Such hierarchical embodiments enable {HEAD ~ the use} of {TAIL ~ larger collector optics} than single stage embodiments of the present invention 
Such hierarchical embodiments enable { HEAD ~ the use } of { TAIL ~ larger collector optics } than single stage embodiments of the present invention
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH