Under pumping spot size less than that of the cavity mode, we observed a decrease of the fundamental mode power in an end-pumped solid-state laser when the cavity length was adjusted approaching certain critical resonator configurations where the transverse modes are degenerate. In the proximity of these configurations, we found, for the first time to our knowledge, that the laser exhibits a relatively low threshold pump power together with an unexpected far-field beam profile and shrinking beam waist.
