Investigation of ruby single crystals intended for use in a 4-cm traveling-wave symmetrically pumped maser

An analysis was made of the problem of pumping of traveling-wave ruby masers emitting in the range 3.5–5 cm. Tests were made on ruby single crystals grown by the Verneuil method in various establishments and also on those prepared by a special technology developed at the State Optical Institute (SOI). These crystals were used as active materials in traveling-wave symmetrically pumped masers. An ESR spectrometer with frequency scanning operating at 4.2 °K was developed. It was found that the ruby crystals grown using the SOI technology had the minimum block structure and could be used successfully in traveling-wave symmetrically pumped masers right up to the limit of emission λ≈5.2 cm.