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