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