Hi,
I am modelling a setup in which an LED light source is homogenized using two fly's eye multi-lens arrays.
There exists already a tutorial on a fly's eye setup:
In my setup, I have chosen components that are all off-the-shelf available.
My setup consists of:
1. LED light source, wavelength = 340 nm, emitter size = 6x6 mm.
2. Collimating lens, spherical type, focal length = ~50 mm @340 nm.
3. MLA1: a multi-lens array with pitch = 7 mm (in 
and 5.4 mm (in Y) and nr of lenslets in X = 7 and in y = 9 and focal length ~ 40 mm at 340 nm.
4. MLA2: identical to MLA1. MLA2 is placed in the focal length of the MLA, that is at 40 mm behind MLA1. This is the classical fly's eye setup configuration.
5. A focusing lens with f = 474 mm @340 nm.
What I observe:
1. A square-like top-hat profile at the focal plane of the focusing lens (see figure in additional post below).
2. A cross-like pattern on top of the top-hat profile.
Question:
1. What could cause the cross-like pattern on top of the top-hat profile? The LED source is collimated by the collimating lens. Any suggestions to keep me going on a next step, is highly appreciated.
Pattern just before MLA2: it shows the individual beamlets.
