Near-Field Scanning Optical Microscopy Measures Diode Beam Properties

Astigmatism is a problem for laser diodes, and even after applying correctional optics, residual astigmatism (a few microns) remains because of laser-to-laser variations. In addition, temperature and pump current variations may affect astigmatism and other beam properties. Knife-edge techniques with mathematical processing can produce reasonably accurate assessments of beam parameters, but researchers at Boston University and the IBM Research Center in Switzerland wrote in Applied Physics Letters that they can produce very high resolution direct lateral and axial diode laser beam profile and astigmatism measurements using near-field scanning optical microscopy. The group used the near-field tip to collect an InGaAs diode output at various heights above the facet.