铷原子的饱和吸收光谱和频率调变光谱Word下载.docx

铷原子的饱和吸收光谱和频率调变光谱Word下载.docx

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and

FrequencyModulationSpectroscopy

ofRubidiumAtoms

DanLee

Grade98,SchoolofPhysics,DepartmentofTechnicalPhysics

摘要

在这个实验中，我们测量了85Rb和87Rb原子的饱和吸收光谱和频率调变光谱．在饱和吸收光谱中，87Rb原子的|F=1〉→|F＇=0,1,2〉和|F=2〉→|F＇=1,2,3〉,85Rb原子的|F=2〉→|F＇=1,2,3〉和|F=3〉→|F＇=2,3,4〉以及它们的交错信号都被完全的捕捉住.这里,F表示的是5S1/2基态的超精细能级，而F＇则表示的是5P3/2激发态的超精细能级.87Rb原子的｜F=2〉→|F＇=1,2,3〉的谱线则被用于调频技术．

Abstract

WehavemeasuredD2transitionsof85Rband87Rbatomswithsaturatedabsorptionspectroscopyandfrequencymodulationspectroscopy.Thesesaturatedabsorptionspectra,|F=1〉→|F’=0,1,2〉and|F=2〉→|F’=1,2,3〉of87Rbatoms,|F=2〉→|F’=1,2,3〉and|F=3〉→|F’=2,3,4〉of85Rbatoms,andtheircrossoverlinesarecompletelyresolved,whereFindicatesthehyperfinelevelofthe5S1/2groundstateandF’indicatesthatofthe5P3/2excitedstate.Thederivativesofthe|F=2〉→|F’=1,2,3〉spectraof87Rbatomsareobtainedwiththetechniqueoffrequencymodulation.

Asweknow,theRubidiumatomisonekindofboson.ItobeystheBose-Einsteinstatistics.In1995,RubidiumatomwassuccessfullyusedtorealizetheBose-Einsteincondensation.

Inthenature,therearetwotypesofisotopesofRubidium:

87Rband85Rb.Ifweconsiderthehyperfinestructureoftheisotopesof87Rband85Rb,wecangetthefiguresfortheirenergylevels.Thehyperfinestructureisresultedfromthespinofthenucleus,whichiscalledZeemaneffectthatcanleadtotheseparationoftheenergylevelsinmagneticfield.

Fig.1belowshowsusthehyperfinestructureofthe87Rb.

Fig.1.Thehyperfinestructureoftheenergylevelsof87Rb

Fig.2belowshowsusthehyperfinestructureofthe85Rb.

Fig.2.Thehyperfinestructureoftheenergylevelsof85Rb

Thetwofiguresaresimilartoeachother.Thesmalldifferencebetweenthemisthattheseparationofenergylevelsof85Rbislessthanthoseof87Rb.Anotherdifferencebetweenthetwoisotopesisthatthespinofthenucleusof87Rbis3/2andthatof85Rbis5/2.

Ididsuchafollowingexperimenttostudythemainenergylevelandthespectrumatfirst.TheexperimentalsetupisshownschematicallyinFig.3.

Fig.3.ExperimentalsetupfortheabsorptionspectrumoftheRubidium

Thediodelaserisdrivenbythecurrentfromthelaserdiodedriverandiscontrolledbythetemperaturecontroller.

Wechoosethediodelaserasthelaserresourceherebecauseithastoomanyadvantages:

theinexpensiveprice,thesmalllinewidththatislessthan100kHz,thehighoutputpowerwhichcanreachmorethan10mW,thelargetunablerangeofwavelengthwhichismorethan20nm,thehighstabilityandthehighsensitivity.Allabove,themostimportantmeritisthatitcanprovidethelaserwhosefrequencyisjustwhatweneedinsuchexperiments.

Inthisexperiment,wealsouseafunctiongeneratortooutputatriangularwavewithappropriatefrequencyandamplitude.Weinputthiswaveintothelaserdiodedriverandthenmakethelasercurrentchangeinaproperrange.Theamplitudeofthetriangularwavedecidestherange.Sothewavelength（orfrequency）ofthelaserchangeswiththetriangularwave.TheRubidiumatomwillabsorbsomephotonsfromthelaserwhentheirfrequencyisproper.ThespectrumisshowninFig.4,wheretheamplitudeofthetriangularwaveis200mVanditsfrequencyis80MHz.

Fig.4.TheabsorptionspectrumoftheRubidium

Onethingthatwemustemphasizeiswhywedonotchoosethesquarewaveorserratedwavebuttriangularwave.Thecurrentfromthelaserdiodedriverthatdrivethelasercannotbechangedtoodrastically.Otherwisethediodelaserwouldbedamaged.

FromtheFig.4,wecanseethefourapparentspectralines.Fromrighttoleft,wemarkthemasa,b,c,d.

Infact,eachlineofa,b,c,dcontainsfinespectra.Thea-linecontainsthespectralinesfrom87Rb|5S1/2,F=2>

to|5P3/2,F’=1,2,3>

.Theb-linecontainsthespectralinesfrom85Rb|5S1/2,F=3>

to|5P3/2,F’=2,3,4>

.Thec-linecontainsthespectralinesfrom85Rb|5S1/2,F=2>

.Thed-linecontainsthespectralinesfrom87Rb|5S1/2,F=1>

to|5P3/2,F’=0,1,2>

.

ButbecauseoftheDopplerbroadeningeffect,wecannotdistinguishthefinespectralines.Thereasonisinteresting.Weknowthatonlytheatomscanabsorbacertainkindofphotonswhoseenergy（orfrequency）exactlymatchestheseparationoftheenergylevelofthestaticatom.Infact,alltheatomsmoveinalldirections.DuetoDopplereffect,theatomcanbeexcitedbythosephotonswhosefrequencyisslightlyawayfromtheexactones;

meanwhiletheseparationamongtheenergylevelsofthehyperfinestructureofRubidiumistiny,too.Allofaboveleadtotheresultthatwearenotabletodistinguishthefinespectra.

Ifwewanttodistinguishthesefinespectra,wecanusethemethodtogetthesaturatedab