Specifications

3.2 Initial diode test 11
distance.
9. Rotatethecollimationassemblyandadjustthealignmentscrews
until the beam remains reasonably well on-axis.
10. Tighten the retaining ring (hard) andre-check that the diode
remains aligned.
11. Focusthecollimationlenssuchthatthelaserfocusestoaspot
atsomesignificantdistance,morethan4m.Thelaserstability
andmodehopfreerangecanbebetterifthelaseroutputis
weakly converging [6].
3.2 Initial diode test
1. Inspect the beam profile for diffraction fringes. If the lens
has been screwed intoofar and made contact withthe diode
(particularlyfor5.6mmdiodes),thelenscanbecomescratched
orstressed,leadingtopoorperformance. Fringescanbean
indicationof suchscratches(oranindication ofapoor diode).
2. OntheMOGLabsDLCcontroller,makesureDIPswitch4(Bias)
is OFF, the span is setto zero (fullyanti-clockwise), andthe
frequencyknobisatzero(middleofrange; setthedisplay
selector to Frequency and adjust to zero volts).
3. Measurethepower/current(LI)curveforthebarecollimated
diode.This provides auseful benchmark forcomparison when
optimising the threshold lowering with feedback.
3.3 Orientation and polarisation of the output beam
Theoutput from the diode is a widely diverging elliptical beam,
normallyTEpolarised;thatis,withpolarisationparalleltotheshort
(minor) axisof the ellipse.Thefilter performance istypically better
inp-polarisation; thatis, withpolarisationintheplaneof reflection