Beam divergence and waist measurements of laser diodes by near- eld scanning optical microscopy

We demonstrate the use of neareld scanning optical microscopy (NSOM) for the measurement of the beam properties of SQW-GRINSCH ridge laser diodes. Using NSOM, we measure the eld intensity in the transverse plane at neareld and as a function distance from the facet. The divergence of the laser beam and the beam waists in vertical and lateral dimensions are directly measured and the astigmatism of the mode is determined. In the neareld we observe a nearly ideal Gaussian shape in the vertical dimension (along the crystal growth) which is consistent with the beam divergence as measured in the fareld. In the lateral dimension, the beam shape deviates from the ideal Gaussian since the mesa structure of the laser diode provides an e ective step-index waveguide. The non-Gaussian structure of the mode is also observed in the beam divergence properties.