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arXiv:2509.20619 · Optics Letters

Sub-Doppler spectroscopy of the strontium intercombination line in a microfabricated vapor cell

Yang Li, John E. Kitching, Matthew T. Hummon

Published Dec 8, 2025• 1 citation
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Abstract

We report a 100 kHz linewidth for the 1 S 0 to 3 P 1 intercombination line of 88 Sr atoms at 689 nm in a microfabricated (9×14×4.4) mm 3 vapor cell. This puts an upper bound on the residual gas pressure in the vapor cell of 10 mTorr. The microfabricated Sr vapor cell offers an inexpensive and scalable way to lock lasers in state-of-the-art cold-atom-based atomic clocks and quantum computing experiments. It also paves the way for compact and precise optical frequency references based on alkaline earth vapor cells.

DOI
10.1364/ol.579933

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Optics Letters•Mar 5, 2024•16 citations
We report a 100 kHz linewidth for the 1 S 0 to 3 P 1 intercombination line of 88 Sr atoms at 689 nm in a microfabricated (9×14×4.4) mm 3 vapor cell. This puts an upper bound on the residual gas pressure in the vapor cell of 10 mTorr. The microfabricated Sr vapor cell offers an inexpensive and scalable way to lock lasers in state-of-the-art cold-atom-based atomic clocks and quantum computing experiments. It also paves the way for compact and precise optical frequency references based on alkaline earth vapor cells.
We demonstrate strontium (Sr) atomic vapor cells having a total external volume of 0.63 cm 3 that can operate above 300 °C for times exceeding 380 h. The cells are fabricated using micromachined silicon frames anodically bonded to glass windows that have a 20-nm thick protective layer of Al 2 O 3 deposited on the interior surfaces. The presence of Sr vapor in the cell is confirmed through laser absorption spectroscopy for the 1 S 0 → 1 P 1 transition in Sr at 461 nm. Measurements of sub-Doppler linewidths indicated negligible (<3 MHz) broadening of this transition from residual background gas collisions. This compact and manufacturable, high-temperature atomic vapor cell can enable narrow-line optical frequency references based on strontium and other alkaline earth species.
Microfabricated (MEMS) alkali vapor cells are at the core of high-precision integrated atomic quantum sensors and devices [1], such as microwave and optical clocks, or magnetometers. The first chip-scale atomic device was a microwave atomic clock based on coherent population trapping [2]. It has offered in its industrial and commercialized version an ultra-low size-power -instability budget, impacting a plethora of industrial and scientific applications. Nevertheless, the short-term stability of these clocks is usually limited at about 10−10 at 1 s. Hot vapor MEMS-based optical frequency standards constitute a new generation of miniaturized clocks, with enhanced stability. These references keep the benefit of using wafer-scalable and mass-producible vapor cells while preventing ultra-high vacuum technologies and laser cooling. Among the transitions explored, the 6S1/2 → 7P1/2 near-UV transition of Cs atom was used to demonstrate an optical reference with a stability of 2.1 × 10−13 at 1 s and averaging down to a few 10−14 [3]. However, this reference was based on a 5 cm-long glass-blown cell, not compliant with the advent of a fully-miniaturized and low-power optical clock. In this work [4], we present the characterization of sub-Doppler resonances detected in a microfabricated cell by probing, in a simple saturated absorption configuration, the Cs atom 6S1/2 → 7P1/2 transition at 459 nm. The impact of the laser intensity and cell temperature on the sub-Doppler resonance is experimentally investigated. Optimal values are identified for the development of a near-UV microcell-stabilized frequency reference. Detection noise measurements are also reported, predicting a short-term stability in the 10−13 range at 1 s. Tests of cells with embedded getters are under progress for improved purity of the cell inner atmosphere and narrowing of the resonance.
We report on the characterization of sub-Doppler resonances detected by probing the 6S1/2 - 7P1/2 transition of the Cs atom at 459 nm in a microfabricated vapor cell. The dependence of the sub-Doppler resonance (linewidth, amplitude) on some key experimental parameters, including the laser intensity and the cell temperature, is investigated. These narrow atomic resonances are of interest for high-resolution spectroscopy and instrumentation and may constitute the basis of a high-stability microcell optical standard.