting from a high feedback bandwidth and the high signal-to-noise ratio of the spectroscopy. We experimentally stabilize the frequency of a 420 nm blue diode laser with a free-running Lorentz linewidth of 43 kHz on the quantum transition of 85Rb, and the heterodyne experiments based on two identical configurations showing that the linewidth of laser is efficiently narrowed by 6 times, namely a Lorentz linewidth of 7 kHz. With the feedback bandwidth and signal-to-noise ratio in-loop further enhanced, the scheme with a relatively simple construction can potentially achieve a sub-kHz laser linewidth.