MOGlabs CEF, Manual

Page: 33 / 60

4.2 Filter adjustment
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6. Increase SPAN until a mode-hop is evident. If using absorption spec-
troscopy to monitor the laser wavelength, it can be helpful to observe
the derivative, for example the demodulated error signal ( CHAN BError
on a MOGL abs DLC ).
The mode hop should be at one edge of the scan; if so, adjust FRE-
QUENCY so that the scan no longer ’clips’ this mode hop (i.e. the scan
is free of mode hops), and continue adjusting in the same direction
until a mode hop is observed on the other edge of the scan.
7. Adjust FREQUENCY to the mid-point between the two extremes.
8. Increase SPAN and adjust FREQUENCY mode hops are evident at both
edges of the scan.
9. Adjust diode CURRENT by small amounts to suppress the mode hops.
Increase SPAN and adjust CURRENT and FREQUENCY until the mode
hops cannot be suppressed.
10. Adjust the BIAS trimpot to suppress the mode hops. Repeat the steps
above: increase SPAN , adjust CURRENT , FREQUENCY and BIAS , and
repeat until no further improvements can be made.
11. If the MHFR is substantially less than expected (refer to the factory
test report), it may be helpful to change to a different intrinsic diode
mode by increasing or decreasing
CURRENT
. Alternately rotate the
filter slightly to alter the net gain so that one cavity mode has higher
gain than those adjacent.
4.2 Filter adjustment
The primary control of wavelength is the filter rotation angle, which can
be adjusted while the laser is operational. A MOGL abs Fizeau wavemeter
or high-resolution spectrometer is almost essential, though with patience
it is possible to find an atomic resonance by carefully adjusting the filter
angle while scanning the laser.