Geometric-Phase-Lens Collimated Vertical-Cavity Surface-Emitting Laser Turned on Rb D Line for Miniature Atomic Magnetometers

We report on the geometric-phase (GP)-lens collimation of commercially available vertical-cavity surface-emitting laser (VCSEL), performed in the Rb D1 line spectroscopy experiments. The GP lens is fabricated by the direct-write approach and employed photopatterned liquid crystals in thin films to control the geometric phase shift. It generates the positive and negative first-order diffraction of laser beam, which are spatially separated to two focal points with one focused and the other one defocused. The diffraction efficiency at 794.9 nm is up to 99%. Changing the polarization state of the incident VCSEL laser continuously, the collimation and polarization conversion of divergent VCSEL laser is accomplished via GP lens. The + and components of circularly polarized light are separated via different diffraction orders, which suppresses the light shift in atomic atoms. Then, a compact atomic magnetometer (AM) is constructed based on a Rb microcell. High sensitivity up to 30 fT/Hz 1/2 is achieved in the single-beam configuration. It is expected that directly fabricating the liquid crystal film on the surface of vapor cells can further reduce the sensor volume. This work extends integrated photonics to atomic spectroscopy and spin-based sensing and of great significance to promote the application of miniature AMs in biomagnetic measurements.