Guido Saathoff

Precision spectroscopy of the 3s-3p fine-structure doublet in Mg+

We apply a recently demonstrated method for precision spectroscopy on strong transitions in trapped ions to measure both fine-structure components of the

Frequency Metrology on Single Trapped Ions in the Weak Binding Limit: The 3s1/2-3p3/2 Transition in 24Mg+

3s\text{\ensuremath{-}}3p

Comment on: “Lorentz violation in high-energy ions” by Santosh Devasia

transition in

M1/E2 decay rates in Co XI, Ni XII and Cu XIII measured at a heavy-ion storage ring

{^{24}\text{M}\text{g}}^{+}

The dynamics of bunched laser-cooled ion beams at relativistic energies

and

Sub-millikelvin spatial thermometry of a single Doppler-cooled ion in a Paul trap

{^{26}\text{M}\text{g}}^{+}

Combined Laser and Electron Cooling of Bunched C3+ Ion Beams at the Storage Ring ESR

. We deduce absolute frequency reference data for transition frequencies, isotope shifts, and fine-structure splittings that in particular are useful for comparison with quasar absorption spectra, which test possible space-time variations of the fine-structure constant. The measurement accuracy improves previous literature values, when existing, by more than two orders of magnitude.

Laser Cooling of Relativistic Heavy Ion Beams

We demonstrate a method for precision spectroscopy on trapped ions in the limit of unresolved motional sidebands. By sympathetic cooling of a chain of crystallized ions, we suppress adverse temperature variations induced by the spectroscopy laser that usually lead to a distorted line profile and obtain a Voigt profile with negligible distortions. We applied the method to measure the absolute frequency of the astrophysically relevant D2 transition in single 24Mg+ ions and find 1 072 082 934.33(16) MHz, a nearly 400-fold improvement over previous results. Further, we find the excited state lifetime to be 3.84(10) ns.

Photodissociation spectroscopy of OH+ molecular ions at the TSR storage ring

In an article ”Missing Transverse-Doppler Effect in Time-Dilation Experiments with High-Speed Ions” by S. Devasia [arXiv:1003.2970v1], our recent Doppler shift experiments on fast ion beams are reanalyzed. Contrary to our analysis, Devasia concludes that our results provide an ”indication of Lorentz violation”. We argue that this conclusion is based on a fundamental misunderstanding of our experimental scheme and reiterate that our results are in excellent agreement with Special Relativity. We have performed experiments of the Ives-Stilwell (IS) type [1] that test time dilation of Special Relativity (SR) via the relativistic Doppler shift [2,3,4,5]. A beam of ions, which exhibit an optical transition with a frequency ν0 in their rest frame, is stored at velocity β = v/c in a storage ring. To resonantly excite these ions by a laser at rest in the laboratory frame, the frequency ν of the laser needs to be Doppler shifted according to ν = ν0/γ(1 − β cos θ), where θ is the angle between the laser and the ion beam, measured in the laboratory frame, and γ governs time dilation. For a parallel (θp = 0) or an antiparallel (θa = π) laser beam the frequencies required are νp,a = ν0/γ(1 ∓ β), respectively. Multiplying these two frequencies and using γ = (1 − β) as predicted by SR results in νpνa/ν 2 0 = 1, (1) i.e. the geometric mean of the Doppler shifted frequencies equals the rest frame frequency for all velocities β. In one of our implementations of the IS experiment saturation spectroscopy is used by overlapping simultaneously a parallel and antiparallel laser beam with the ion beam to select a narrow velocity class β0 within the ions’ velocity distribution. The parallel laser is held fixed at the laser frequency νp = ν0/γ(1 − β0) and is resonant with ions at β0, while the other laser is scanned over the velocity distribution. The fluorescence yield, measured with a photomultiplier (PMT) located around 90 degree with respect to the ion beam, will exhibit a minimum (a Lamb dip) when the antiparallel laser talks to the same velocity class β0, i.e. when its frequency is at νa = ν0/γ(1 + β0). SR thus predicts the Lamb dip to occur when Eq. 1 is fulfilled, which is shown to be confirmed by our experiments to an accuracy of < 2 × 10 on Li ions at β0 = 0.03 and β0 = 0.06 [3]. S. Devasia [6] claims that the Doppler shift of the emitted light has to be taken into account and replaces ν0 in Eq. 1 by γν0, i.e. by the frequency of the light detected exactly at θ = π/2. This is a misconception of our experimental measurement scheme. While it is true that the detected light is Doppler-shifted, this Doppler shift is irrelevant for the analysis. Neither do we measure the frequency ν0 β 0 PMT ν a =ν 0 /γ(1+β 0 ) IF ν p =ν 0 /γ(1−β 0 ) of the emitted light nor do we intend to observe at exactly right angle. We only record the number of re-emitted photons as a function of the scanning laser frequency to monitor the Lamb dip caused by the simultaneous resonance of both lasers with the same ions. Thus the angle of detection is irrelevant but θ ≈ π/2 helps to separate fluorescence from laser stray light. In fact, stray light suppression is the only reason for using an interference filter (IF) in front of the PMT; its transmission width of 10 nm corresponds to 10 THz, about 10 times broader than the width of the Lamb dip, and a factor of 10 larger than the transverse Doppler shift (at β = 0.064). None of the filters employed in our experiments [2,3,4,5] to improve the signal-to-noise ratio in the fluorescence light detection are affecting the shape and position of the signal indicating the resonance of the parallel and antiparallel laser with the same velocity class β0. The frequency ν0 occurring in Eq. 1 has nothing to do with the frequency of the emitted light in our experiment, but is the rest frame frequency ν0 deduced from experiments at smaller ion velocities [3,7]. In conclusion, SR predicts Eq. 1 as the outcome of our experiments, which is confirmed with high accuracy.

Preparatory measurements for a test of time dilation in the ESR

Rates of the electric-dipole forbidden transition in the ground configuration of Cl-like ions of Co, Ni and Cu have been measured optically at a heavy-ion storage ring. Besides testing theory and providing benchmark data for these ions, the data by isoelectronic extrapolation pertain to the Fe X spectrum of high solar interest, for which so far theory and experiment have disagreed.