Historical comments on the pumping of masers and lasers.

Provides historical comments on the pumping of masers and lasers. Research in the field of molecular microwave spectroscopy in the decade after World War II; Independent research efforts on the ammonia beam maser by Basov and Prokhorov; Masers and quantum electronics; Methods to obtain an inverted nuclear spin system; Optical pumping; Relevance of the multilevel pumping scheme.