All-fiber-device-coupled compact, transportable ultra-stable laser

In response to the demand for operation in non-laboratory environments, there has been a trend toward the development of compact, transportable ultra-stable lasers. This paper reports on this sort of laser system assembled in a cabinet. The whole optical part utilizes fiber-coupled devices to simplify the integration. In addition, spatial beam collimation and alignment into the high-finesse cavity are realized by a five-axis positioner and a focus-adjustable fiber collimator, which significantly relax the alignment and adjustment. A theoretical analysis is performed on how the collimator adjusts the beam profile and coupling efficiency. The support structure of the system is specially designed as well so that it features robustness and transportation without performance degradation. The observed linewidth is 1.4 Hz within a duration of 1 s. After subtracting the linear drift of 70 mHz/s, the fractional frequency instability is better than 4 × 10^-15, for the averaging time ranging from 1 to 100 s, which is close to the thermal noise limit of the high-finesse cavity.