ABSTRACT
An adjustable optical vortex array (OVA) based on decentered annular beam pumping has been demonstrated in an end-pumped Nd:YVO4 laser. This method allows for not only the transverse mode locking of different modes, but also the ability to adjust the mode weight and phase by manipulating the position of the focusing lens and axicon lens. To explain this phenomenon, we propose a threshold model for each mode. Using this approach, we were able to generate optical vortex arrays with 2-7 phase singularities, achieving a maximum conversion efficiency of 25.8%. Our work represents an innovative advancement in the development of solid-state lasers capable of generating adjustable vortex points.
ABSTRACT
In this Letter, we propose a single-beam nonlinear magneto-optical rotation (NMOR) magnetometer with a multipass 4He gas-discharged cell. In contrast to the single-pass cell, the multipass cell allowed laser beams to pass through the metastable-state atomic ensemble 22 times, which directly increases the optical path length and significantly enhances magneto-optical rotation in the 4He gas sample. Based on nonlinear Faraday rotation, the 4He magnetometer with the multipass cell demonstrates a noise floor of 9 fT/Hz1/2, which approaches the photon-shot noise floor limit of 6.4 fT/Hz1/2. In addition, the wider linewidth in metastable-state atoms realizes an NMOR 4He magnetometer with a 3 dB bandwidth of 4.3 kHz, in contrast to the ultranarrow linewidth in the antirelaxation-coated cells or spin-exchange relaxation-free regime alkali-metal cells with buffer gas. Since the 4He cell functions without heating or cryogenic cooling, the femtotesla sensitivity and kilohertz-bandwidth 4He magnetometer exhibits potential in biomagnetic applications such as magnetocardiography and magnetoencephalography.
