Stimulated Laser Cooling in a Compact Geometry Using Microfabricated Atomic Beam Collimators

We have developed a compact and highly efficient assembly for stimulated laser cooling of thermal rubidium atomic beams traveling upon planar silicon devices. Following precollimation via a silicon microchannel array, we perform beam brightening via a blue-detuned optical molasses [Aspect et al., Phys. Rev. Lett. 57, 1688 (1986)]. Owing to the small size of the chip elements, we require only 8 mW to implement the efficient cooling scheme, making it well suited for future portable atomic sensors that require minimal size, weight, and power consumption. Small mirrors are fabricated and hand-assembled to precisely overlap a strong elliptical standing wave with a sheet-shaped atomic density distribution, with dimensions chosen precisely to match these. We reduce the transverse velocity spread to below 1 m/s within an interaction length of 4.5 mm above the silicon substrate. We use Doppler-sensitive two-photon Raman spectroscopy to characterize the cooling. In contrast to time-of-flight methods utilized previously, this approach requires a much shorter apparatus to achieve similar resolution. This hybrid of passive and active collimation paves the way toward the construction of fully fledged atomic instruments, such as atomic beam clocks and gyroscopes, entirely on-chip through batch-fabricated processes.