Defect recognition via longitudinal mode analysis of high power fundamental mode and broad area edge emitting laser diodes

A nondestructive method is presented which allows a precise detection of defects and their positions inside the cavity of semiconductor lasers. The defect recognition is based on the measurement of the longitudinal mode spectrum below threshold and the inspection of its Fourier transformation. Using a theoretical model, it is shown that a small distortion inside the cavity leads to a peak in the Fourier transformed spectrum from which the position of the distortion relative to the facets can be determined. For a ridge waveguide laser we find a direct correlation between defects identified by the analysis of the longitudinal mode spectrum and cathodoluminescence imaging. The applicability of this method for nondestructive defect recognition will also be demonstrated for broad area laser diodes with lateral multimode emission. The investigations reveal that the presented method can be used to assess the crystal quality of manufactured laser diodes.