Performance measurement of unidirectional continuous-wave ring Ti:sapphire laser with self-injection locking and isolator-based configurations

Commercial isolators used in solid-state lasers are costly, suffer from high losses, and require precise alignment, while high-power pumping induces thermal lensing, limiting their application. In atomic magnetometry and inertial measurements under the Spin-Exchange Relaxation-Free (SERF) regime, which require low-intensity noise in the 0–100 Hz range from the pump laser, the self-injection method offers a promising alternative by achieving unidirectional operation with minimal loss. This work presents a continuous-wave (CW) ring Ti:sapphire laser that achieves unidirectional operation using either the self-injection method or a commercial isolator, and the laser performance under both methods was compared, with the free-running state used as a reference. The results show that self-injection improved unidirectionality without introducing additional losses, preserved the output wavelength and mode structures, and significantly suppressed intensity noise below 10 kHz, with minimal impact on higher frequencies. It also suppressed frequency noise from 1 Hz to 1 kHz and narrowed the linewidth. These findings underscore the self-injection method's role in low-frequency noise suppression in Ti:sapphire lasers and highlight its potential for advancing quantum precision measurements.