MOGlabs CEF, Руководство пользователя

Страница: 35 / 60

4.3 Threshold optimisation
21
9. Once the laser is operating near the desired wavelength, adjust the
diode current and the piezo voltage to achieve the exact wavelength
required. If the CURRENT adjustment has shifted the wavelength to a
mode further away from the desired wavelength, use the fine screw
adjustment method to correct the wavelength.
The filter transmission wavelength shifts with rotation according to
λ
(
θ
) =
λ
0
s
1
− sin(
θ
)
n
eff
2
(4.2.1)
where
θ
is the angle of incidence,
λ
0
is the filter wavelength at normal
incidence and
n
eff
≈
1
.
7 is an effective refractive index. The sensitivity
to rotation of the fine tangential wavelength adjustment screw is about
0.5 nm to 1 nm per turn.
4.3 Threshold optimisation
The lasing threshold, at which the overall gain exceeds losses, should be as
low as possible to maximise the output power and also the scan range and
frequency stability. The lowest threshold is achieved by optimising the
focus of the laser diode collimation lens and the cateye lens (see fig. 4.1).
Set the diode current just below the threshold value specified in the laser
test report, and then adjust the cateye lens focus until the output suddenly
flashes brightly. Repeat until the minimum threshold current is obtained.
25mm
Lens tube Cateye Recollimator
Figure 4.1:
Arrangement of lens tube and cateye reflector for adjustment of focus
of cateye.