24 Chapter 4. Troubleshooting
thecateye lens,usingthefocus adjusttoolprovided withyourlaser,
or a small screwdriver, until the power increases to a peak.
10. Reducetheinjectioncurrenttoobtain1mW,followedbyfocusad-
justmentofthecateyelens,anditerateuntiltheminimumcurrent
threshold is achieved.
11. Turn offthe current,reassemble thelaser andadjust the filterangle
to achieve the desired wavelength, as noted at step 2.
12. Turnonthecurrentabovethreshold,butnotexceedingthemaximum
safecurrentspecifiedinthelasertestreport, andfine-adjustthe
filterangletoachievethedesiredwavelengthbymonitoringone.g.a
MOGLabs FZWFizeau wavemeter.
13. Increase thelaser diodecurrentto thedesired operatingcurrent,
thendoafinaloptimisationoftheCEL outputpoweratthiswave-
length by adjusting the diode fine-focus adjust.
4.4 Fibre coupling
Lasers with extended chassis canbe fitted witha fibreconnector to allow
coupling thefree-spacelaserbeamintoasingle-modeopticalfibre. Two
mirrorsonkinematicmountsallowprecisealignmentofthepositionand
angleof the laserbeam into thefibrecoupler: a commonandfamiliar
arrangementforopticalscientists(seefigure3.6). Thearrangementcan
alsobeconfiguredtoallowsplittingtheoutputintotwobeams,usinga
PBSas the first reflector.
Giventhe8%Fresnellossfromentranceandexitfacetsofthefibre,the
maximum theoretical efficiencyfor single-modefibre coupling is92%.The
stainlesssteelkinematicmirrormountsarestableandeasytouse,and
coupling efficiency of over 70% is easily attained at 780nm.
Alignmentrequiresfirstadjustingthemirrorssothatthebeamexitsthe
laserchassisinthecentreofthefibrecouplingport,andparalleltothe
longaxisofthechassis. Thefibrecouplercanthenbeinstalled,without
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