The grating can have {TAIL ~ a periodicity} from 200 nm to {HEAD ~ 500 nm} 
The grating can have { TAIL ~ a periodicity } from 200 nm to { HEAD ~ 500 nm }
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD