Two-Color Grating Magneto-Optical Trap for Narrow-Line Laser Cooling

We demonstrate the two-color cooling and trapping of alkaline-earth atoms in a grating magneto-optical trap (GMOT). The trap is formed by a single incident laser beam together with four secondary beams that are generated via diffraction from a nanostructured wafer. A grating structure for a GMOT operating with strontium atoms is optimized and fabricated. We trap ${10}^{6}{\phantom{\rule{0.2em}{0ex}}}^{88}\mathrm{Sr}$ atoms on the ${}^{1}{S}_{0}{\ensuremath{\rightarrow}}^{1}{P}_{1}$ transition at $461\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$ and transfer 25% of these atoms to the second cooling stage on the narrower ${}^{1}{S}_{0}{\ensuremath{\rightarrow}}^{3}{P}_{1}$ intercombination transition at $689\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$, preparing a sample of $2.5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms at $5\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{K}$. These results demonstrate the applicability of the GMOT technology in conjunction with two widely differing wavelengths and enable the continued miniaturization of alkaline-earth-based quantum technologies like optical atomic clocks.