20 Chapter 4. Troubleshooting
4.2 Filter adjustment
This section contains mechanical details that apply only to serial num-
bers A323xxxxx and above. For older cateye lasers, refer to the appro-
priate manual prior to version 2.01.
Theprimarycontrolofwavelengthisthefilterrotationangle,whichcan
be adjustedwhile thelaser isoperational.A MOGLabsFizeau wavemeter
or high-resolutionspectrometerisalmostessential, thoughwithpatience
it ispossible to findan atomicresonance bycarefullyadjusting thefilter
angle while scanning the laser.
WARNING: Ifthediode is powered on, ensure thatthefilter is never
perpendiculartothelaseraxis(i.e. filterangle0
◦
,whenfilternotchon
spindle is parallel to optical axis in figure 3.1). The filter is a highly
reflectivemirrorthatwillback-reflectlightintothediode,whichcancause
catastrophic damage.
To change the wavelength:
1. Setthelasercurrentsothattheoutputpowerissufficient,taking
care to ensure that the internal cavity power is below the maximum
rated for the bare diode i.e. without feedback (see figure 2.1).
For adjustments of greater than 1nm:
2. Unlockthe filterso that itcan rotate,by turningthe spindle-clamp
lock screw anti-clockwise, for example one full turn.
3. Rotatethe filterassemblyspindleusinganallenkeyorhexball
driver inthe hexsocket inthecentre ofthe shaft,makingsurethat
the notch does not align at 0
◦
to the optical axis.
4. Lock the spindle-clamp.
5. Optionally adjustthe finediodefocustooptimise thelasing thresh-
old, and subsequently make corrections to the output collimation
lens as necessary to recollimate the output (see §4.3).
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