Figure 1. Setup for studying statistics of partially-developed speckle and caustics.

An SLM encodes random spatial phase on a coherent beam from a He-Ne laser. Free space propagation transforms this random phase to random intensity fluctuations. An imaging system is used to reduce the size of the beam so it can be recorded on a CCD camera which can be translated longitudinally over an extended measurement volume. All measurement distances given in the text are relative to the origin z = 0 of the axes shown. Here f₁ = 500 mm, f₂ = 250 mm, f₃ = 100 mm, f₄ = 9 mm.