  He-Ne lasers have been one of the most widely employed optoelectronic
elements, playing irreplaceable roles in various applications, including
optical detections, spectroscopy, interferometry, laser processing, and so on.
For broad applications that require single-mode operations, the gain linewidth
needs to be constrained, which conventionally can be obtained through overall
gain suppressions. Such an approach inevitably has limited the output power and
thus restricted further applications that require ultra-high precisions. In
this article, we discover that inelastic collisions among He and Ne atoms can
be exploited to cool down the Ne atoms, compressing the Doppler broadening and
consequently also the gain linewidth, enabling us to further experimentally
demonstrate a significantly broadened spectral range of single-mode operation
with stable output powers. Our discovery of inelastic collision-induced atomic
cooling has ultimately overcome the tradeoff between output power and gain
linewidth, opening new avenues for both fundamental explorations and disruptive
applications relying on gaseous laser systems.
