Evaporative Coating of Rb Maser Cells
نویسندگان
چکیده
The double-bulb rubidium maser (DBRM) relies on a vacuum cell for its operation. This differs from the spin-exchange noble gas cells which contain Xe, He and N2 as well as rubidium. These gases (in addition to playing active roles in the noble gas experiments) act as a buffer, keeping the Rb away from the walls of the cell. In the DBRM the lack of buffer gases allows rubidium atoms to effuse between the pumping and masing chambers of the device. Without a buffer gas, however, the device is very sensitive to rubidium-wall interactions which can shift the rubidium hyperfine frequency and even depolarize the atoms. Long polarization times may be obtained by coating the inner surface of the bulb containing the rubidium atoms with a benign substance. Previous work [2, 3] has shown that Rb bounces hundreds of times from a surface coated with tetracontane, C40H82, – a component of standard paraffin – (table 1), without losing its polarization (Fig. 1). Note in the figure that octadecyltrichlorosilane (OTS) [4], the coating used for noble gas cells is much less effective with rubidium. (Similar results have been found by other groups [5] after careful studies.) The tetracontane coating process is, however, somewhat complicated as the tetracontane must be evaporatively coated under vacuum. In the following sections of this document, we will describe the evaporative coating scheme as well as some of the details of Rb handling that may differ from the noble gas cells. We will also discuss the initial techniques used to characterize the coating quality as well as some earlier techniques used in coating DBRM cells.
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تاریخ انتشار 1999