Quantum Instruments Cascade Laser Starter Kit manual Appendix, Bias Circut Bias-T, General

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Chapter 10

Appendix

10.1Bias Circut (”Bias-T”)

10.1.1General

The Bias-T allows to apply a constant (DC) cur- rent to the laser in addition to the pulsed current (therefore a Bias-T is useless in CW mode). The current is drawn from the external (user supplied) power supply through the laser. This current can be controlled electrically.

Since tuning of a QC laser is done by changing the temperature of the active zone, the DC Bias cur- rent can be used to control the emission wavelength of the laser via its heating eﬀect. The Bias-T there- fore allows for electrically controlled rapid scanning of the emission wavelength. The achievable shift is of the order of 0.1%, with a Bias frequency of up to 100Hz.

10.1.2Description

The circuit included in the LDD100 pulser unit is controlled by the twisted black and yellow wires of the control cable (with the DSUB-9 plug). They correspond to the shield and center of the IN con- nector in the former case (positive voltage on yellow wire). This version has no monitor connection.

				Low Impedance Line
	+VDC			LLH
				LLH
	R			L
User	R
User
DC
Power			Bias−T
Supply			Bias−T
Supply	Q
	Q
		U_in	T1	U_mon
				U_mon

	GND			R
				R
				i_b
	Control "IN"
			Monitor "MONI"
	LDD100

Fig.53: Bias circuit diagram block

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Contents Quantum Cascade Laser Starter Kit Instructions Manual Web versionContents Installation TroubleshootingMaintenance Overview UseAppendix Identiﬁcation DocumentLimited waranty ManufacturerGeneral Chapter overviewGeneralities ComplianceGlossary PersonsProduct PersonnelCommands style Procedure styleTypographic conventions Description styleProblem Procedure eﬀects styleSee page x-y Troubleshooting style Possible causePage Safety Instructions Importance of safety instructionsNon-compliance with the safety regulations IntroductionCompliance and informa- tion General safety instructionsEnvironmental conditions Description System CompositionDFB and FP Quantum Cascade Lasers If no conﬁguration is speciﬁed, the DN pad is usedDescription Geometry of QC lasersSpeciﬁcations Electrical model characteristics Electrical modelLaboratory Laser HousingLLH100 LLH100 external view descriptionLaboratory Laser Housing internal view LLH100 internal viewSpeciﬁcations of the Peltier connector Thermo-Electric Cooler TEC and PT100 connectionsSpeciﬁcations of the measurement connector Measurement connectionQCL pulser switching unitLDD100 QCL pulser switching unit front and rear viewQCL pulse switching measuring unit GeneralitiesMeasured voltages Timing dataLaser peak current Duty cycle calculationAccuracy considerations Laser peak voltageAverage dissipation Trigger and logic output signals Ω TTL driver circuit QCL pulser timing unit TPG128QCL temperature controllerTCU151 Peltier and PT100 connectionsInstallation Chapter overview Packing listGeneral Standard items110-120V, 60Hz USA 220-240V, 50Hz Europe Setting the appropriate AC voltage on TCU151Procedure Installing the starter Kit Before beginningConnecting Starter Kit Use QCL pulse timing unit com- mand descriptionTCU151 command description TCU151 temperature controler front panelProceedings Laser utilisationOverview Starting the TPG128 Procedure Interlock utilisation Interlock utilisationTroubleshooting Power supply reaches max cur- rent for a very low voltageDC power supply is not ﬂoating PrincipleLaser draws current but gives no light Laser does not draw currentQCL laser is not used with the LLH and is grounded There is no contact with the laserOverview MaintenanceHow to remove the covers of TCU151 and TPG128 Replacement procedures Quantum Cascade Laser replace MentFacet on the case, it is extremely fragile + LLH100 connectionQCL UP and DN position Exchange Exchanging the laserIf the ambient atmosphere is humid this is HumidityTCU151 temperature con Troller interlock setting Procedure interlock settingBefore beggining interlock set Ting Needed materialCalibaration procedures Procedure calibration1 TPG128 calibration GeneralitiesTPG128 main board TPG128 main board 2 TCU151 temperature controller calibration Procedure +5V/-5V power supply checkSensing level and range adjustement = 1.22 toTemperature Reference oﬀset adjustment Current/Voltage ratio adjustment SettingOscillator check LCD screen should display 1.00 a7V = 70 C If needed, adjust it with the trimmer P92 Starting the power section of the instru Ment→ Value displayed should tend to the deﬁned value Current adjustment→ Value displayed ≤ 1A Miscellaneous functions testing Temperature Limit testing → The temperature displayed 2 should be 035 CThreshold on → The red LED 1 should turn oﬀApplication notes Detection techniquesDirect absorption Frequency modulation technique TildasPhotoacoustic detection Photoacoustic techniqueGeneral AppendixBias Circut Bias-T Utilisation What has to be kept in mind before use? Current and voltage ranges of the Bias-T cir- cuit Avoid reverse polarity on the inputUnpacking NS laser from its transportation box Unpacking instructions for NS submounts