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