Red narrow-linewidth lasing and frequency comb from gain-switched self-injection-locked Fabry-Perot laser diode

Narrow-linewidth lasers are in extensive demand for numerous cutting-edge applications. Such lasers operating at the visible range are of particular interest. Self-injection locking of a laser diode frequency to a high-Q whispering gallery mode is an effective and universal way to achieve superior laser performance. We demonstrate ultranarrow lasing with less than 10 Hz instantaneous linewidth for 20 mu s averaging time at 638 nm using a Fabry-Perot laser diode locked to a crystalline MgF2 microresonator. The linewidth measured with a beta-separation line technique that characterizes 10 ms stability is as low as 1.4 kHz. Output power exceeds 80 mW. Demonstrated results are among the best for visible-range lasers in terms of linewidth combined with solid output power. We additionally report the first demonstration of a gain-switched regime for such stabilized Fabry-Perot laser diode showing a high-contrast visible frequency comb generation. Tunable linespacing from 10 MHz to 3.8 GHz is observed. We demonstrated that the beatnote between the lines has sub-Hz linewidth and experiences spectral purification in the self-injection locking regime. This result might be of special importance for spectroscopy in the visible range.

Automated summary

This study demonstrates the generation of ultranarrow linewidth lasers in the visible range by locking a Fabry-Perot laser diode to a crystalline MgF2 microresonator. The achieved low linewidth and high output power make it suitable for cutting-edge applications.