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