The National Research Council of Canada (NRC) is currently involved in a number of research projects aimed
at improving time and frequency realization based on the accurate and precise stabilization of microwave and
optical sources on atomic and molecular transitions. Projects described in this summary will focus on the
development of a primary standard for the realization of the SI second based on a cesium atomic fountain and
a next generation standard based on an optical transition in a single trapped and laser cooled ion of strontium.
The cesium fountain is undergoing evaluations of its systematic shifts for an eventual contribution to TAI and
for a re-measurement of the absolute frequency of the strontium ion clock transition at the 10-15 level. The
main contribution to the uncertainty budget of the fountain is thought to be caused by the inhomogeneity in the
magnitude of the magnetic field in the drift region. The latest measurements of this field are presented. A new
strontium ion trap of the endcap design was completed last year. This new system has compensation electrodes
and access ports in three orthogonal directions to control the ion position and minimize micromotion. We report
preliminary results indicating improved performance of this trap over our previous rf Paul trap. As part of an
effort to reduce the systematics shifts to a minimum, the heights of the atomic standards above the geoid were
measured with an accuracy of 5 cm, corresponding to a fractional frequency uncertainty of 5 × 10-18 for the
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 5s2S1/2-4d2D5/2 (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+.
A 445-THz (674nm), 88Sr+ trapped and laser cooled single ion reference transition has been used at the National Research Council of Canada (NRC) to extend precision frequency measurements to other points in the electromagnetic (EM) spectrum. We are currently refining the single ion experiment to approach the uncertainty limited spectral resolution of 1×10-15. Connected with these developments is the use of frequency grids based on mode-locked femtosecond lasers. A band of reference modes extending from 520 nm to beyond 1060 nm has been recently obtained femtosecond lasers. A band of reference modes extending from 520 nm to beyond 1060 nm has been recently obtained at NRC and has been applied to the absolute frequency measurement of the widely used 633 nm I2 stabilized HeNe laser standard. Excellent agreement was obtained between the measurements determiend via ion an comb based measurements. With such devices, the possibility of accurate, stable and compact sources at any wavelength is coming into being.
A single ion, trapped, laser cooled and probed on an ultra- narrow transition, provides what is widely considered the best approximation to an ideal, isolated optical frequency reference. Our group has been actively studying the 445-THz (674 nm), 5s2S1/2-4d2D5/2 transition in 88Sr+. Individual Zeeman component linewidths of 250 Hz were observed and a probe laser system was locked to the center frequency of the Zeeman spectrum. A cesium-based frequency chain was used to measure the center frequency of the 88Sr+ S-D spectrum to an accuracy of 200 Hz. Under our current experimental conditions, the magnitudes of the systematic shifts in the linecenter position are estimated to be less than 1 part in 1015. As part of our efforts in improving the trapped ion standard, we have studied the coherent excitation of a single ion via Rabi pulse and Ramsey fringe interrogation. Initial results yielding Ramsey fringe widths down to 840 Hz were obtained, and some decoherence and motional properties of the ion system were investigated. The Sr+ standard was applied recently to the well-known He- Ne/I2 standard at 633 nm. This measurement provided an accuracy comparison between a traditional frequency chain and a femtosecond laser frequency comb. In addition, after several months and transportation over a significant portion of the globe, 88Sr+ calibrated 633 nm lasers from NRC and BIPM have shown agreement to 1 kHz in their originally determined absolute optical frequencies. The results of these intercomparisons point to potential worldwide accuracy improvement of working 633 nm radiation standards.