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Optics Letters

Exploration of a vapor cell optical frequency standard scheme implemented using Doppler-free spectroscopy

Ang Zhang, Yuechen Zhang, Weihao Zhao, Yuan Tian, Yi Zhang, Sihong Gu, Jie‐Hua Chen

Published Sep 9, 2024• 5 citations
Publisher

Abstract

We implement a compact optical frequency standard scheme with laser frequency locked to the 5 S 1/2 ( F = 2) − 6 P 3/2 ( F ′ = 3) transition of the second excited state of 87 Rb atoms in a 3 mm cubic glass cell, using a Doppler-free saturated absorption spectroscopy. The experimental results show the frequency stability at the level of 2.2 × 10 −12 at 1 s. Furthermore, we conduct an experimental study on the effect of a repump laser on the frequency performance of the saturated absorption spectroscopy optical frequency standard, providing valuable experimental results with reference values for implementing this type of optical atomic clock.

DOI
10.1364/ol.534239

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•Jun 21, 2021•0 citations
We implement a compact optical frequency standard scheme with laser frequency locked to the 5 S 1/2 ( F = 2) − 6 P 3/2 ( F ′ = 3) transition of the second excited state of 87 Rb atoms in a 3 mm cubic glass cell, using a Doppler-free saturated absorption spectroscopy. The experimental results show the frequency stability at the level of 2.2 × 10 −12 at 1 s. Furthermore, we conduct an experimental study on the effect of a repump laser on the frequency performance of the saturated absorption spectroscopy optical frequency standard, providing valuable experimental results with reference values for implementing this type of optical atomic clock.
Abstract Locking laser frequencies to Doppler-free spectra produced by the interaction of light with alkali atoms in a vapor cell is a promising approach for realizing compact atomic optical frequency reference. In this work, we employ counter-propagating monochromatic laser beams with a polarization angle of 45° to interact with 87 Rb atoms in a 3 mm cubic vapor cell, inducing coherent resonance. By detecting the laser polarization rotation, we obtain a Doppler free spectral line, which is used as a reference for laser frequency locking, thus realizing an optical reference. We build two nominally identical systems and measure their beatnote, yielding a fractional frequency stability of 5.3×10 -13 at 1 s. This study demonstrates that the proposed scheme is a competitive approach for realizing high performance compact atomic optical reference.
We experimentally study the character of saturated absorption spectroscopy (SAS) of the 87 Rb 5 S 1/2 → 6 P 3/2 transition at 420 nm in a miniature cubic glass cell (3 × 3 × 3 mm 3 ). The influences of the laser intensity and cell temperature on the saturated absorption resonance are comprehensively investigated to determine the optimal parameters for a compact stabilized frequency standard. By stabilizing the laser frequency to the optimized SAS signal, a beatnote stability of 2.4 × 10 −13 at 1 s is measured between two identical SAS systems, corresponding to a single-laser stability of 1.7 × 10 −13 at 1 s, assuming equal contribution from each laser. A further analysis of the noise budget reveals that the main contributions of short-term stability arise from the intermodulation effect and the laser frequency noise through the frequency modulation to amplitude modulation (FM-AM) conversion process. Our work provides a promising route toward high-performance miniaturized optical frequency standards based on high-lying excited-state transitions.
This study investigates the application of miniature quantum references within small-scale optical atomic frequency standards, utilizing a diminutive 87 Rb glass cell, dimensions of 6 mm × 6 mm × 6 mm, to establish a quantum frequency standard.By employing the transition spectrum from 5 2 S 1/2 F = 2 to 5 2 P 3/2 F 0 =3, this study successfully demonstrates the development of a compact rubidium atomic optical frequency standard via modulation transfer spectroscopy (MTS).Subsequent to frequency stabilization, the 780 nm clock laser exhibits a linewidth of 6.9 kHz, and its out-of-loop short-term stability reaches 4.1 × 10 -13 @ 1 s, as confirmed through beat frequency analysis.This research not only provides a practical blueprint for the development of small optical atomic frequency standards but also lays down essential groundwork for future advancements in chip-level optical frequency standard technologies.
Vapor-cell spectroscopy is an essential technique in many fields and is particularly relevant for quantum technologies. Most atom- and ion-trapping experiments rely on simultaneous spectroscopy of two atomic transitions, employing a separate apparatus for each transition. We demonstrate simultaneous spectroscopy on two atomic transitions, within a single apparatus, using spatially overlapped beams from two independent lasers. This method enables compact setups and offers superior spectroscopic performance, leading to sharper spectroscopy peaks, stronger absorption signals, and superior laser stability. Doppler-free locking features become accessible over a frequency range several hundred megahertz wider than for standard saturated absorption spectroscopy. Exploring the full parameter space associated with dual-frequency spectroscopy reveals a latticelike structure of sharp resonance features, which enhances experimental versatility by allowing laser frequency stabilization within a wide manifold of locations in two-dimensional frequency space. We present data for 133Cs^{133}\mathrm{Cs}133Cs and 85Rb^{85}\mathrm{Rb}85Rb and compare our results to a theoretical model. Employing the technique for frequency stabilization close to the D2{D}_{2}D2​ line of 85Rb^{85}\mathrm{Rb}85Rb results in an improvement in frequency stability by a factor typically between 2 and 3 for averaging times of up to 1 s. The technique will advance portable quantum technologies and facilitate high-precision measurements.
Abstract We report on the characterization of Doppler-free resonances detected by probing the 5S 1/2 → 6P 3/2 transition of the 87 Rb atom at 420 nm. Compared to the commonly studied 5S → 5P transition, the 5S → 6P transition offers advantages of higher transition frequency and narrower natural linewidth. We investigate how the pump laser intensity and cell temperature affect the linewidth and amplitude of the saturated absorption signal for the 420-nm second excited state transition 5S 1/2 ( F = 2) → 6P 3/2 in 87 Rb atoms. Furthermore, we introduce a 795-nm repump laser to improve the quality of the saturated absorption signal. At a relatively low vapor cell temperature of 43 °C, the amplitude-to-linewidth ratio increased by 110%. These results are highly relevant for the development of stable ultraviolet laser sources and their associated applications.
Vapour-cell spectroscopy is widely used for the frequency stabilisation of diode lasers relative to specific atomic transitions - a technique essential in cold atom and ion trapping experiments. Two laser beams, tuned to different frequencies, can be overlapped on the same spatial path as an aid to compactness; this method also enhances the resulting spectroscopic signal via optical pumping effects, yielding an increase in the sensitivity of spectroscopically-generated laser stabilisation signals. Doppler-free locking features become visible over a frequency range several hundred MHz wider than for standard saturated absorption spectroscopy. Herein we present the measured Doppler-free spectroscopy signals from an atomic vapour cell as a function of both laser frequencies, showing experimental data that covers the full, 2D parameter space associated with dual-frequency spectroscopy. We consider how dual-frequency spectroscopy could be used for enhanced frequency-stabilisation of one laser, or alternatively to frequency-stabilise two lasers simultaneously, and analyse the likely performance of such stabilisation methods based on our experimental results. We discuss the underlying physical mechanism of the technique and show that a simple rate-equation model successfully predicts the key qualitative features of our results