When I try to use TIRF illumination, I still have a lot of scattering light which generate sort of epi illumination as well. My set up includes high power laser, 10X beam expander, f=250mm achromatic doublet, four bands Semrock super-resolution laser filter set, 100X Olympus NA=1.5 objective. The alignment looks good (at least in the epi mode) and I can see the TIR beam returning through the objective.
I am not sure if this due to the 3 mm thickness of dichroic or not but I can see secondary scattered spots and a lot of interference patterns on the ceiling.
Also can anyone let me know the importance of circularly polarized light in TIRF microscope? Should I use it?