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THROUGHPUTOFANOPTICALINSTRUMENT

CHEM314

OBJECTIVES

CalculatethenumberofphotonspresentinasinglebeamUV-Vis:

•  Atthesource•  Enteringthemonochromator•  IncidentonthediffracJongraJng•  Emergingfromthemonochromator•  Incidentonthesample•  Emergingfromthesample•  Incidentonthedetector

Calculatethenumberofelectronsgeneratedbythephotonsonthedetector.

Examinedetectorcurrenttovoltageconverterelectronics.

Calculatethevoltagemeasuredfromthedetector.

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BUILDINGASPECTROSCOPICINSTRUMENT

Components1.  StableradiaJonsource

2.WavelengthisolaJon-monochromator3.Transparentsampleholder/opJcs4.Detector5.Signalprocessing

TASKS:PARTSA-C1.   Measuredistances(page2)onthespectrometer.

2.   CutandweightheoutputspectrumtodeterminefracDonofemissionin450-550nmrange.

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ConJnuumsourceswithconstantoutputasafuncJonofwavelengthrequiredformolecularspectroscopy

SOURCES

TUNGSTENFILAMENT

Outputspectrumat2870K

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BLACKBODYRADIATION

h^ps://docs.kde.org/stable/en/kdeedu/kstars/ai-blackbody.html

Wein’sDisplacementLaw

λmax=maxoutputλT=temp(K)L=luminosityA=surfaceareaα=constant

A-MEASURINGTHEINSTRUMENT

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B-CUTTINGANDWEIGHING

C-PHOTONSCOLLECTEDININITIALOPTICS

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OBJECTIVES

CalculatethenumberofphotonspresentinasinglebeamUV-Vis:

•  Atthesource•  Enteringthemonochromator•  IncidentonthediffracJongraJng•  Emergingfromthemonochromator•  Incidentonthesample•  Emergingfromthesample•  Incidentonthedetector

Calculatethenumberofelectronsgeneratedbythephotonsonthedetector.

Examinedetectorcurrenttovoltageconverterelectronics.

Calculatethevoltagemeasuredfromthedetector.

TASKS:PARTSD-E1.   Calculatethephotonsenteringthemonochromator

2.   CalculatethenumberofphotonsexiDngthemonochromator PointSource

Collimatedlight

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COLLIMATINGMIRRORSourcemirrorfuncDonstocollectphotonsfromthelightsourceandmakesthephotonstravelparalleltooneanother

Whereinthisdiagramisthelightsourcelocated?

Whatistheradiusofcurvatureofthesourcemirror?

R=2f

PointSource

Collimatedlight

OVERANDUNDERFILLEDOPTICS

Underfilledsourcemirror

Overfilledsourcemirror

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REFLECTIONGRATINGPERFORMANCE

MONOCHROMATORPERFORMANCE

λ1>λ2

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MONOCHROMATORCALCULATIONAnechelleMegraDngthatcontains1200blazespermmwasirradiatedwithapolychromaDcbeamatanincidentangleof29°tothegraDngnormal.Calculatetheangleatwhichfirstorder500nmlightwillappear.

OBJECTIVES

CalculatethenumberofphotonspresentinasinglebeamUV-Vis:

•  Atthesource•  Enteringthemonochromator•  IncidentonthediffracJongraJng•  Emergingfromthemonochromator•  Incidentonthesample•  Emergingfromthesample•  Incidentonthedetector

Calculatethenumberofelectronsgeneratedbythephotonsonthedetector.

Examinedetectorcurrenttovoltageconverterelectronics.

Calculatethevoltagemeasuredfromthedetector.

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TASKS:PARTSG-F1.   Determinefluxatdetectorwithablankandsample

2.   CalculatethecurrentatthePMTanodewithablankandsample

3.   Examinedetectorelectronics

OPTICSANDSAMPLEHOLDERS

01234

190 490 790 1090

Absorban

ce

Wavelength(nm)

Quartz PlasJc

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REFRACTIVEINDEX-OFGLASS

REFRACTIVEINDEX-OFWATER

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SAMPLE-CUVETTEINTERACTIONCalculatethepercentageofthebeamlosttoreflecDonat500nmwhenitpassesthroughthecuveMe.

Glass

Glass

AnalyteSoluJonA=0.4at500nm

AirAir

1.  SoluJonfactors2.  Non-monochromaJclight3.  Notanalyzingatλmax4.  Straylight5.  Mismatchedcuve^es6.  Instrumentnoise

Toomuchortooli^leabsorpJon

SOURCESOFNONLINEARITYOFBEER’SLAW

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DETECTORRESPONSE

PHOTOMULTIPLIERTUBE(PMT)

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UV-VISELECTRONICCIRCUIT

CURRENTTOVOLTAGECONVERTER

Measurevoltage

OperaJonalamplifier

•  Lowresistancetosourcecurrent

•  Preventsloadingerrorduringcurrentmeasurement•  HighamplificaDonofsignal

OPERATIONALAMPLIFIERManyresistorsandtransistorsonasinglechip

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OPERATIONALAMPLIFIERS

OriginallyappliedtoanalogcomputerstodosimplemathfuncDons.

•  Largeopenloopgains(104-106)-largeamplificaDon.

•  Highinputimpedance(108-1015Ω)-doesn’tmesswithcurrentfromPMT.

•  Lowoutputimpedance(0.001-1Ω)-doesn’tmesswithreadingvoltage.

•  Verylowdarkcurrent-whichcanbeeasilyoffset.

CURRENTTOVOLTAGECONVERTER

Currenttovoltageconverter

Currentshunttoground

Voltagereadout

Darkcurrentadjustment

Capacitorstabilizesoutputvoltage