THORLABS LDM21 User manual

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LDM21(/M)
5.6mm/9mm
LaserDiodeMount
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UserGuide
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TableofContents
Chapter1  Safety...................................................................1 
Chapter2  Description...........................................................2 
Chapter3  Setup....................................................................3 
3.6.1  TheoreticalResistanceValues............................................10 
Chapter4  Operation...........................................................12 
Chapter5  Troubleshooting.................................................14 
Chapter6  Specifications.....................................................16 
Chapter7  MechanicalDrawing...........................................17 
Chapter8  WarrantyandRMAInformation.........................18 
Chapter9  ThorlabsWorldwideContacts............................19 

5.6mm/9mmLaserDiodeMount Chapter1:Safety
Rev.L,March23,2023  Page1
Chapter1 Safety
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Warning
This unit must not be operated in explosive
environments.
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
Warning
Avoidexposure–laserradiationemittedfromapertures
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5.6mm/9mmLaserDiodeMount Chapter2:Description
Page2  TTN013394‐D02
Chapter2 Description
TheLDM21(/M)isatemperature‐controlled laser diode mount. When
usedwithThorlabsLDCSeriesLaserControllersandTEDSeriesTEC
Controllers, a laser diode can be operated with precise temperature
controlforwavelengthandpowerstability.Afourpinsocketacceptsall
9mmand5.6mmlaserdiodes.Easytousepolarityswitchesallowthe
lasermounttobeconfiguredforallpossiblelaserpinassignments.
TheLDM21(/M)wasdesignedwithfeaturesthatallowittobeeasily
incorporatedintocomplexsystems.ThefrontoftheLDM21(/M)hasan
SM1(1.035"‐40)threadtoacceptawide variety of Thorlabs SM11.0"
opticsmountsandaccessories.Alsostandardwiththemountare4‐40
tappedholeson 30mmcentersformountinganynumberofThorlabs
cageassemblyproducts.Therearealsofour8‐32(M4x0.7)tappedholes
toallowtheunittobepostmounted.
TheLDM21(/M)usesathermo‐electriccooler(TEC)topreciselyregulate
the operating temperature of a laser diode. Temperature sensingis
accomplished using an integrated thermistor and AD592 solid state
temperaturesensor.TheThorlabsTED200Csupportsthesesensors.
NOTE:TheLDM21(/M)isintendedforlaserdiodesrequiringlowinput
power and operating across a limited temperature range.  Its primary
functionis tomaintainthelaserdiode casetemperatureataconstant
temperature to within 0.2 °C, ideally at 25 °C in a typical laboratory
ambientenvironment(20to30°C).PleaserefertotheSafeOperating
AreachartinthismanualtoensurethattheLDM21(/M)isusedwithinits
capabilities.
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Figure1 InsideViewofLDM21andIncludedComponents

5.6mm/9mmLaserDiodeMount Chapter3:Setup
Rev.L,March23,2023  Page3
Chapter3 Setup
LaserInstallation
1. Unpackthelasermountandremovethefour2‐56socket‐head
screwsfromthefrontcoverusinga5/64"hexdriver(provided).
2. Remove the two Phillips head 2‐56 screws from the laser‐
mountingflangeandremovetheflange.
3. Determine the laser pin configuration from the laser diode
manufacturer’sdatasheetsandsettheLD(LaserDiode)andPD
(Photodiode)switcheslocatedontheinsideoftheunitaccording
toFigure2.
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Figure2 PolaritySwitchSettings
LD
Style A
Style B
Style C
Style D
AG CG
PD
CG AG
LD
AG CG
PD
CG AG
LD
AG CG
PD
CG AG
LD
AG CG
PD
CG AG
Case
LD PD
LD PD
LD PD
LD PD
Case
Case
Case

5.6mm/9mmLaserDiodeMount Chapter3:Setup
Page4  TTN013394‐D02
 The four sockets comprising the laser diode connector are
through‐hole type sockets with a blind clearance of 0.48”
(1.22cm)measuredfromthefrontfaceofthecoppercoldplate.
Itisnotnecessarytotrimthelaserdiodeleadspriortomounting
intothisconnectorunlesstheyarelongerthan0.48”(1.22cm).
 Thelaserconnectorislocatedcloseenoughtothefrontfaceof
thecoppercoldplatetoalloweasyinstallationofshort‐leaded
lasers. The clearance area around the LD and PD sockets is
sufficienttopreventthepinsfromcontactingthecoldplate.
 Mostlaserdiodesarethreepinswiththecasetiedtooneofthe
laserpinsandalsotooneofthephotodiodepins.Theotherlaser
and photodiode pins will be isolated from the case. The
LDM21(/M) was designed to operate the laser case at ground
potential,thereforethiscommonpinwillbeinsertedintoeither
the12o’clockorthe6o’clockpositionofthelaserconnector.
Locatetheisolatedlaserpinandinsertitinthe3o’clockposition.
Theisolatedphotodiodeshouldnowbeinthe9o’clockposition.
Refer to Fig. 3. (Orient the mount with the PD polarity switch
abovetheLDsocket).
 TheLDM21(/M)MountisalsocompatiblewithstyleEandstyle
Hlaserdiodes,whichdonothaveaphotodiode;theyhaveonly
alaserdiodeandagroundpin.Theycanthereforebesetupthe
same as style A (LD Anode Ground) or style B (LD Cathode
Ground)respectively.
 Replace the laser mounting flange and the cover. Install both
screwsthroughthemountingflangeandlooselyintothemount.
Carefullytighteneachscrewalittlebitatatimeuntiltheflange
isjustsnug.Donotover‐tighteneitherscrew‐theflangeshould
sitslightlyabovethecoldplate.Reinstallthecoverusingthefour
2‐56capheadscrewsprovided.

5.6mm/9mmLaserDiodeMount Chapter3:Setup
Rev.L,March23,2023  Page5

Figure3 LDandPDOrientation
5.6mmAdapter
Bydefault,theLDM21(/M)isdesignedtobeusedwithstandard9mm
laserdiode packages.Themountcanbeusedwithastandard 5.6mm
using the included adapter, which can be found in the small brown
envelopemarked“Accessories”ontheoutside.Includedinthisenvelope
isthe9mmmountingplateandtheimperialtometricmountingadapter.
4‐PinLaserDiodes
TheLDM21(/M)alsosupports4‐pinlaserdiodes.Insertthelaserintothe
4‐pinsocketandnotewhichlaserpinisinthe3o’clockposition(laser
anodeorcathode). Also note whichphotodiode pin is inthe9 o’clock
position(anodeorcathode).Themountwilltiethelaserandphotodiode
pinslocatedat12o’clockand6o’clocktogetherandalsotoground.By
notingwhichpolaritypinsareinsertedintothesocket,youcanconvert
the4‐pinlayouttooneofthe3‐pinlayoutsinFigure2onpage3.Setthe
LDandPDpolarityswitchesaccordingly.
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G
G
LDPD

5.6mm/9mmLaserDiodeMount Chapter3:Setup
Page6  TTN013394‐D02
LaserControllerConnections
UsingtheThorlabsLDC/ITCSeriesLaserControllers:
 TheLDM21(/M)iscompatiblewithallThorlabsLDCLD
controllersandITCseriescombinationcontrollers(LDandTEC).
Appropriate cables with DB9 connectors are included with
Thorlabs controllers and ensure that the controllers cannot be
connectedincorrectly.Additionally,thesecontrollershavebuilt‐
inprotectioncircuitrythatprotectsthelaserwhennotinuse.
 ThenomenclaturefortheLaserDiodepolarityswitchonthe
LDC/ITC driver and the LDM21(/M) are consistent with each
other.Forexample,ifthelaserpolarityonthedriverissetto
“AG” (anode grounded), then the LD polarity switch on the
LDM21(/M)shouldalsobesettoAG,andsoforth.
 ThenomenclatureforthePhotoDiodepolarityswitchonthe
LDC4000SeriesBenchtopControllers,PRO8LaserDiodeCurrent
ControlModules,andITCseriesdriversandtheLDM21(/M)isas
follows:ThephotodiodepolarityswitchontheLDM21(/M)must
alwaysbesetto“CG”.Thephotodiodepolarityshouldbesetwith
theinternalLasercontrollerswitchonly.Formoreinformation
onhowtosetPolaritysettingsontheLasercontroller,please
refertotheappropriateLaserControllermanual.
Usingathird‐partylasercontroller:
 Whenusingathird‐partycontroller,acustomcablewillhaveto
bemadetoproperlyinterfacetothelasermount.Pleasereferto
thetableonthenextpageforlaserconnections:



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5.6mm/9mmLaserDiodeMount Chapter3:Setup
Rev.L,March23,2023  Page7
Pin Signal Description
1Interlock
(LDCSpecific)
ThispinistheinputtotheInterlockCircuits.
WhenusingThorlabsLDCs,noexternalcircuitry
isrequired.
2Photodiode
Cathode
Thispinisconnectedtothe9o’clockpinonthe
lasersocketwhenthePDPolaritySwitchissetto
AG(AnodeGrounded).Itisattachedtoground
andthe12o’clockand6o’clockpinsonthelaser
socketwhenthePDPolaritySwitchissettoCG
(CathodeGrounded).
3LaserGround
(Case)
Thispinisconnectedtothe12o’clockand6
o’clockpinsonthelasersocketandcorresponds
tothesettingsoftheLDandPDpolarity
switches.i.e.,iftheLDandPDswitchesareset
toAG,thenthispingroundstheAnodesofthe
laserandphotodiode.
4 Photodiode
Anode
Thispinisconnectedtothe9o’clockpinonthe
lasersocketwiththePDPolaritySwitchissetto
CG(CathodeGrounded).Itisattachedtoground
andthe12o’clockand6o’clockpinsonthelaser
socketwhenthePDPolaritySwitchissettoAG
(AnodeGrounded).
5 Interlock
Return
ThispinisthereturnsideoftheInterlock
circuitry.Pins1and5areshortedinternallyin
theLDM21(/M).
6 N/A 
7 LaserDiode
Cathode
Thispinisconnectedtothe3o’clockpinonthe
lasersocketwhentheLDPolaritySwitchissetto
AG(AnodeGrounded).Ifthepinisnot
connected,itwillbefloating
8 LaserDiode
Anode
Thispinisconnectedtothe3o’clockpinonthe
lasersocketwhentheLDPolaritySwitchissetto
CG(CathodeGrounded).Ifthepinisnot
connected,itwillbefloating
9 N/A 

5.6mm/9mmLaserDiodeMount Chapter3:Setup
Page8  TTN013394‐D02

TECControllerConnections
UsingtheThorlabsTEDSeriesTECControllers:
 TheLDM21(/M)isbestusedwithThorlabsTED200Correlated
TECControllers.TheTEDseriesareshippedwithamatingDB9
cable that plugs directly into the controller and laser mount.
UsingthecablesuppliedwiththeTED,thecontrollercannotbe
connected incorrectly. Simply connect the cable included with
theTEDtotheLaserMountandtothecontroller.
Usingathird‐partyTECcontroller:
 Whenusingathird‐partycontroller,acustomcablewillhaveto
bemadetoproperlyinterfacetothelasermount.Pleasereferto
thetablebelowforlaserconnections.
Pin Signal Description
1 N/A N/A
2 Thermistor(+) The10kΩ@25°CNTCthermistor(providedfor
temperaturefeedback).
3 Thermistor(‐) Thethermistorreturnpin
4 TEC(+) ThispinisconnectedtothepositiveterminaloftheTEC
element.
5 TEC(‐) ThispinisconnectedtothenegativeterminaloftheTEC
element.
6 N/A N/A
7 AD592(‐)
ThenegativeterminaloftheAD592temperature
transducer.WhenusingThorlabsTEDs,noexternal
circuitryisrequired.Tousethisdevicewiththirdparty
controllers,itmustbeproperlybiased.RefertoAnalog
DevicesAD592Dataforapplicationinformation.
8 N/A N/A
9 AD592(+) ThepositiveterminaloftheAD592

5.6mm/9mmLaserDiodeMount Chapter3:Setup
Rev.L,March23,2023  Page9
ThermistorData











Figure4 ThermistorCurveandData

Resistance(Ω) °C  Resistance(Ω) °C
15895 15 9563 26
15153 15 9149 27
14451 17 8755 28
13785 18 8380 29
13155 19 8023 30
12558 20 7684 31
11991 21 7362 32
11454 22 7055 33
10944 23 6762 34
10460 24 6484 34
10000 25 

5.6mm/9mmLaserDiodeMount Chapter3:Setup
Page10  TTN013394‐D02
3.6.1 TheoreticalResistanceValues
The relationship between resistance and temperature can also be
calculatedusingthefollowingequations.
𝑅

𝑅

𝑒
󰇛//

 

󰇜
⁄

𝑇

󰇛𝐴

𝐵

ln󰇧 𝑅
𝑅

󰇨𝐶

ln

󰇧𝑅
𝑅

󰇨𝐷

ln

󰇧𝑅
𝑅

󰇨


WhereA,B,C,D,A
1
,B
1
,C
1
,andD
1
areconstantvaluesthatdependon
thematerial;seetablebelowforvalues.R
ref
istheresistancevalueata
referencetemperature,whichisroomtemperatureinthiscase.Tisthe
temperatureinK.

Constants Value Unit
A ‐14.6337 ‐
B 4791.842 K
C ‐115334 K
2

D 3.730535E+06 K
3

A
1
3.354016E‐03 ‐
B
1
2.569850E‐04 K
‐1

C
1
2.620131E‐06 K
‐2
D
1
6.383091E‐08 K
‐3
T
0
298.15 K
R
ref
10000 Ω

MountingOtherAccessories
TheLDM21(/M)includesaSM1threadedholecenteredonthelaserfor
mountingThorlabsSM1‐seriesopticmounts.Thisismostoftenusedfor
mountingasphericcollimatingopticsavailableseparatelyfromThorlabs.

5.6mm/9mmLaserDiodeMount Chapter3:Setup
Rev.L,March23,2023  Page11
Alsoincludedarefour4‐40tappedholesmountedon30mmcentersfor
attachingourcageassemblyproducts.UsingthecombinationoftheSM1
threaded mount and the cage assemblies’ products, a wide variety of
opticalsystemscanbeeasilyassembledfromoff‐the‐shelfproducts.







5.6mm/9mmLaserDiodeMount Chapter4:Operation
Page12  TTN013394‐D02
Chapter4 Operation
 Withthelasermountedandthelaserandtemperaturecontroller
connected,theLDM21(/M)isreadytooperate.Pleasereferto
theoperatinginstructionsforthelaserandtemperature
controllerforspecificoperatinginstructions.
 Whenoperatingatlowtemperaturesinhighhumidityclimates,
the laser mount may develop internal condensation. If this
occurs,turnthelaseroff,openthecase,andallowthemountto
dryoffcompletelybeforere‐using.
 Whenusingacollimatingopticinthe1"threadedmount,thelens
may be positioned slightly laterally by loosening the four 2‐56
screwsonthecoverandshiftingthecoverplatemanually.
SafeOperatingArea
TheLDM21(/M)isintendedtobeoperatedatafixedtemperatureset‐
pointof25°Cbutcanbeoperatedaslowas20°Caslongastheinput
powertothelaserdiode(inputcurrentxLDvoltage)doesnotexceedthe
valuesspecifiedintheSafeOperatingAreacurveasafunctionofambient
temperature.ItisnotrecommendedthattheLDM21(/M)bedrivenwith
morethan600mWofinputpower,settoatemperaturebelow20°C,or
operatedinanambienttemperatureabove35°C.Operatingthe
LDM21(/M) outside of the safe operating area will result in thermal
runaway of the cooling system which will damage the laser diode
mountedintheunit.
Additionally, the 2 W maximum cooling capacity includes the power
dissipatedbytheTECelementinadditiontotheinputpowerofthelaser
diode.CarefulmonitoringoftheTECpower(TECCurrentxTECVoltage)
alongwiththeparametersoftheSOAcurvewillfurtherensurethatthe
systemisoperatingwithinitscapabilities.

5.6mm/9mmLaserDiodeMount Chapter4:Operation
Rev.L,March23,2023  Page13

MaintainingtheLDM21(/M)
TherearenoserviceablepartsintheLDM21(/M).Thehousing maybe
cleanedbywipingwithasoftdampcloth.Ifyoususpectaproblemwith
yourLDM21(/M),pleasecallThorlabsTechnicalSupport,andanengineer
willbehappytoassistyou.




5.6mm/9mmLaserDiodeMount Chapter5:Troubleshooting
Page14  TTN013394‐D02
Chapter5 Troubleshooting
1. LaserDriverwillnotenable.
 If you are using our laser and TEC controllers with our
LDM21(/M) mount, make sure that both cables are fully
insertedintotheirDB9connectors.
2. Laser wavelength or power is unstable even though the TEC
controllershowsastabletemperature.
 Make sure that your laser diode is fully inserted into the
LDM21(/M)lasersocketandthatitsbodyisinfullcontact
withthecoppercoldplate.
 Makesurethattheappropriatemountingflangeisinstalled
over your laser. There are two different flanges; one
specificallyfor5.6mmdiodesandonefor9mmdiodes.
3. TheLDCserieslaserdriverindicatesan“OpenCircuit”alarm
whenItrytoenablethelaser.
 TheLDandPDpolarityswitchsettingsareincorrect.Referto
Fig.1andthedatasheetforyourspecificlaserdiodeto
ensurethepropersettings.TheLDpolarityswitchsettingon
yourLDM21(/M)mustalsomatchtheLDpolarityswitchon
therearpanelofyourLDCserieslaserdiodecontroller.
 Thelaserdiodeisinstalledintothewrongpinsonthelaser
diodesocket.RefertoFig.2forthecorrectorientationofthe
laserdiodepinsandcomparethistothedatasheetforyour
laserdiode.
4. My laser diode does not have an integrated photodiode. How
doesitgetinstalled,andhowdothepolarityswitchesgetset?
 Ifyourlaserdiodehasoneofitstwoactiveleadscommonto
thecaseofthelaser,thatleadmustbeconnectedtooneof
the“G”socketsonthelaserdiodeconnector(refertoFig.2)
whiletheotherpinisconnectedtothe“LD”socketinthe3
o’clock position. Depending on the pin orientation of your
laser,youmightbeusingeitherthe“G”socketat12o’clock

5.6mm/9mmLaserDiodeMount Chapter5:Troubleshooting
Rev.L,March23,2023  Page15
orthe“G”socketat6o’clock.Refertoyourlaserdiodedata
for pin orientation. If your cathode pin is common to the
bodyofyourlaserdiode,settheLDpolarityswitchto“CG”.
Ifyouranodepiniscommontothebodyofyourlaserdiode,
set the LD polarity switch to “AG”. The setting for the PD
polarityswitchisirrelevant.
Ifyoustillhaveproblemsorquestionsregardingtheoperationofyour
LDM21(/M),pleasecontactThorlabsTechSupport.




5.6mm/9mmLaserDiodeMount Chapter6:Specifications
Page16  TTN013394‐D02
Chapter6 Specifications
Item# LDM21(/M)
General
Size 1.75"x1.75"x1.66"
(44.5mmx44.5mmx42.1mm)
Weight 3oz(0.08kg)
AccessoryMounting
1.035"‐40ThreadforSM1SeriesOpticsMounts
4‐40x30mmTappedHolesforCageAssembly
Products
MountingHoles LDM21:8‐32orLDM21/M:M4
LaserSpecifications
LasersSupported 5.6mmand9mm
MaxLaserCurrent 500mAa
MaxLaserInputPower 600mWa
LaserPin Ø5.6andØ9.0mmLaserDiodes
A,B,C,D,E,andHConfigurations
Configurations Selectable
LaserPolaritySelect SlideSwitches
LaserInterface DB9Female
TECSpecifications
MaxTECCurrent 2.5A
MaxTECVoltage 1.8V
TECHeating/
CoolingCapacity 2W
TypicalTemperatureRange(LDdependent)
TemperatureRange 20–30°C
TempSensor1
Thermistor
10kΩ±3%,NTC
Beta=3977K±0.75%
TempSensor2
AnalogDevicesAD592 1µA/K
TECInterface DB9Male
a.SeeSafeOperatingAreaonpage14formoreinformation.