{HEAD ~ An optical element} may include a first diffractive structure having a radially symmetric amplitude function and a second diffractive structure having {TAIL ~ a phase function} 
{ HEAD ~ An optical element } may include a first diffractive structure having a radially symmetric amplitude function and a second diffractive structure having { TAIL ~ a phase function }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL