A new method for narrowing laser linewidths could enable precision sensors in portable forms. Based on Rayleigh backscattering, the technique effectively compresses a laser linewidth to as low as 130 Hz and side mode suppression up to 75 dB. It uses a single-longitudinal-mode fiber ring laser using a self-rejection feedback structure at room temperature. Until now the same results have only been possible using highly scattering structures under extremely quiet conditions underground. “It can be used to synthesize more complex optical signals, even the (terahertz) signal and microwave signals,” said Dr. Tao Zhu of Chongqing University. “And it can also provide technical support for precision sensing fields such as high-resolution laser spectroscopy, optical atomic clocks, gravitational wave detection and low-noise microwave signal generation.” The research was published in the Chinese Science Bulletin (doi: 10.1007/s11434-014-0603-0).