Observation of wave front curvature inside a vertical‐cavity surface‐emitting laser

By performing interferometric measurements on the fundamental transverse mode of a planar VCSEL, we have determined the wave front curvature inside the VCSEL cavity. The results show that the (apparent) position of the beam waist is 0–8 μm below the surface of the top DBR, i.e., up to 25% of the Rayleigh range. From these results we estimate the amount of index and gain guiding in the VCSEL.