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A research team led by Prof. Zhang Tianshu at the Hefei Institutes of Â鶹ÒùÔºical Science of the Chinese Academy of Sciences has developed a compact all-solid-state continuous-wave (CW) single-longitudinal-mode (SLM) laser with high frequency stability using iodine-based frequency locking, advancing its application in atmospheric remote sensing and environmental monitoring. The study is in Optics and Laser Technology.

CW SLM lasers are widely used in areas such as laser amplification, gravitational wave detection, and quantum optics. They also play a key role in atmospheric remote sensing and environmental monitoring. These applications require not only SLM laser output but also high frequency stability, which current semiconductor and fiber lasers struggle to provide due to limited environmental adaptability.

In this study, the team introduced a ring resonator structure combined with iodine molecular absorption frequency locking technology. By locking the laser frequency to the flank of specific iodine absorption lines and employing feedback control to adjust the resonator length, they achieved long-term frequency stability.

The laser exhibits excellent beam quality, with M² values of 1.05 in the horizontal direction and 1.19 in the vertical direction, demonstrating high spatial coherence. Its output linewidth is less than 10 MHz, confirming stable single-longitudinal-mode operation. In terms of frequency stability, while the laser shows a drift of more than 200 MHz in free-running mode, this is significantly reduced to within 4 MHz over a continuous 7-hour period when frequency locking is applied.

To support future integration and field deployment, the team also engineered the system with a compact opto-mechanical-thermal-electrical design, meeting the requirements for miniaturization and stability.

This achievement is expected to provide a core laser source for next-generation environmental monitoring instruments, particularly in the detection of atmospheric pollutants and greenhouse gases, offering technical support for air quality assessment and climate change research, according to the team.