96
Revision 00 EN - 01/2021
HP-MSM-HB
35,0(6
22.2.4
Summary
If the laser is pulsing at a high frequency (> 500 Hz) or if the pulses last a long time (> 1ms), it is best to mea-
sure with the
Optim.
option. This makes it possible to vary or optimize the integration time during a caustic
measurement.
For the long pulse duration, choose the attenuation so that the integration time is smaller than the pulse
duration even outside of the focal point.
When the pulse frequency is very high, however, the attenuation must be chosen so that enough laser pulses
are integrated during the measuring cycle. If too few pulses come during an integration time, the number of
photoelectrons will change too much with each pulse. The regulating routines of the LaserDiagnosticsSoft-
ware LDS will then lead to measurements with signal levels that are statistically too high.
It is important to make sure that the integration time is never smaller than the pulse pauses. If this is the
case, it will no longer be possible to perform an untriggered measurement properly with the HP-MSM-HB.
So it sometimes makes sense to set the attenuation so that exactly one pulse is enough to expose the sen-
sor at the focal point. You can then measure a caustic with a fixed delay and an integration time set when the
focus was measured. The dynamic of the CCD sensor (55 dB) is sufficient to measure the entire caustic with
an acceptable S/N ratio.
