Further, {HEAD ~ even the conventional techniques} for generating approximate Bessel beams are associated with {TAIL ~ difficulties} in optical techniques 
Further , { HEAD ~ even the conventional techniques } for generating approximate Bessel beams are associated with { TAIL ~ difficulties } in optical techniques
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH