Abstract
We investigate the architecture of microfabricated vapor cells with reflective sidewalls for applications in chip scale atomic sensors. The optical configuration in operation is suitable for both one-beam and two-beam (pump & probe) schemes. In the miniaturized vapor cells, the laser beam is reflected twice by the aluminum reflectors on the wet etched 54.7° sidewalls to prolong the optical length significantly, thus resulting in a return reflectance that is three times that of bare silicon sidewalls. To avoid limitations faced in the fabrication process, a simpler, more universal and less constrained fabrication process of microfabricated vapor cells for chip scale atomic sensors with uncompromised performance is implemented, which also decreases the fabrication costs and procedures. Characterization measurements show that with effective sidewall reflectors, mm3 level volume and feasible hermeticity, the elongated miniature vapor cells demonstrate a linear absorption contrast improvement by 10 times over the conventional micro-electro-mechanical system (MEMS) vapor cells at ~50 °C in the rubidium D1 absorption spectroscopy experiments. At the operating temperature of ~90 °C for chip scale atomic sensors, a 50% linear absorption contrast enhancement is obtained with the reflective cell architecture. This leads to a potential improvement in the clock stability and magnetometer sensitivity. Besides, the coherent population trapping spectroscopy is applied to characterize the microfabricated vacuum cells with 46.3 kHz linewidth in the through cell configuration, demonstrating the effectiveness in chip scale atomic sensors.
Highlights
Atomic sensors, which are based on atomic spectroscopy and light-atom interaction, serve as precision measurement sensors in various applications [1,2]
The sensitivity of the spin exchange relaxation free (SERF) atomic magnetometer has surpassed that of the superconducting quantum interference device (SQUID), which is known as the state-of-the-art most sensitive magnetometer [5]
Based on MEMS technology and integrated optics, the proposed vapor cell is suitable for single-beam applications, such as atomic clocks, as well as pump-and-probe-beam applications, such as atomic magnetometers
Summary
Atomic sensors, which are based on atomic spectroscopy and light-atom interaction, serve as precision measurement sensors in various applications [1,2]. In order to miniaturize the atomic clock, the principle of coherent population trapping (CPT) is more widely implemented than improving the conventional optical-microwave scheme, such as the microloop-gap resonator [8,9] This principle only requires a simple physical architecture and promises compatibility with the MEMS technology. The vapor cells can be batch-fabricated, while all optics, including the vertical cavity surface emitting laser (VCSEL), can be integrated as small as cm to mm in volume These apply to atomic magnetometers, operating in the CPT structure, traditional optical pumping regimes, or even SERF technology, leading to the investigation of chip scale atomic magnetometers [10,11]. Characterization and measurement of microfabricated vapor cells have verified their improved performance in terms of reflection efficiency, linear absorption contrast, CPT contrast, etc Such vapor cells, with low fabrication costs and improved performance, are promising in chip scale atomic sensor applications
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