a pinhole plate for receiving a first portion of {HEAD ~ the focused laser beam} through {TAIL ~ the pinholes} and, at the same time, reflecting a second portion of the focused laser beam back to the focusing lens 
through
a pinhole plate for receiving a first portion of { HEAD ~ the focused laser beam } through { TAIL ~ the pinholes } and , at the same time , reflecting a second portion of the focused laser beam back to the focusing lens
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH