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
⁸⁵
Rb, 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.