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Realizing always atomic translation frequency output, single-mode, high frequency stability, narrow linewidth semiconductor lasers, is one of the ultimate visions of areas related to quantums, such as quantum precision measurement and atomic physics. A single-mode Cs atom 852 nm Faraday laser, utilizing a corner cube retroreflector as the feedback element, is demonstrated and termed as a corner-cube-feedback Faraday laser. Its output frequency remains close to the Cs atomic Doppler-broadened transition line, and through the optimization of the working parameters of Faraday anomalous dispersion optical filter (FADOF), the laser output mode can still remain single, even though the diode current changes from 55 mA to 155 mA (with incremental step of approximately 2 mA) and the diode working temperature varies from $11.8 \,\mathrm{^{\circ }C}$ to $37.2 \,\mathrm{^{\circ }C}$ (with incremental step of approximately $3.5 \,\mathrm{^{\circ }C}$). Also, the single-mode laser oscillation can be achieved over a substantial angular range, specifically between +3$\mathrm{^{\circ }}$and −3$\mathrm{^{\circ }}$, where the angle is defined as the deviation of the incident light from the optical axis of the corner cube. Using the corner-cube retroreflector as external cavity feedback element, the environmental compatibility and reliability can be improved due to the precise reflection of the incident light beam back to its original direction. The most probable linewidth is 8 kHz measured by heterodyne beating with two identical lasers. The output power can achieve a maximum of 57 mW at 155 mA. As for the noise performance of the laser, the typical value of relative intensity noise (RIN) at 10 kHz is lower than −134 dBc/Hz. The pahse noise of the laser is superior than the commerical product. This single-mode corner-cube-feedback Faraday laser can be widely used in quantum precision measurement, such as atomic clocks, atomic gravimeters, and atomic magnetometers, etc.

Atomic optical filters such as Faraday anomalous dispersion optical filters (FADOFs) or similar technologies can achieve very narrow optical bandwidth close to the scale of atomic linewidth, which can be greatly reduced in cold atoms. However, limited by the number of cold atoms and the size of the cold atomic cloud, the number of atoms interacting with the laser is reduced, and the transmission remains as low as 2%. In this work, we introduce the optical pumping into the cold atomic optical filter to solve this problem. Circular polarized optical pumping can produce polarization of the atomic ensemble and induce dichromatic as well as the Faraday rotation. We demonstrate a cold-atom optical filter which operates on the 87Rb 52S1/2 (F=2) to 52P3/2 (F′=2) transition at 780 nm. The filter achieves an ultranarrow bandwidth of 6.6(4) MHz, and its peak transmission is 15.6%, which is nearly 14 times higher than that of the cold-atom optical filter realized by Faraday magneto-optic effect. This scheme can be extended to almost all kinds of atomic optical filters and may find applications in self-stabilizing laser and active optical clock.