Theoretical analysis of the hollow beam geometry for dynamic light scattering

Hollow beam geometry in conjunction with mode-selective detection allows to realize high-sensitivity apparatuses for quasi back-scattering measurements. I present a complete theoretical analysis of the hollow beam geometry recently proposed for dynamic light scattering measurements in the human eye. The aim of the analysis is to determine the excitation and observation beam profiles at the focal plane, the volume under test and the pre-detection signal. In the analysis the concept of characteristic length of a scattering system is introduced. Using a simple formula, this parameter allows the calculation of the collection efficiency for a general beam shaping. Moreover it is extremely useful to compare the performance of different systems.