Polytec PSV-500, Hardware Manual

Page: 49 / 109

4-7
4 Making Measurements
Optimal stand-off distance = 141 mm + (n · l) mm
This means the optimal stand-off distances are: 141 mm, 345 mm, 549 mm,
753 mm, 957 mm, etc.
4.3.3 Optimal Stand-Off Distances with PSV-A-560 CoherenceOptimizer (optional)
The laser mode only reaches a constant state once the laser temperature is
constant. Without the CoherenceOptimizer, this temperature equilibrium is
only reached several hours after switching on the laser. It is impossible to
predict whether a particularly advantageous state is reached with one strongly
dominant laser mode, or alternatively, a particularly disadvantageous state is
reached with two modes of equal strength. The slightest temperature
fluctuations can already change the state of the laser mode.
The CoherenceOptimizer is a system to stabilize the laser modes. It adjusts
the laser resonator to a constant length so that a strongly dominant laser
mode is formed. This minimizes signal level drops in the visibility minimum. If
in the software the CoherenceOptimizer is displayed as being stable, the
signal level hardly varies over the stand-off distance. This means that with the
CoherenceOptimizer it is no longer necessary to position the object at the
stand-off distance of a visibility maximum. In addition to that, the time that the
scanning head takes to warm-up is also reduced.
The CoherenceOptimizer can cause interferences at a frequency of 610 Hz
and harmonics. Switch off the CoherenceOptimizer if this interferences affect
the measurement result. For measurements with CoherenceOptimizer being
switched off, pay attention to the optimal stand-off distances in
SECTION
4.3.2.
n … 0, 1, 2, …
l … 204 mm ± 1 mm