A spectroscopically-resolved photoluminescence microscopy technique for the optical study of semiconductor laser diodes is described. The system has been developed by incorporating a twin etalon tuneable filter with a spectral width of 0.6 nm into an existing photoluminescence microscopy imaging system. The design calculations used to make the experimental apparatus are compared with results from the developed system and show reasonable agreement. The study of packaging-induced strain and defects in high-power laser diodes is used to illustrate this technique. Initial results are presented and compare well with an existing technique, micro-photoluminescence spectroscopy. The results show that shifts (< 1 nm) in the peak photoluminescence wavelength can be observed in regions with defects and/or different soldering-induced strain. Luminescence shifts as large as 15 nm in the region around a dark line defect are observed and these cause a significant disturbance in the strain field in the adjacent regions, where luminescence shifts as large as 5 nm are observed.