A comprehensive study of the effects of different factors on anti-relaxation properties of octadecyltrichlorosilane-coated rubidium vapor cells

Anti-relaxation coatings play an important role in enhancing the polarization lifetime of polarized alkali-metal atoms. In this study, octadecyltrichlorosilane (OTS) was coated in spherical rubidium vapor cells fabricated using borosilicate glass with two stems as anti-relaxation coatings. An orthogonal experiment method was employed to obtain the optimal conditions. The results showed that OTS concentration is the dominant factor in the number of bounces, followed by the soaking time and molar ratio/(H2O:OTS). The optimal parameters were 6 mM of OTS, 6:1 of molar ratio/(H2O:OTS), and 80 min of soaking time. The number of bounces can be up to 200. Atomic force microscope images showed that the number and coverage ratio of clusters on the anti-relaxation coating fabricated by the optimized parameters are significantly less than the number and coverage ratio of clusters formed by other conditions. This means that the clusters in the coatings significantly affect the anti-relaxation performance. In addition, five OTS-coated cells were fabricated by A3B3C5 combination. However, the variability from cell to cell using the exact same preparation procedure can be up to 43.6%. The variability may be caused by the different aging times of the OTS solution. Because only one beaker of OTS solution was prepared, the OTS solution was pumped into the cells in sequence, not at the same time.