Population inversion due to saturation of absorption in molecular rotation–vibrational transitions

A theoretical analysis is given of the attainment of population inversion by optical resonance pumping of the ground-state vibration under conditions ensuring equilibrium of the rotational sublevels. It is shown that the pumping of a single line makes it possible to achieve laser emission characterized by low energy losses (amounting to a rotational quantum) in a large number of rotation-vibrational lines, i.e., it is possible to emit simultaneously several laser frequencies. An analysis is made of the dependences of the absorption coefficients of the P, Q, and R lines on the number of the line resonant with the pumping radiation and on the value of the rotational constant. The absorption coefficient (gain) of the 1 → 0 transition of the HF molecule pumped on the P line region is calculated by way of example.