Experimental investigation of nonlinear coupling constant for circular polarizations in a spin-laser

The present study investigates experimentally the polarization dependence of the Lamb coupling constant C in a spin-VECSEL. A slight spatial separation of 20 µm is established between the two eigenmodes in the active medium, thereby artificially decreasing C to move away from the critical point C = 1. A robust simultaneous oscillation of the two eigenmodes is thus obtained, allowing accurate measurement C for both linear and circular polarizations. This experiment reveals a slight difference of coupling strength between linear polarizations, C = 1.19 ± 0.04, and circular polarizations, C = 0.97 ± 0.04.