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Register a new userOptical frequency standard based on a two-photon transition in calcium
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Authors
Amar C. Vutha
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A two-photon transition in laser-cooled and trapped calcium atoms is proposed as the atomic reference in an optical frequency standard. An efficient scheme for interrogation of the frequency standard is described, and the sensitivity of the clock transition to systematic effects is estimated. Frequency standards based on this transition could lead to compact and portable devices that are capable of rapidly averaging down to $< 10^{-16}$.
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Extra-laboratory atomic clocks are necessary for a wide array of applications (e.g. satellite-based navigation and communication). Building upon existing vapor cell and laser technologies, we describe an optical atomic clock, designed around a simple and manufacturable architecture, that utilizes the 778~nm two-photon transition in rubidium and yields fractional frequency instabilities of $3times10^{-13}/sqrt{tau (s)}$ for $tau$ from 1~s to 10000~s. We present a complete stability budget for this system and explore the required conditions under which a fractional frequency instability of $1times 10^{-15}$ can be maintained on long timescales. We provide precise characterization of the leading sensitivities to external processes including magnetic fields and fluctuations of the vapor cell temperature and 778~nm laser power. The system is constructed primarily from commercially-available components, an attractive feature from the standpoint of commercialization and deployment of optical frequency standards.
The $5S_{1/2}rightarrow 5D_{5/2}$ two-photon transition in Rb is of interest for the development of a compact optical atomic clock. Here we present a rigorous calculation of the 778.1~nm ac-Stark shift ($2.30(4) times10^{-13}$(mW/mm$^2$)$^{-1}$) that is in good agreement with our measured value of $2.5(2) times10^{-13}$(mW/mm$^2$)$^{-1}$. We include a calculation of the temperature-dependent blackbody radiation shift, we predict that the clock could be operated either with zero net BBR shift ($T=495.9(27)$~K) or with zero first-order sensitivity ($T=368.1(14)$~K). Also described is the calculation of the dc-Stark shift of 5.5(1)$times 10^{-15}$/(V/cm$^2$) as well as clock sensitivities to optical alignment variations in both a cats eye and flat mirror retro-reflector. Finally, we characterize these Stark effects discussing mitigation techniques necessary to reduce final clock instabilities.
Two-photon resonance transition technology has been proven to have a wide range of applications,its limited by the available wavelength of commercial lasers.The application of optical comb technology with direct two-photon transition (DTPT) will not be restricted by cw lasers.This article will further theoretically analyze the dynamics effects of the DTPT process driven by optical frequency combs. In a three-level atomic system, the population of particles and the amount of momentum transfer on atoms are increased compared to that of the DTPT-free process. The 17% of population increasement in 6-level system of cesium atoms has verified that DTPT process has a robust enhancement on the effect of momentum transfer. It can be used to excite the DTPTs of rubidium and cesium simultaneously with the same mode-locked laser. And this technology has potential applications in cooling different atoms to obtain polar cold molecules, as well as high-precision spectroscopy measurement.
We have quantified a short term instability budget for an optical frequency standard based on cold, freely expanding calcium atoms. Such systems are the subject of renewed interest due to their high frequency stability and relative technical simplicity compared to trapped atom optical clocks. By filtering the clock laser light at 657 nm through a high finesse cavity, we observe a slight reduction in the optical Dick effect caused by aliased local oscillator noise. The ultimately limiting technical noise is measured using a technique that does not rely on a second clock or fs-comb.
Optical frequency standards, lasers stabilized to atomic or molecular transitions, are widely used in length metrology and laser ranging, provide a backbone for optical communications and lie at the heart of next-generation optical atomic clocks. Here we demonstrate a compact, low-power optical frequency standard based on the Doppler-free, two-photon transition in rubidium-87 at 778 nm implemented on a micro-optics breadboard. The optical standard achieves a fractional frequency stability of 2.9x10$^{-12}$/$sqrt{tau}$ for averaging times $tau$ less than 10$^{3}$ s, has a volume of $approx$35 cm$^3$ and operates on $approx$450 mW of electrical power. These results demonstrate a key step towards the development of compact optical clocks and the broad dissemination of SI-traceable wavelength references.
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