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European Frequency and Time Forum

Frequency Shift Properties of 1S0-1P1 Transition of a Calcium Beam Optical Clock

Yu Chen, Yabei Su, Lei Han, Junfeng Ge, Xiaobo Xue, Shengkang Zhang

Published Jun 25, 2024• 0 citations
Publisher

Abstract

The narrow linewidth of1S0-3P1657 nm clock transition makes it a promising quantum frequency reference. In this experiment, the fast1S0-1P1423 nm transition is used to detect the narrow1S0-3P1657 nm clock transition. Therefore, the frequency stability of the 423 nm laser determines the performance of the optical frequency standard. Here we investigate the frequency shift properties of the neutral calcium atoms'1S0-1P1transition at 423 nm. We measure the frequency shift caused by temperature, laser power, and laser beam pointing.

DOI
10.1109/eftf61992.2024.10722682

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The narrow linewidth of1S0-3P1657 nm clock transition makes it a promising quantum frequency reference. In this experiment, the fast1S0-1P1423 nm transition is used to detect the narrow1S0-3P1657 nm clock transition. Therefore, the frequency stability of the 423 nm laser determines the performance of the optical frequency standard. Here we investigate the frequency shift properties of the neutral calcium atoms'1S0-1P1transition at 423 nm. We measure the frequency shift caused by temperature, laser power, and laser beam pointing.
The optical frequency transitions with long-lifetime spin triplet states produced by the two valence electrons in the outermost layer of alkaline earth atoms make calcium atom a promising quantum frequency reference. Electron-shelving detection improves the signal-to-noise ratio of the clock transition spectrum, enabling a calcium atomic beam optical frequency standard. This scheme employs the 1S0-1P1 transition at 423 nm to detect the 1S0-3P1 transition at 657 nm, emphasizing the importance of 423 nm laser stability. While the performance of these clocks is well-studied, research on the atomic beam itself is limited. This study investigates frequency shifts in neutral calcium atoms’ 1S0-1P1 transition at 423 nm and their 1S0-3P1 transition at 657 nm. We measure the frequency shift caused by temperature, laser power, and laser alignment, providing insights to optimize the design of the calcium beam’s physical apparatus.
The Ca beam optical frequency standard has the potential to be small optical clock like small Cs beam clock in microwave regime. For improving the signal-to-noise ratio of the clock transition spectroscopy, the electron shelving detection, which uses the fast1S0-1P1423nm transition to detect the narrow1S0-3P1657nm clock transition, was applied for Ca beam optical frequency standard. Therefore the frequency stability of 423 nm laser to some extent determines the performance of the optical frequency standard. In this paper, we stabilize the 423 nm laser frequency to Ca beam signal with side-band locking technique and estimate the preliminary stability of 423 nm laser which is 1.4×10-11at 1 s and 2×10-12at 100 s.
With the aid of an optical frequency divider based on an optical frequency comb, the frequency of a laser at 431 nm is divided from a cavity-stabilized laser at 578 nm. Using the frequency-stabilized 431 nm laser, we observe a 2.5 kHz linewidth 4f146s2 1S0−4f135d6s2 (J = 2) transition of 171Yb atoms trapped in an optical lattice. By measuring the lattice-induced frequency shift, we determine the magic wavelength of the optical lattice for the 431 nm transition to be 797.97(20) nm. The frequency of the 431 nm transition is measured to be 695 171 054 856.9(1.1) kHz by referencing to the 1S0−3P0 transition at 578 nm of Yb atoms.
Research on the development of the optical frequency standard based on trapped and cold 40 Ca + with the 4s 2 S 1/2 -3d 2 D 5/2 clock transition at 729 nm is reported. A single calcium ion was trapped and laser cooled in the Paul trap and stay in trap for more than 15 days. The linewidth of a 729 nm laser was reduced to less than 10 Hz by locking to a cavity for longer than 50 hours uninterruptedly. The overall systematic uncertainty of the clock transition has been characterized to be better than 6.5×10 −16 . The absolute frequency of the clock transition was measured at 10 −15 level using an optical frequency comb referenced to a Hydrogen maser, which was calibrated to the SI second through the global positioning system (GPS). The frequency value was 411042129776393.0(1.6) Hz after the correction of the systematic shifts.
Single laser-cooled ions in radiofrequency traps can serve as the basis for highly stable optical frequency standards. Here we present recent results on In+, using the 1S0 yields 3P0 line at 236.5 nm wavelength as the clock transition. This resonance has a natural linewidth of only 0.82 Hz and systematic shifts should be controllable at the mHz level. A single indium ion is stored in a miniature Paul- Straubel trap and laser cooled to a temperature of about 100 (mu) K. The clock transition is excited using a frequency quadrupled 946 nm Nd:YAG laser. A fractional resolution of 1.3 (DOT) 10-13 has been achieved so far (linewidth of 170 Hz at 1267 THz). The absolute optical frequency of the clock transition has been measured with an uncertainty being less than 3 (DOT) 10-13 using a frequency chain and a methane-stabilized HeNe laser that was calibrated with a cesium clock.
Abstract Optical clocks with thermal atoms are characterized by compact size, simple structure, reduced weight, and low power consumption and have the potential for broad out-of-the-lab and commercial applications. Here, we demonstrate a 459 nm optical clock based on the 6S 1/2 –7P 1/2 transition in thermal 133 Cs atoms. Two methods, modulation transfer spectroscopy (MTS) and frequency modulation spectroscopy (FMS), are employed to stabilize the frequency of a 459 nm commercial laser to the atomic transition. The MTS-MTS and MTS-FMS beat-note measurements show short-term frequency stabilities of 3.7 × 10 − 13 / τ and 6.4 × 10 − 13 / τ , respectively, at the averaging time τ . The 459 nm passive optical clock further serves as the pump for an active 1470 nm optical clock based on the cavityless lasing. The resultant 1470 nm output power reaches over 10 μW and the pump-beam-induced light shift is estimated to be 2 π × 11 Hz with a fractional uncertainty of 2.4 × 10 −18 . These results demonstrate the feasibility of hybridizing passive and active optical clocks, providing a promising route toward compact multi-wavelength optical frequency standards.