The diffuser elements have {HEAD ~ an average space therebetween} of {TAIL ~ 50 to 300 micrometers} 
of
The diffuser elements have { HEAD ~ an average space therebetween } of { TAIL ~ 50 to 300 micrometers }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL