In particular, Bessel beams are light beams having properties most similar to those of LG beams, however, {HEAD ~ currently known generating techniques} can only generate {TAIL ~ approximate Bessel beams} 
In particular , Bessel beams are light beams having properties most similar to those of LG beams , however , { HEAD ~ currently known generating techniques } can only generate { TAIL ~ approximate Bessel beams }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL