4.3 Threshold optimisation 21
For adjustments of less than 1nm:
6. Checkthatthespring-plungerisengagedbutnotlockedagainstthe
brassarmofthespindleclamp. Thatis,thepinshouldbevisibly
protrudingfrom the spring-plungerscrew, and touchingthe brass
arm.
7. Adjustthefilterangleusingthefinethreadλ adjustscrew,acting
against the spring-loaded plunger opposite to the λ adjust screw.
8. Thelaser willhopbetweenexternalcavitymodesasthewavelength
is adjusted, through cycles of dim and bright output.
9. It maybenecessaryto adjustthespringplunger, sothat pressure is
maintainedonthebrassarmofthespindleclamp,withoutlocking
completely.
10. Once the laser is operatingnear the desired wavelength,adjust the
diodecurrentandthepiezovoltagetoachievetheexactwavelength
required.IftheCURRENTadjustmenthasshiftedthewavelengthtoa
modefurtherawayfromthedesiredwavelength,usethefinescrew
adjustment method to correct the wavelength.
The filter transmission wavelength variation with angle is approximately
λ(θ)=λ
0
s
1−
sin
(
θ
)
n
eff
2
(4.2.1)
whereθ istheangleofincidence,λ
0
isthefilterwavelengthatnormal
incidenceandn
eff
≈ 1.7isaneffectiverefractiveindex. Thesensitivity
torotationofthefinetangentialwavelengthadjustmentscrewisabout
0.5nm to 1nm per turn.
4.3 Threshold optimisation
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.
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