突破衍射极限的成像方法综述

龙源期刊网突破衍射极限的成像方法综述作者：乌拉郑玉祥来源：《光学仪器》2017年第01期摘要：“衍射极限”实际上不是一个真正的障碍，除非处理远场和定位精度。这种衍射障碍并不是坚不可摧的，可以利用一些智能技术来突破光学衍射极限。讨论了四种技术，近场扫描光学显微镜（NSOM）法，受激发射损耗（STED）显微镜法，光激活定位显微镜（PALM）法或随机光学重建显微镜（STORM）法和结构照明显微镜（SIM）法，并且介绍了各自的基本原则与优劣。NSOM利用纳米级探测器检测通过光纤的极小汇聚光斑，从而获得单个像素的分辨率；PALM和STORM利用荧光探针，实现暗场和荧光的转换，从而观察到极小的荧光团；SIM则是利用栅格图案与样品叠加成像来实现。其中，STORM具有相对较高的潜力，能够更为有效地突破衍射极限。关键词：衍射极限；近场显微镜；三维显微中图分类号：O43文献标志码：Adoi：10.3969/j.issn.10055630.2017.01.014AreviewonimagingmethodstobreakthediffractionlimitRamzanUllah1，2，ZHENGYuxiang1（1.ShanghaiUltraPrecisionOpticalManufacturingEngineeringCenter，DepartmentofOpticalScienceandEngineering，FudanUniversity，Shanghai200433，China；2.DepartmentofPhysics，COMSATSInstituteofInformationTechnology，Islamabad45550，Pakistan）Abstract：Notoriousterm'diffractionlimit'isnotactuallyatruebarrierunlesswearedealingwithfarfieldandlocalizationprecision.Thisdiffractionbarrierisnotimpenetrableandcanbebrokenwithsomeintelligenttechniques.Wediscussherefourpowerfultechniques，nearfieldscanningopticalmicroscopy（NSOM），stimulatedemissiondepletion（STED）microscopy，photoactivatedlocalizationmicroscopy（PALM）&stochasticopticalreconstructionmicroscopy（STORM）andstructuredilluminationmicroscopy（SIM），alongwiththeirunderlyingprinciplestogetherwithprosandcons.NSOMusesananometerscaledetectororsourcewhichcompelsthelighttopass龙源期刊网，laserlightisfocusedintoasmallspotbytheobjectiveandasaresult，allfluorophoreswithinthisfocusedspotradiatefluorescence，whichisthengatheredbytheobjectiveandheadedtothedetectorwhereitformsasinglepixel.FluorescentprobesareemployedbySTORM/PALM，whichareabletotogglebetweendarkstatesandfluorescentsothatwitheverysnapshottaken，onlyatiny，opticallyresolvableportionofthefluorophoresisobserved.Structuredilluminationisawidefieldtechniqueinwhichagridpatternisproducedbytheinterferenceofdiffractionorderswhicharesuperimposedonthesamplewhiletakingimages.STORMhastherelativelyhighpotentialtoeffectivelybreaktheconventionaldiffractionbarrierwithfewerhurdles.Keywords：diffractionlimit；nearfieldmicroscopy；threedimensionalmicroscopyIntroductionAmicroscopeisadeviceusedtoseeobjectsinintricatedetailusuallyuptotheorderofnanoscale.Themainfactorindeterminingthequalityofamicroscopeisitsresolutionwhichisfundamentallyboundedbydiffractionlimit.Normally，determiningthediffractionlimitofanimagingsystemisbasedonAbbeandRayleighcriterions[1]whichinturndependonnumericalapertureofthelensandwavelengthoflightbeingused.Withtheadventofnewtechnologiesdifferenttypesofmicroscopesworkingbeyondthelimitofdiffraction，havebeendevelopedwhichincludeelectronmicroscopes[23]usingelectronsaswellasopticalmicroscopesusingsmartopticaltechniques.Eachtypehasitsownprosandcons.Wepresentashortreviewofsomeoftheseopticalmicroscopes.1Nearfieldscanningopticalmicroscopy（NSOM）NSOMsometimesabbreviatedasSNOMforScanningNearfieldScanningOpticalMicroscopywasfirstlysuggestedin1928[4].NSOMusesaveryinnovativeconcepttopenetratethediffractionbarrierwhichistouseadetectororsourcewhosesizeisinnanometerscale.NSOMcompelsthelighttopassthroughthetinytip（whoseaperturesizeisontheorderoftensofnanometers）ofafiber.Nowifthistipisbroughtveryclosetotheobject，theresolutionisnomorelimitedbythediffraction，butbythesizeofthetipapertureaselucidatedinFig1.Soitmeansthedistancebetweenthetipandobjectmustbemuchsmallerthanλ.Soitbreaksthefarfieldresolutionlimit.Proberesolutionismainlyquantifiedbythediameteroftheaperture[5].Withthepassageoftime，moreandmoreadvancedtechniqueshavebeendevelopedandsomeareevenspecifictothetypeofsample[6].Thistechniquehasrevolutionizedthefieldofmaterialcharacterizationespeciallyfornanomaterials[7].SobasicallyNSOM/SNOMutilizesthenearfieldcomponentoftheelectromagneticwavewhosepropagationislimitedtoveryshortdistanceasopposedtofarfieldlightwhichsmearsoutinfinitelyuntilabsorbed，refractedorscatteredwhateveristhecase.Thepropagationdistanceofanearfieldphotonisproportionaltothephysicaldimensionsofitssource；henceinordertobeobservablebythenearfield，theobjectshavetobeinverycloseproximityofthefield.Thedistancebetweenthetipandobjectmustbelessthanthedimensionsoftheapertureofthetip.Theamplitudeof龙源期刊网[8].SimilarlyanothertechniquecalledaperturelessnearfieldmicroscopyreachesbeyondtherangeofsimpleNSOM[9].1.1Advantages（1）NSOMoffersdirectrelationshipbetweensurfacenanofeaturesandopticalorelectroniccharacteristicsalongwithconcurrentmensurationofthetopographyaswellasopticalproperties（fluorescence）.Fig.1SchematicdiagramofaNSOM（2）NSOMissubstantiallyeffectiveincharacterizingtheinhomogeneousmaterialsorsurfaces，likenanoparticles，polymerblends，poroussilicon，andbiologicalsystems[10].1.2Disadvantages（1）ThechiefdrawbacktoNSOMistherestrictednumberofphotonscomingoutofthetinytipandtheminisculecollectionefficiency.（2）Longscantimefo