Rotational relaxations in a high pressure N2 laser

While with N2 gas alone the number of rotational lines in a laser plasma cavity decreases with increasing gas pressure (beyond 300 torr), a mixture of N2 and Ar yields a significant decrease in the intensities of the P3 branch lines as compared with the P1 and P2 branch lines. When the partial pressure of Ar is greater than that of N2, the P3 branch lines are completely absent, but appear if the N2 partial pressure is greater than that of Ar. At the same total pressure of the gas, the rotational lines are sharper in a mixture of N2 and Ar than in N2 alone.