Optimization of forward-scattered light energy and de-coherence of Mie scattering for speckle suppression

Abstract

Reducing the coherence of laser light without energy loss is critical for speckle suppression in laser projectors. In this paper, it is shown that more than 90 % of incident light is forward-scattered with complete de-coherence. We modeled a scattering volume with particles in ZEMAX as a scattering medium and studied the forward-scattered light energy and de-coherence dependence on the following three parameters: particle concentration, normalized radius of particles $$\upalpha $$ and refractive index ratio m. By varying all three parameters, a number of parameter combinations to achieve complete de-coherence are obtained, and which are utilized for speckle suppression. The forward-scattered light energy loss is up to 60–70 % of incident light at these combinations. But, at smaller particle concentration, the loss drops quickly. When setting the particle concentration at $$1\times 10^{8}\,\hbox {cm}^{-3}$$ , the forward-scattered light energy can be more than 90 % of incident light by adjusting $$\upalpha $$ and m according to Mie scattering theory. The structure parameter L of the scattering volume is also analyzed to collect forward-scattered light more than 90 % of incident light. These results can benefit the parameters’ choice of scattering particles and the design of a scattering volume used for speckle suppression.