In a spin-exchange-relaxation-free (SERF) atomic magnetometer with ultrahigh sensitivity, the ac-Stark shift generated by circularly polarized light results in the attenuation of the SERF atomic magnetometer response, and the virtual magnetic field gradient induced by the ac-Stark shift can reduce the sensitivity of the SERF atomic magnetometer. In this paper, we use a hybrid optical pumping method to address the ac-Stark shift problem. By switching between left-hand and right-hand circularly polarized lights and compensating the residual magnetic field of the magnetometer, the ac-Stark shift could be reduced and then suppressed effectively.

Alkali metal atomic cells are crucial components of atomic instruments, such as atomic magnetometers, atomic gyroscopes, and atomic clocks. A highly uniform and stable heating structure can ensure the stability of the alkali metal atom density. The vapor cell of an atomic magnetometer that uses laser heating has no magnetic field interference and ease of miniaturization, making it superior to hot air heating and AC electric heating. However, the current laser heating structure suffers from low heating efficiency and uneven temperature distribution inside the vapor cell. In this paper, we designed a non-magnetic heating structure based on the laser heating principle. We studied the temperature distribution of the heating structure using the finite element method (FEM) and analyzed the conversion and transfer of laser energy. We found that the heat conduction between the vapor cell and the heating chips (colored filters) is poor, resulting in uneven temperature distribution and low heating efficiency in the vapor cell. Therefore, the addition of graphite film to the four surfaces of the vapor cell was an important improvement. This addition helped to balance the temperature distribution and improve the conduction efficiency of the heating structure. It was measured that the power of the heating laser remained unchanged. After the addition of the graphite film, the temperature difference coefficient (CVT) used to evaluate the internal temperature uniformity of the vapor cell was reduced from 0.1308 to 0.0426. This research paper is crucial for improving the heating efficiency of the non-magnetic heating structure and the temperature uniformity of the vapor cell.

A parallel-fiber-loop interferometer based on Vernier effect is proposed to detect strain and temperature. The interference generates between the outputs of two parallel fiber Sagnac interferometers (PSIs). Each SI is inserted into a polarization-maintaining fiber (PMF) with the same type but different length. The feasibility of the system is proven theoretically and experimentally. In the interference spectrum, it is observed that the sensor has clearer upper and lower limits than the cascade structure, which is more beneficial to track the drift of spectral envelope. Experimental results showed that the strain sensitivity increased from 8.13 pm/ $\mu \varepsilon $ for the single SI to 61.98 pm/ $\mu \varepsilon $ for the PSIs. The temperature sensitivity increased from −1.51 nm/°C for the single SI to −14.32 nm/°C for the PSIs and the magnification is amplified eight times. The device has the advantages of simple structure, low cost, high sensitivity, and good stability, which has a good application prospect in strain and temperature measurement.

A reflected atomic magnetometer with single beam is described in this study. A single beam propagates forward for polarizing the atoms and backward for detecting Larmor precession after reflection. The feasibility of the system was studied theoretically and experimentally and compared with the single beam with ellipticity. In reflected scheme, high pump efficiency ensures a reduced power and more flexible operating wavelength considering the AC Stark shift, pump efficiency, and probe signal. The nonuniform optical rotation distribution along the cell was also analyzed. The wavelength of the system was optimized to 795.3 nm. The magnetic field sensitivity of the system is achieved to be 600 fT/Hz ^1/2 and the experimental bandwidth was 17 Hz. The compact design enables new possibility of the atomic magnetometer for magnetoencephalography systems.

Surface plasmon resonance (SPR) sensors have been widely applied in many fields because of their advantages of working in real time and high sensitivity. However, because the spectrum of an SPR sensor is easily affected by the smoothness of the metal surface, this type of sensor has obvious disadvantages in the application of quantitative detection. We designed an SPR refractive index sensor for molecular detection that has the advantage of quantifiability. A ratio spectral quantitative analysis method was established based on the two coherent dips of the SPR spectrum formed by the strong coupling effect between the surface plasmon polaritons and the excitons of the J-aggregate molecule 5,6-dichloro-2–[3–[5,6-dichloro-1-ethyl-3–(4-sulfobutyl)–2-benzimidazoline subunit] propenyl]–3-ethyl-1–(4-sulfobutyl) benzimidazole hydroxide inner salt (TDBC). The introduced MoS₂/graphene van der Waals heterojunction produced an effective charge transfer to the Ag film, resulting in significant electric field enhancement at the sensing interface and further improving the detection sensitivity of the sensor. The simulation results showed that for 43 nm Ag film, for example, the ratiometric SPR sensor with the Ag film structure can obtain 16.12 RIU⁻¹ sensing sensitivity, applied to the detection of gas molecules, while the SPR sensor with single-layer graphene and three layers of MoS₂ heterostructures can obtain 50.68 RIU⁻¹ sensing sensitivity. The addition of van der Waals heterostructures can significantly improve sensing performance by 215%.