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Register a new userShelving spectroscopy of the strontium intercombination line
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Added by
Martin Robert-de-Saint-Vincent
Publication date
2019
fields
Physics
and research's language is
English
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We present a spectroscopy scheme for the 7-kHz-wide 689-nm intercombination line of strontium. We rely on shelving detection, where electrons are first excited to a metastable state by the spectroscopy laser before their state is probed using the broad transition at 461 nm. As in the similar setting of calcium beam clocks, this enhances dramatically the signal strength as compared to direct saturated fluorescence or absorption spectroscopy of the narrow line. We implement shelving spectroscopy both in directed atomic beams and hot vapor cells with isotropic atomic velocities. We measure a fractional frequency instability $sim 2 times 10^{-12}$ at 1 s limited by technical noise - about one order of magnitude above shot noise limitations for our experimental parameters. Our work illustrates the robustness and flexibility of a scheme that can be very easily implemented in the reference cells or ovens of most existing strontium experiments, and may find applications for low-complexity clocks.
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Using new experimental measurements of photoassociation resonances near the $^1mathrm{S}_0 rightarrow phantom{ }^3mathrm{P}_1$ intercombination transition in $^{84}$Sr and $^{86}$Sr, we present an updated study into the mass-scaling behavior of bosonic strontium dimers. A previous mass-scaling model [Borkowski et al., Phys. Rev. A 90, 032713 (2014)] was able to incorporate a large number of photoassociation resonances for $^{88}$Sr, but at the time only a handful of resonances close to the dissociation limit were known for $^{84}$Sr and $^{86}$Sr. In this work, we perform a more thorough measurement of $^{84}$Sr and $^{86}$Sr bound states, identifying multiple new resonances at deeper binding energies out to $E/h=-5$ GHz. We also identify several previously measured resonances that cannot be experimentally reproduced and provide alternative binding energies instead. With this improved spectrum, we develop a mass-scaled model that reproduces the observed binding energies of $^{86}$Sr and $^{88}$Sr to within 1 MHz. In order to accurately reproduce the deeper bound states, our model includes a second $1_u$ channel and more faithfully reproduces the depth of the potential. As determined by the previous mass-scaling study, $^{84}$Sr $0_u^+$ levels are strongly perturbed by the avoided crossing between the $^1mathrm{S}_0 + phantom{ }^3mathrm{P}_1$ $0_u^+$ $(^3Pi_u)$ and $^1mathrm{S}_0 + phantom{ }^1mathrm{D}_2$ $0_u^+$ $(^1Sigma_u^+)$ potential curves and therefore are not included in this mass-scaled model, but are accurately reproduced using an isotope-specific model with slightly different quantum defect parameters. In addition, the optical lengths of the $^{84}$Sr $0_u^+, u=-2$ to $ u=-5$ states are measured and compared to numerical estimates to characterize their use as optical Feshbach resonances.
We report the direct frequency measurement of the visible 5s$^2$ $^1$S$_0$-5s 5p$^3$P$_1$ intercombination line of strontium that is considered a possible candidate for a future optical frequency standard. The frequency of a cavity-stabilized laser is locked to the saturated fluorescence in a thermal Sr atomic beam and is measured with an optical-frequency comb-generator referenced to the SI second through a GPS signal. The $^{88}$Sr transition is measured to be at 434 829 121 311 (10) kHz. We measure also the $^{88}$Sr-$^{86}$Sr isotope shift to be 163 817.4 (0.2) kHz.
The high chemical reactivity of strontium, which can opacify a viewport exposed to a strontium atomic source, is a concern for some atomic physics experiments where it is sometimes necessary to send a laser beam counter-propagating relative to the atomic beam. While a number of experiments use heated sapphire windows to reduce strontium deposition and increase the viewport lifetime, here we study another possibility, consisting of sending the laser beam into the atomic flux by reflecting it off a mirror at 45$^{circ}$ exposed to the strontium flux. We present our attempt to find a substrate that can be exposed to strontium and maintain high reflectivity. We first present the formation of a strontium metallic mirror under high flux ($> 10^{13}$ at/s/cm$^2$) on a sapphire substrate, and measure its reflectivity at 45$^circ$ to be 0.65 (S) and 0.51 (P). On two other substrates, initially reflective metallic mirrors, we show for slightly lower fluxes (i.e., a factor of 3) that some reaction - most probably oxidation - is able to prevent the formation of the metallic layer even in high vacuum conditions. Instead, we observe the growth of a dielectric transparent medium. Despite the continuous deposition of strontium, the back surface reflectivity continues to dominate. We show the unusual evolution of reflectivity on these substrates, and emphasize two observations: i) a sharp threshold in the strontium flux separating transparent material growth from lossy material growth; ii) strontiums highly efficient capture of oxygen, even from rarefied sources: here mostly the residual high vacuum pressure (10$^{-7}$mbar full pressure) and possibly a protective SiO$_2$ surface on one of the substrates.
We present a combined experimental and theoretical study of the effects of Rydberg interactions on Autler-Townes spectra of ultracold gases of atomic strontium. Realizing two-photon Rydberg excitation via a long-lived triplet state allows us to probe the thus far unexplored regime where Rydberg state decay presents the dominant decoherence mechanism. The effects of Rydberg interactions are observed in shifts, asymmetries, and broadening of the measured atom-loss spectra. The experiment is analyzed within a one-body density matrix approach, accounting for interaction-induced level shifts and dephasing through nonlinear terms that approximately incorporate correlations due to the Rydberg blockade. This description yields good agreement with our experimental observations for short excitation times. For longer excitation times, the loss spectrum is altered qualitatively, suggesting additional dephasing mechanisms beyond the standard blockade mechanism based on pure van der Waals interactions.
The lifetimes and decay channels of ultralong-range Rydberg molecules created in a dense BEC are examined by monitoring the time evolution of the Rydberg population using field ionization. Studies of molecules with values of principal quantum number, $n$, in the range $n=49$ to $n=72$ that contain tens to hundreds of ground state atoms within the Rydberg electron orbit show that their presence leads to marked changes in the field ionization characteristics. The Rydberg molecules have lifetimes of $sim1-5,mu$s, their destruction being attributed to two main processes: formation of Sr$^+_2$ ions through associative ionization, and dissociation induced through $L$-changing collisions. The observed loss rates are consistent with a reaction model that emphasizes the interaction between the Rydberg core ion and its nearest neighbor ground-state atom. The measured lifetimes place strict limits on the time scales over which studies involving Rydberg species in cold, dense atomic gases can be undertaken and limit the coherence times for such measurements.
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