Optical frequency standards based on ultra-cold strontium atoms

As a key component of a strontium based optical clock, we have developed an apparatus which allows laser cooling and trapping of more than 10^{7 88}Sr atoms to temperatures below 1 μK. Using this system, we have performed the first high accuracy measurement of the ⁸⁸Sr ¹S₀-³P₁ clock transition using an ultra-cold sample. Detailed descriptions of both the measurement technique and corresponding systematic uncertainties is provided. In addition, by varying the density of the ultra-cold ⁸⁸Sr sample over a range of three orders of magnitude we obtain the first definitive measurement of a density-related frequency shift and linewidth broadening of an optical clock transition in an ultra-cold alkaline earth system. Spectroscopy of the ₁S₀-³P₀ transition is currently underway using this narrow probe laser and an octave spanning femtosecond laser. Our most recent results are presented. The proposed measurement technique, accuracy, and stability of an optical clock based on the EIT (electromagnetically-induced-transparency) measurement in ⁸⁸Sr are described.