Laser action in stellar envelopes

Model calculations for laser action in Hei are carried out, when helium plasma is rapidly cooled by expansion. Results are presented for four transitions, two of which, 3¹ S2¹ P ⁰ (7281) and 3¹ D2¹ P ⁰ (6678), show strong population inversion. Available observational evidence for possible laser action in these two lines in Wolf-Rayet and emission-line stars is summarized and discussed.