Classification (contd...)

The variation of the radiation intensity after scattering as a function of the particle diameter-to-wavelength ratio is shown schematically in Figure 7.1. The regimes of geometric, wave, and quantum optics are highlighted. It is intrinsically true that signal strengths in the quantum domain are weaker than in wave domain, that in turn are smaller than in geometric optics. This expectation is borne out in Figure 7.1. Geometric optics has been discussed at length in the module on particle image velocimetry. The present module is focused on wave and quantum domain measurements of flow properties using the scattering phenomenon.

Figure 7.1: Intensity of the scattered radiation plotted as a function of the particle diameter-to-wavelength . Rayleigh scattering is at the interface between wave and quantum optics at . Geometric optics is predominant for the ratio greater than around 25.