Calcium Cold-Atomic Beam Source

Cold Calcium Atomic Source, Clock Development Division, Precise Time Department The U.S. Naval Observatory (USNO) has a program to research and develop optical atomic clocks using a beam of calcium atoms. One of the biggest questions that needs to be answered is the potential gain in performance from using a beam of cold atoms, where laser cooling is used to reduce the center-of-mass velocity as well as the thermal distribution of velocities. Creating a beam of cold calcium atoms is accomplished using a hot oven followed by stages of longitudinal and transverse laser cooling. The laser cooling required is enabled by magnetic field gradients that tune the atomic frequency used in the cooling process. Recently, commercial products that produce cold atoms for applications have come to market. These range from an entire cold-atom system including vacuum chamber, optics, and lasers, to any of the sub-assemblies. The requirement is to procure a calcium atomic beam that provides the calcium oven, a longitudinal (Zeeman) slowing region, and regions for transverse cooling and deflection of the cold atomic beam. The system must be contained in a vacuum chamber that can be mounted to a USNO provided vacuum chamber for spectroscopy on the clock transition. This integration to the user-supplied chamber must be achievable without further conditioning of the vacuum in the provided beam chamber. Specifications: Calcium source (oven), loaded with a minimum of 5g of Ca. The oven must be able to heat Ca to >670C and run continuously at 600C or higher. The oven must be able to generate a flux corresponding to 100% absorption of resonant 423nm light across the atomic beam at 600C. The system must contain a region with a permanent magnet, longitudinal field Zeeman slower capable of generating velocities of 50m/s or lower with the oven at 500C, for 75mW of laser cooling light. There must be a heated window for the longitudinal slowing laser. The heating must prevent the window from becoming coated with calcium metal and allow it to maintain typical transmission at 423nm without degradation. The system must contain anti-reflection (for 423nm) coated windows and magnetic fields geometries to enable transverse cooling along two orthogonal to a temperature of ~3mK or lower for 30mW of cooling light. There must be a mechanism for separating slow atoms from fast, uncooled atoms and from longitudinal slowing laser. Gate valve or other mechanism allowing cold-atom vacuum system to be integrated to user-supplied vacuum chamber while cold-atom chamber is kept under vacuum. All vacuum components must be compatible with ultrahigh vacuum conditions, enabling pressures of order 1e-10 Torr. The integrated cold-atom source must be able to generate a flux of cold (~3mK transverse temperature, ~40m/s longitudinal velocity) atoms of 10^11 atoms/s or higher, out of a vacuum port that can integrate with a user-provided system. There must be transverse viewports with access to the hot atomic beam to allow 423nm spectroscopy for frequency stabilization of the cooling laser.