High-contrast nonlinear resonances in an $He-Ne/J_2$ ring laser

High-contrast nonlinear resonances were obtained for the first time in an $He-Ne/J_2$ laser with a ring resonator. Nine nonlinear resonances were observed, having a maximum contrast ratio of $\thicksim0,5$. It was found that the maximum contrast ratio of the resonances of a ring laser was almost independent of pressure.