Specifications

4. Operation
Normaloperationofthelaserisusuallyamatterofadjustingthe
filterrotationangletoselectthecorrectwavelength,andadjust-
ing thepiezo offset,diode injectioncurrent andbias toachieve the
maximum possible mode-hop free scan.
4.1 Wavelength
Theprimarycontrol ofwavelengthis thefilterrotation angle,which
canbeadjustedwhilethelaserisoperational. Awavemeter [7],
high-resolutionspectrometer,orsimilarisalmostessential,although
with patience it ispossible to find an atomic referencebycarefully
adjusting the filter angle while scanning the laser.
The filter transmission wavelength shifts with rotation according to
λ(θ)=λ
0
s
1−

sin
(
θ
)
n
eff

2
(4.1.1)
whereθ istheangleofincidence,λ
0
isthefilterwavelengthatnor-
mal incidenceandn
eff
= 2.13forp-polarization. The sensitivityto
rotationofthefinetangentialwavelengthadjustmentscrew(labelled
λ in figure) is about 0.5nm per turn.
Setthelasercurrentsothattheoutputpowerissufficient,taking
care to ensurethat the internalcavity power is belowthe maximum
ratedforthediode(seeFig.2.1). Thenchangethefilterangleto
adjustthewavelength. Thelaserwillhopbetweenexternalcavity
modes, asthewavelengthisadjusted, throughcyclesofdimand
brightoutput. Adjusttheangletooneofthebrightmodesnearest
the optimumwavelength,andthenadjustthelasercurrent andthe
piezo voltage to achieve the exact wavelength required.
15