Assembly for separating radiation in the far field

An assembly for separating first radiation and second radiation in the far field, wherein the first radiation and the second radiation have non-overlapping wavelengths, the assembly comprising:

• a capillary structure, wherein the first radiation and the second radiation propagate coaxially along at least a portion of the capillary structure and an optical axis of the second radiation;
• and
• an optical structure configured to control a spatial distribution of the first radiation outside of the capillary structure, through interference or diffraction, such that an intensity of the first radiation in the far field is reduced along the optical axis and is substantially separated from the second radiation in the far field while the second radiation continues to propagate along the optical axis.