These flame-sealed cells contain a small amount of solid, >98% chemically pure, isotopically pure rubidium 85 (⁸⁵Rb) under vacuum. The concentration of rubidium in the vapor phase may be controlled by heating the cell or cooling the tipoff stem. Operating temperatures typically range from 20-80°C. Rubidium has intermitant strong absorption lines which are used for calibration of tunable lasers and wavelength meters in the range of 6540-48300 cm^-1 (207-1529 nm). They may also be used to stabilize laser frequencies via locking to a single strong absorption line.

The quartz cell body is cylindrical in shape; outer diameter 19 mm; length 75 mm. The tipoff stem is centered on the cell, protruding not more than 10 mm from the cell body. Windows are angled 11° off of normal and have a 2° interior wedge to prevent back-reflection and etalon effects.