Design and realization of beam collimation system for semiconductor laser in atomic magnetometer

Atomic magnetometer which uses alkali atoms as the sensors can realize ultrahigh sensitivity magnetic field measurement and has extensive applications scientific researches. Semiconductor lasers are used as the pump and probe laser in atomic magnetometer. Due to structural characteristics of semiconductor laser, beam divergence angles in vertical and horizontal direction have large deviation and laser beam diverges extremely fast. However, poor laser beam affects the implementation of atomic magnetometer sensitivity adversely. Only the circular laser beam with Gaussian distribution guarantees the homogeneous polarization of alkali atom vapor and high efficiency of atomic magnetometer. Consequently, a beam collimation system must be designed. In this paper, a collimation method using a thin lens and a pair of anamorphic prisms is proposed to guarantee the laser spot size approximately constant. The thin lens is used to decrease fast-axis divergence angle and ensure transmitted light is parallel. The anamorphic prisms pairs expand the laser beam in slow-axis and make the beam spot nearly round. Initially, the effect of thin lenses and anamorphic prisms on the relationship of input and output beam profiles is theoretically analyzed based on principle of geometrical optics. Then the software Zemax is used to simulate the collimation system. Finally, a beam collimation system is designed and tested. The experiment result shows that the laser beam size is approximately 2×2cm² and the beam approximate a Gaussian profile, which can meet the requirement of the atomic magnetometer.