Abstract
Temperatures below the Doppler limit of $1.9\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ have been observed in magnesium. The strong cooling transition was modified by a coherent two-color excitation exploiting the longer lifetime of an upper level. We developed a theoretical model to describe the light forces and cooling originating from the induced quantum interference in a three-level system. Time-of-flight measurements verified temperatures of $500\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ in a one-dimensional (1D) molasses in accordance with our theoretical model. By implementing this scheme in a 3D magneto-optical trap with a single ir beam, temperatures as low as $1\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ could be realized. For ideal conditions we extrapolate to temperatures of $50\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$. With cooling times of about $1\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$, a fast and efficient cooling scheme was realized, particularly attractive for optical frequency standards.
Published Version
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