Imaging concentric modulations in transverse modes of a vertical-cavity surface emitting laser using a scanning near-field optical microscope

Concentric standing waves have been spatially imaged in the near-field regime within the optical aperture of a vertical-cavity surface emitting laser (VCSEL) using a scanning near-field optical microscope. Using the microscope's near-field collection mode and subsequent detection via a spectrometer it has been possible to design an experiment to determine the spatial location of multiple lasing modes in addition to concentric standing waves. At low injection current above threshold the standing waves influence and modulate the optical emission from multiple transverse modes. These results are discussed in relation to cavity and aperture effects, and pattern formation in VCSELs. Surface defects arising in the aperture are also seen to affect the optical output and are briefly discussed.