A dual-wavelength continuous-wave mirrorless laser in thermal rubidium vapor

Abstract

Mirrorless lasers avoid cavity-pulling effects by generating stimulated emission directly from an atomic gain medium without an optical cavity. However, most superradiant or superfluorescent emissions are transient, limiting their use as steady atom-referenced optical sources. Here, we demonstrate a continuous-wave dual-wavelength mirrorless laser in thermal rubidium vapor. A frequency-stabilized 420 nm laser pumps the 5S1/2→6P3/2 transition and generates directional infrared lasing at 1323 and 1367 nm through the non-cascaded 6S1/2→5P1/2 and 6S1/2→5P3/2 transitions. The emissions exhibit threshold-like pump-power dependence and a near-fundamental transverse mode, supporting CW mirrorless laser in a traveling-wave atomic gain medium. Heterodyne detection gives a 1367 nm linewidth of 32.5 kHz, which is 38 times narrower than the natural linewidth. This work establishes a linewidth-narrowed, cavity-free, atom-referenced dual-wavelength laser platform for precision spectroscopy, optical frequency references, and quantum sensing.