The method may further include filling {HEAD ~ a space} between {TAIL ~ the first optical window} and the second optical window with a filler 
between
The method may further include filling { HEAD ~ a space } between { TAIL ~ the first optical window } and the second optical window with a filler
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH