Change in the absorption spectrum of potassium atoms under the action of resonant radiation

The broadening of $D$ lines and the two-photon absorption (TPA) line of 4S$_{1/2}\rightarrow$6S$_{1/2}$ potassium atoms due to the high-frequency Stark shift of excited levels in the field of intense monochromatic radiation (ruby laser) has been experimentally studied. . The broadenings were measured by the equivalent width method under conditions of an optically dense $k_0l\gg1$ layer. The dependence of the broadening on the pump intensity, which is quadratic for weak pumping, is revealed; it becomes linear at large intensity parameters. Estimates of the Stark shift of the 4P$_{1/2}$, 4P$_{3/2}$, 6S$_{1/2}$ levels and the broadening of $D$ lines and TPA lines of the potassium atom are given on the basis of experimental data.