Study of parameters of simultaneous lasing on two lines sharing an upper level

Stationary lasing at two competing lines sharing an upper level is studied. Based on the expressions for the gain obtained earlier, the possible lasing regimes are considered (at one or two lines) and approximate formulas are derived for determining the output power in each line. These formulas are shown to be the generalisation of the Rigrod formula to the case of simultaneous lasing at several lines.