▁the ▁rings ▁relate ▁to ▁the ▁sharp ▁edges ▁of ▁the ▁beam ▁created ▁by ▁the ▁edges ▁of ▁the ▁a pert ure . ▁This ▁pattern ▁is ▁called ▁an ▁Air y ▁pattern , ▁after ▁its ▁discover er ▁George ▁Air y . ▁ ▁By ▁alter ing ▁the ▁distribution ▁of ▁light ▁in ▁the ▁transform ▁plane ▁and ▁using ▁another ▁l ens ▁to ▁reform ▁the ▁col lim ated ▁beam , ▁the ▁structure ▁of ▁the ▁beam ▁can ▁be ▁alter ed . ▁The ▁most ▁common ▁way ▁of ▁doing ▁this ▁is ▁to ▁place ▁an ▁a pert ure ▁in ▁the ▁beam ▁that ▁allows ▁the ▁desired ▁light ▁to ▁pass , ▁while ▁blocking ▁light ▁that ▁corresponds ▁to ▁und es ired ▁structure ▁in ▁the ▁beam . ▁In ▁particular , ▁a ▁small ▁circular ▁a pert ure ▁or ▁" pin hole " ▁that ▁passes ▁only ▁the ▁central ▁bright ▁spot ▁can ▁remove ▁nearly ▁all ▁fine ▁structure ▁from ▁the ▁beam , ▁producing ▁a ▁smooth ▁trans verse ▁intensity ▁profile , ▁which ▁may ▁be ▁almost ▁a ▁perfect ▁g aussian ▁beam . ▁With ▁good ▁opt ics ▁and ▁a ▁very ▁small ▁pin hole , ▁one ▁could ▁even ▁approximate ▁a ▁plane ▁wave . ▁ ▁In ▁practice , ▁the ▁diameter ▁of ▁the ▁a pert ure ▁is ▁chosen ▁based ▁on ▁the ▁foc al ▁length ▁of ▁the ▁l ens , ▁the ▁diameter ▁and ▁quality ▁of ▁the ▁input ▁beam , ▁and ▁its ▁w avel ength ▁( long er ▁w avel ength s ▁require ▁larger ▁a pert ures ). ▁If ▁the ▁hole ▁is ▁too ▁small , ▁the ▁beam ▁quality ▁is ▁greatly ▁improved ▁but ▁the ▁power ▁is ▁greatly ▁reduced . ▁If ▁the ▁hole