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IEEE Transactions on Instrumentation and Measurement

Observation of a Sub-10-Hz Linewidth $^{88}\hbox{Sr}^{+ \ \ 2}\hbox{S}_{1/2}$–$^{2}\hbox{D}_{5/2}$ Clock Transition at 674 nm

G. P. Barwood, Patrick Robert Gill, Guilong Huang, Hugh A. Klein

Published Mar 16, 2007• 21 citations
Publisher

Abstract

In this paper, a pair of diode lasers at 674 nm, locked to two independent ultralow-expansion high-finesse cavities, have been characterized by monitoring the beat frequency between them. The individual laser linewidth of 1.4 Hz for a 3-s averaging time broadened to 4 Hz at 30 s. The relative frequency stability of the beat at 1s is 2.5 10-15. One of the lasers has been used to interrogate the88Sr+2Si1/2-2D5/2transition at 674 nm, and a transition linewidth of 9 Hz has been observed

DOI
10.1109/tim.2007.891142

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Conference on Precision Electromagnetic Measurements•Dec 17, 2002•0 citations
Observation of a Sub-10-Hz Linewidth 88Sr+  2S1/2^{88}\hbox{Sr}^{+ \ \ 2}\hbox{S}_{1/2}88Sr+  2S1/2​–2D5/2^{2}\hbox{D}_{5/2}2D5/2​ Clock Transition at 674 nm
In this paper, a pair of diode lasers at 674 nm, locked to two independent ultralow-expansion high-finesse cavities, have been characterized by monitoring the beat frequency between them. The individual laser linewidth of 1.4 Hz for a 3-s averaging time broadened to 4 Hz at 30 s. The relative frequency stability of the beat at 1s is 2.5 10-15. One of the lasers has been used to interrogate the88Sr+2Si1/2-2D5/2transition at 674 nm, and a transition linewidth of 9 Hz has been observed
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.
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 clock laser based on a 30-cm-long ultrahigh finesse optical cavity was developed to improve the frequency stability of the Sr optical lattice clock at the National Institute of Metrology. Using this clock laser to probe the spin-polarized Sr87 atoms, a Rabi transition linewidth of 1.8 Hz was obtained with 500 ms interrogation time. Two independent digital servos are used to alternatively lock the clock laser to the S01 (mF=+9/2)→P03 (mF=+9/2) transition. The Allan deviation shows that the short-term frequency stability is better than 3.2×10−16 and averages down followed by 1.8×10−15/τ.
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
A prestabilized 674-nm diode laser has been narrowed by locking it to a high-finesse ultra-low-expansion cavity and kilohertz error signals have been observed. Lamb-Dicke confinement of single laser cooled Sr/sup +/ ions in a miniature rf trap has been demonstrated and micromotion reduction achieved. RF trap sidebands have been observed on the Sr/sup + 2/S/sub 1/2/-/sup 2/D/sub 5/2/ 674 mm clock transition. The transition frequency has been measured to be (444779043.98/spl plusmn/0.12) MHz (2/spl sigma/).