De-excitation in Electronic Collision Process in Gas Lasers

The laser action produces changes of population in the upper and lower levels involved. These population changes lead to the light intensity changes of spontaneous emission originating from the upper and lower levels, Δ I 52 and Δ I 21 , respectively. The ratio of these intensity changes, Δ I 21 / Δ I 52 , is theoretically calculated. By analysing the experimental data of this ratio observed on 6328Å emission in a He-Ne laser, the probabilities of de-excitation by electronic collision of the upper 3 s 2 and lower 2 p 4 levels, P 52 e and P 21 e , respectively, are obtained. The value of probability P 52 e at a discharge current of 30 mA for a laser tube of 3.5 mm diameter is (3.4±0.6) × 10 7 sec -1 and is of the same order as the total probability of radiative transition of 3 s 2 level, A 52 . The total cross section of this electronic collision process σ 52 e is estimated to be (6.8±1.2) × 10 -13 cm 2 . The value of P 21 e at 30 mA is much smaller than the value of the probability of 2p 4 level, A 21 . This technique also yeilds the ratio of A 52 / A 521 to be 2.1±0.8, where A 521 is the probability of radiative transition from 3s 2 level to 2p 4 level.