Specifications

14 Chapter 3. Alignment
7. Ifpossible,scanthelaserthroughanatomicresonanceand
view the absorption on an oscilloscope. With current bias
disabled (DIP4on aMOGLabscontroller)andfull span,you
shouldseeareasonablefractionoftheabsorptionspectrum,
withoneormoremode-hops. A Fabry-Perot etalonorafast
high-resolutionwavemeter(MOGLabsMWM)canalsobeused
to optimise the mode-hop-free range.
8. Adjustthefilterangle,andtheinjectioncurrent,tooptimise
thescanssothat youseethemaximumnumberofrepeatsand
the deepest signals.
9. Checkthatthesaturatedabsorptiontracesareclean. Noisy
spectraindicatemulti-modeoperation,orhighlinewidth,which
may bedue toweak feedback.Thelasing thresholdis agood
diagnostic:lowerthresholdindicatesbetterfeedbackandcon-
sequently lower linewidth.
A scanning Fabry-Perot or a MOGLabs MWM wavemeter is a
veryusefuldiagnostictooltocheckforsingle-modeoperation.
10. Measurethelaseroutputpowerasafunctionofdiodeinjection
current,andplotthepower/currentresponseasinFig.2.1.
Compareagainsttheoriginaldataprovidedwithyourlaser
and if concerned about discrepancies, contact MOGLabs.
11. Switchthecurrentbias(DIPswitch4)backon,andadjustthe
bias to optimise the mode-hop-free scan range.
Thelaser should now be operating with mode-selected feedback
nearthedesiredwavelengthofthediode. Thethresholdcurrent
shouldbesignificantlylowerthanwithoutfeedback(2to5mAfor
standard780nmdiodes). Recordtheoutputpowerandthreshold
characteristics for subsequent reference.