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8
to check the device indicator, which should be at the middle position when an
equilibrium has been reached. To allow a complete stabilisation and find a
precise stable condition, check again the transmission after 20-
25’: if
decreased, adjust again the set-point knob. By repeating this procedure 2 or 3
times, a precise tuning of the transmission maximum will be obtained. The user
could also eventually choose to lock the knob into position, using the knob stop
lever.
The instrument transmission stability in time will depend on the temperature
stability of the etalon. A relevant change in the room temperature or in the
convection efficiency with respect to first optimization can negatively affect the
performance; for this reason, it is advisable to use the TCF in a stable
temperature environment. Place the device as far as possible from heat sources
and heat sinks, and far from ventilation sources like fans and windows.
Stability tests performed at production indicate a maximum decrease up to 2%
of the optimized transmittance when temperature stays within ± 1°C from the
optimized conditions. The loss of performance is expected to increase to 5%
with changes of temperature of ± 2°C.
Stabilised filter version (TCF-2) operation
The stabiliser optimises the output of the TCF, allowing increased tolerance
against small changes in room temperature and laser frequency. This will
greatly reduce the need of manual set point adjustments. The stabiliser unit
should be mounted and connected to the TCF before switching it on.
At first installation, keep the stabiliser off (switch lever in the lower position) and
get as close as possible to the maximum using the knob.
When the stabiliser is powered on, independently by the switch position, it will
remain idle (with LED off) for about 8 minutes. This delay is useful to allow the
TCF to reach the set point determined by the knob position after power up. After
this start-up delay, the stabiliser will react immediately to the switch and will
start to operate if the lever is in the top position. When the stabiliser is active,
a very slow sinusoidal modulation of the TCF head temperature will take place,
and the laser power output will be driven to maximum. When the maximum is
reached, the effect of the modulation on the light output will be negligible.
The efficiency of the stabiliser is lower when the set point is close to the limits
of the TCF scale (i.e. very hot or very cold). In these conditions, the time
required to optimise the output is longer: it is thus advisable to use a set point
close to room temperature.
If the laser beam is switched off, the TCF stabiliser should be also turned off:
the stabiliser will be fooled by a sudden drop of the laser power, and will require
time to stabilise again.
