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Acta Physica Sinica

Experimentally studying the scheme on exciting coherent population trapping resonances with lin//lin configuration

Jing Yang, Liu Guo-Bin, Sihong Gu

Published Jan 1, 2012• 5 citations
Publisher

Abstract

Coherent population trapping (CPT) atomic clocks are prevailingly realized by exciting CPT resonance with circularly polarized bichromatic coherent light (σ+-σ+ scheme), while atom utilization efficiency is relatively low in the scheme. For improving efficiency, we experimentally study the scheme of realizing CPT resonance through the interaction between atoms and parallel linearly polarized bichromatic coherent light field (lin//lin scheme). In the same experimental conditions the experimental results show that the signal-noise ratio of the CPT resonance signal is twice, and the differential slope is 1.65 time higher than those of σ+-σ+ scheme. The experimental results reveal that the scheme is an ideal candidate for low power consuming atomic clock and magnetometer.

DOI
10.7498/aps.61.043202

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Coherent population trapping (CPT) atomic clocks are prevailingly realized by exciting CPT resonance with circularly polarized bichromatic coherent light (σ+-σ+ scheme), while atom utilization efficiency is relatively low in the scheme. For improving efficiency, we experimentally study the scheme of realizing CPT resonance through the interaction between atoms and parallel linearly polarized bichromatic coherent light field (lin//lin scheme). In the same experimental conditions the experimental results show that the signal-noise ratio of the CPT resonance signal is twice, and the differential slope is 1.65 time higher than those of σ+-σ+ scheme. The experimental results reveal that the scheme is an ideal candidate for low power consuming atomic clock and magnetometer.
We present an experimental and theoretical investigation of the coherent population trapping (CPT) resonance excited on the D1 line of 87 Rb atoms by bichromatic linearly polarized laser light. The experimental results show that a lin ‖ lin transition scheme is a promising alternative to the conventional circular—circular transition scheme for an atomic magnetometer. Compared with the circular light transition scheme, linear light accounts for high-contrast transmission resonances, which makes this excitation scheme promising for high-sensitivity magnetometers. We also use linear light and circular light to detect changes of a standard magnetic field, separately.
Traditional coherent population trapping (CPT) atomic clocks use single circularly polarized coherent multichromatic light to interact with atoms for preparing CPT dark states. While this configuration is simple, it suffers from the trap states and involves only the ±1st-order sidebands in the CPT resonance, excluding the carrier and other sidebands. This results in a lower CPT signal amplitude and higher laser noise, limiting the frequency stability of CPT atomic clocks. To address this issue, we developed and experimentally validated a scheme utilizing left- and right-circularly polarized light based on multiple coherent superpositions. This scheme significantly enhances the amplitude of the CPT resonance. Furthermore, by incorporating a Michelson interferometer, the polarization direction of the ±1st-order sidebands in the coherent multichromatic light is adjusted from parallel to perpendicular, enabling the filtering of one sideband to be detected while eliminating other unwanted sidebands and effectively suppressing laser noise. The results show that, under identical conditions, the short-term frequency stability of this method is theoretically improved by a factor of seven compared to the traditional circularly polarized light scheme, providing an effective pathway for the development of high-performance CPT atomic clocks.
We have experimentally demonstrated that magnetic-field-insensitive coherent-population-trapping (CPT) resonances are generated between the ground hyperfine levels on the D1{D}_{1}D1​ line of 133Cs^{133}\mathrm{Cs}133Cs using a two-photon $\mathrm{\ensuremath{\Lambda}}$ scheme excited by lin||lin polarizations. The frequency shift of the CPT resonance is 0.04 Hz for the deviation of $1\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{T}$ at a ``magic'' magnetic field of $139\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{T}$ and is 50 times smaller than that of the conventional clock transition at a typical bias magnetic field for the clock operation. The amplitude of the CPT spectrum excited by lin||lin polarizations is enhanced as the excitation intensity increases and is well explained by the three-level model without trap levels. Thus, the CPT resonance on the D1{D}_{1}D1​ line of 133Cs^{133}\mathrm{Cs}133Cs excited by a simple lin||lin scheme will be one of the best candidates for frequency reference of miniature atomic clocks.
The authors presented investigations on the application of CPT effect as alternative to the traditional optical microwave double resonance in small atomic clocks. An important factor which may limit the performances of CPT-based atomic clocks is the reduced signal contrast as compared to optical pumping. To overcome this limit, several excitation schemes have been proposed in the last years. Particularly, a significant enhancement of the CPT contrast can be obtained when co-propagating laser waves with parallel linear polarization (lin | | lin CPT) are resonant with the excited state Fe=l of alkali atoms.
We present a joint theoretical and experimental characterization of the coherent population trapping (CPT) resonance excited on the D1{D}_{1}D1​ line of 87Rb^{87}\mathrm{Rb}87Rb atoms by bichromatic linearly polarized laser light. We observe high-contrast transmission resonances (up to $\ensuremath{\approx}25%$), which makes this excitation scheme promising for miniature all-optical atomic clock applications. We also demonstrate cancellation of the first-order light shift by proper choice of the frequencies and relative intensities of the two laser-field components. Our theoretical predictions are in good agreement with the experimental results.
A scheme is studied for a coherent population trapping (CPT) atomic clock with counterpropagating left and right circularly polarized lasers, wherein the vertical-cavity surface-emitting laser and the partially reflecting mirror form an external cavity of an established length. With cancellation of spin-polarized dark states and interaction repeated with atoms, a CPT signal is obtained that is eight times larger than that of the conventional scheme. For the improvement of modulation efficiency, CPT resonance still can be excited with a lower microwave power compared with the conventional scheme. The experimental results suggest that it is an alternative for low-power atomic clocks.