ABSTRACT
The propagation behaviour of a highly coherent laser beam can be predicted from a detailed knowledge of both the power/energy density distribution and the relative phase distribution in a single transverse plane of the beam. Complete characterization of a more general beam requires knowledge of the mutual coherence function combined with complex measurement and analysis procedures. A much simpler and equally useful procedure that can be used to predict much of the propagation behaviour of laser beams, as well as some incoherent broadband beams of light, involves measurement of the beam diameter and divergence. The measurements are made using second-order moment analysis of the transverse power/energy density distribution at a number of positions along a beam. This section of the handbook is devoted to describing this latter technique. In what follows, the word ‘irradiance’ is used to mean the power/energy density in a transverse plane of a beam.
