Versatile Rb vapor cells with long lifetimes

The authors report on an approach to the construction of long-lasting rubidium atomic vapor cells. The method uses pinch-off copper cold-welds, low temperature solders, and electroplated copper to create long-lasting hermetic seals between containment chambers of dissimilar geometries and materials. High temperature epoxy, eutectic lead/tin solder, and indium solder were considered as sealing materials. These seals were analyzed using accelerated lifetime testing techniques. Vapor cells with epoxy and bare metal solder seals had a decrease in the rubidium atomic density within days after being heated to elevated temperatures. They also exhibited broadened spectra as a result of rubidium reacting with the seals. However, indium solder seals with a passivation coating of electroplated copper did not exhibit a significant decrease in linewidth or atomic density after being held at 95 °C for 30 days. The authors conclude that this particular seal has no rubidium chemical reaction failure mode and when used in combination with copper cold welding has the potential to create multiplatform vapor cells with extremely long lifetimes.