The mode behavior of symmetric air‐post vertical cavity surface emitting lasers is investigated using a unique tandem triple‐pass Fabry–Perot interferometer as well as standard characterization techniques. A series of high resolution spectra taken at various current levels demonstrates relaxation oscillations of the fundamental mode and the lifting of mode degeneracy by crystal birefringence and structural anisotropy. Near field images andL–Imeasurements identify the discontinuous jumps in mode number and polarization. ©1996 American Institute of Physics.