Quantum Instruments Cascade Laser Starter Kit Photoacoustic detection, Photoacoustic technique

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Starter Kit Instruction Manual

Maintenance

9.1.3Photoacoustic detection

In the photoacoustic detection, the optical beam is periodically modulated in amplitude before illumi- nating the cell containing the absorbing chemical. The expansion generated by the periodic heating of the chemical creates an acoustic wave which is detected by a microphone.

The two very important advantages of photoa- coustic detection are:

•a signal is detected only in the presence of absorption from the molecule;

•no mid-IR detectors are needed.

For these reasons, photoacoustic detection has the potential of being cheap and very sensitive. How- ever, ultimate sensitivity is usually limited by the optical power of the source.

a.c. modulation of	Detection of the
the laser amplitude	acoustic wave at w
w
QC Laser	Chemical Cell
	Microphone

Fig.53: Photoacoustic technique

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Contents Instructions Manual Web version Quantum Cascade Laser Starter KitContents Use InstallationTroubleshooting Maintenance OverviewAppendix Manufacturer IdentiﬁcationDocument Limited warantyCompliance GeneralChapter overview GeneralitiesPersonnel GlossaryPersons ProductDescription style Commands styleProcedure style Typographic conventionsPossible cause ProblemProcedure eﬀects style See page x-y Troubleshooting stylePage Introduction Safety InstructionsImportance of safety instructions Non-compliance with the safety regulationsEnvironmental conditions General safety instructionsCompliance and informa- tion System Composition DescriptionGeometry of QC lasers DFB and FP Quantum Cascade LasersIf no conﬁguration is speciﬁed, the DN pad is used DescriptionSpeciﬁcations Electrical model Electrical model characteristicsLLH100 external view description Laboratory Laser HousingLLH100LLH100 internal view Laboratory Laser Housing internal viewThermo-Electric Cooler TEC and PT100 connections Speciﬁcations of the Peltier connectorMeasurement connection Speciﬁcations of the measurement connectorQCL pulser switching unit front and rear view QCL pulser switching unitLDD100Timing data QCL pulse switching measuring unitGeneralities Measured voltagesDuty cycle calculation Laser peak currentAverage dissipation Laser peak voltageAccuracy considerations QCL pulser timing unit TPG128 Trigger and logic output signals Ω TTL driver circuitPeltier and PT100 connections QCL temperature controllerTCU151Standard items InstallationChapter overview Packing list GeneralProcedure Setting the appropriate AC voltage on TCU151110-120V, 60Hz USA 220-240V, 50Hz Europe Before beginning Installing the starter KitConnecting Starter Kit QCL pulse timing unit com- mand description UseTCU151 temperature controler front panel TCU151 command descriptionOverview Laser utilisationProceedings Starting the TPG128 Interlock utilisation Procedure Interlock utilisationPrinciple TroubleshootingPower supply reaches max cur- rent for a very low voltage DC power supply is not ﬂoatingThere is no contact with the laser Laser draws current but gives no lightLaser does not draw current QCL laser is not used with the LLH and is groundedHow to remove the covers of TCU151 and TPG128 MaintenanceOverview Quantum Cascade Laser replace Ment Replacement procedures+ LLH100 connection Facet on the case, it is extremely fragileExchanging the laser QCL UP and DN position ExchangeHumidity If the ambient atmosphere is humid this isNeeded material TCU151 temperature con Troller interlock settingProcedure interlock setting Before beggining interlock set TingGeneralities Calibaration proceduresProcedure calibration 1 TPG128 calibrationTPG128 main board TPG128 main board Procedure +5V/-5V power supply check 2 TCU151 temperature controller calibration= 1.22 to Sensing level and range adjustementTemperature Reference oﬀset adjustment LCD screen should display 1.00 a Current/Voltage ratio adjustmentSetting Oscillator checkStarting the power section of the instru Ment 7V = 70 C If needed, adjust it with the trimmer P92→ Value displayed ≤ 1A Current adjustment→ Value displayed should tend to the deﬁned value → The red LED 1 should turn oﬀ Miscellaneous functions testing Temperature Limit testing→ The temperature displayed 2 should be 035 C Threshold onFrequency modulation technique Tildas Application notesDetection techniques Direct absorptionPhotoacoustic technique Photoacoustic detectionBias Circut Bias-T AppendixGeneral Utilisation What has to be kept in mind before use? Avoid reverse polarity on the input Current and voltage ranges of the Bias-T cir- cuitUnpacking instructions for NS submounts Unpacking NS laser from its transportation box