the diffuser elements have an average space therebetween of {TAIL ~ 50 μm} to {HEAD ~ 300 μm}, 
the diffuser elements have an average space therebetween of { TAIL ~ 50 μm } to { HEAD ~ 300 μm } ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH