These flame-sealed cells contain a small amount of solid, >98% pure potassium (K) under vacuum. The concentration of potassium in the vapor phase may be controlled by heating the cell or cooling the tipoff stem. Operating temperatures typically range from 20-50°C. Potassium has intermitant strong absorption lines which are used for calibration of tunable lasers and wavelength meters in the range of 2490-45660 cm^-1 (219-4016 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.