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Conference on Precision Electromagnetic Measurements

Measurement of the 88Sr+ reference transition frequency with a new probe laser system

P. Dubé, L. Marmet, Alan A. Madej, J. E. Bernard

Published Jun 1, 2004• 4 citations
Publisher

Abstract

The authors have designed and implemented a new 674 nm (445 THz) laser system for probing the ultranarrow 5s2S1/2-4d2D5/2reference (clock) transition of the trapped and laser-cooled88Sr+ion. The authors describe briefly the double-stage probe laser system; linewidths of (50 plusmn 9) Hz FWHM were observed for the clock transition with this source. Results on the determination of the temperature of zero thermal expansion coefficient of the reference cavity were also presented. Preliminary measurement of the absolute frequency of the88Sr+clock transition frequency gives a frequency of (444779044095472 plusmn 15) Hz

DOI
10.1109/cpem.2004.305574

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We are studying a single Sr/sup +/ atom confined in a Paul trap to produce a frequency standard in the visible region of the spectrum. The goal is to excite a clock transition of the ion at 674 nm with a diode laser and measure its absolute frequency. It is only possible to probe the 0.3-Hz transition if the diode laser is extremely stable during the measurement process which in this experiment can take several minutes to complete. Frequency stabilization of the probing laser was achieved with a lock to an ultra-stable Fabry-Perot cavity. The cavity was temperature stabilized and has demonstrated good long term stability.

Conference on Precision Electromagnetic Measurements•Dec 23, 2002•0 citations
The authors have designed and implemented a new 674 nm (445 THz) laser system for probing the ultranarrow 5s2S1/2-4d2D5/2reference (clock) transition of the trapped and laser-cooled88Sr+ion. The authors describe briefly the double-stage probe laser system; linewidths of (50 plusmn 9) Hz FWHM were observed for the clock transition with this source. Results on the determination of the temperature of zero thermal expansion coefficient of the reference cavity were also presented. Preliminary measurement of the absolute frequency of the88Sr+clock transition frequency gives a frequency of (444779044095472 plusmn 15) Hz
The present decade has seen great advances in optical frequency standards following the development of femtosecond laser frequency combs. With this technology, combined with a stable and narrow probe laser source (50-100 Hz linewidth), we made a systematic study of the 5s 2S1/2-4d 2D5/2 (S-D) transition frequency of the 88Sr+ ion as a function of the quantization axis in the trap. This study revealed the presence of systematic shifts caused by residual micromotion in our rf Paul trap and led to an evaluation of those shifts. Also, a method was developed based on the measurement of the Zeeman spectrum of the clock transition to cancel the electric quadrupole shift caused by patch potentials on the trap electrodes. From these results, we also determined the absolute frequency of the S-D clock transition frequency at 674 nm with a fractional frequency uncertainty of 3.4 × 10-14. We have since made improvements to our probe laser system and have observed 5 Hz Fourier transform limited linewidths on a Zeeman component of the S-D transition of the 88Sr+ ion. To observe such a narrow transition it is essential to have a known and well behaved drift of the laser frequency during the few minutes it takes to measure the ion resonance using the quantum jump signal. Our approach to minimize the drift rate and its sensitivity to temperature fluctuations has been to stabilize the cavity at the temperature where its coefficient of thermal expansion is zero. We will present an overview of our recent progress made on the frequency standard based on the laser-cooled and trapped single ion of 88Sr+.
An optical frequency standard, based on the 674 nm 2S1/2-2D5/2 'clock' transition in a laser cooled trapped strontium ion is currently being evaluated at the UK National Physical Laboratory. The probe laser is a narrowed AlGaInP diode laser locked to a highly-stable and ultra-low- expansion high-finesse cavity. Laser linewidths of less than 200 Hz have been observed, measured by scanning over a single Zeeman component at 674 nm. The development of this laser is described, together with factors currently limiting the observed linewidth. Three 88Sr+ traps are now in operation, and the probe laser source can be simultaneously locked to the center of the 2S1/2 - 2D5/2 Zeeman multiplet in any two of the three traps, allowing a comparison between them. Recent results on this comparison are presented.
A simultaneous observation of the optical-clock ${}^{2}{S}_{1/2}{\ensuremath{-}}^{2}{D}_{5/2}$ transition at 674 nm, in two separately trapped single 88Sr+{}^{88}{\mathrm{Sr}}^{+}88Sr+ ions, is reported. Two nominally identical miniature rf Paul traps were used together with a 674-nm sideband-injection-locked extended-cavity diode laser. This ``slave'' laser was optically phase locked about 650 MHz away from a ``master'' diode laser, which was itself locked to a high-finesse, ultra-low-expansion (ULE) cavity. The ULE cavity was temperature-stabilized and suspended in an evacuated enclosure, and provided an ``optical flywheel'' reference standard with a relative drift rate of better than 1 part in 1011{10}^{11}1011 per hour. The difference between center frequencies of the single 88Sr+{}^{88}{\mathrm{Sr}}^{+}88Sr+-ion 674-nm (445-THz) transition multiplet in two traps was 120(90) Hz (one standard uncertainty). Thus the two trap center frequencies agree to 3 parts in 1013.{10}^{13}.1013.
We report on an improved absolute frequency measurement of the 5s 2 1 S 00-5s5p 3 P 0 narrowline clock transition at 236.5 nm, for a single, trapped, and laser-cooled 115In ion. Using a narrowline laser as the local oscillator, a linewidth of 43 Hz for the transition is resolved. The uncertainty of the transition frequency’s centroid is 18 Hz, leading to a fractional uncertainty of 1.4 × 10−14. For absolute frequency measurement, we use an optical frequency comb locked to a cesium clock as the reference. The transition frequency is found to be 1267402452900967(63) Hz, averaged over 13 days of separate measurements. The accuracy is about 5.0 × 10−14. We discuss possibilities for further improvement.
The electric quadrupole shift is an important source of systematic uncertainty in several single-ion optical frequency standards. In this paper, we review the electric quadrupole shift cancellation method based on the Zeeman spectrum of the clock transition. The method is demonstrated with an actual frequency measurement of the 5s2S1/2-4d2D5/2transition of88Sr+. This cancellation method also removes shifts from the tensor part of the Stark effect. Further analysis of the data provides an evaluation of the micromotion shifts which are then applied to correct the observed ion clock frequency. Recent improvements to our probe laser system and the observation of Fourier-transform limited linewidths of 5 Hz at 445 THz are also reported
We are studying a single Sr/sup +/ atom confined in a Paul trap to produce a frequency standard in the visible region of the spectrum. The goal is to excite a clock transition of the ion at 674 nm with a diode laser and measure its absolute frequency. It is only possible to probe the 0.3-Hz transition if the diode laser is extremely stable during the measurement process which in this experiment can take several minutes to complete. Frequency stabilization of the probing laser was achieved with a lock to an ultra-stable Fabry-Perot cavity. The cavity was temperature stabilized and has demonstrated good long term stability.