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MSM+ HB
I in W/cm²
Fig. 16.4:
Measuring with different integration times
12 – 200 µs:
200 – 400 µs:
200 – 2 ms:
2 – 200 ms:
Fig. 16.4 shows pulsed irradiation. The pulse pauses are 200 µs. The required integration time of the sensor
correlates directly with the intensity of the laser beam.
If it is smaller than the pulse pause as in case 1, statistically there is a maximum of 1 pulse in the
measurement. The probability that a pulse is present during each measurement for integration time control
as well as during the actual measurement is low.
If the optimal integration time falls exactly between the simple and double duration of the pulse pause, there
will always be just one pulse in each measurement (case 2). This is the perfect state for measuring on one
plane. The caustic can also be measured with this setup. Here it is important to make sure that the signal sa-
turation for the measurement in the focus is as high as possible. Only then is it possible to ensure that there
is a sufficient S/N ratio when measuring a plane far outside of the focus.
Case 3 describes the case in which the integration time ranges between the single and tenfold duration of
the pulse pause. Within this range, every pulse is more or less noticeable as a clear signal jump during the
integration time. Integration time control is only possible with quantization. The measuring results often have
a bad S/N ratio or the signal level is too high.
If the integration time increases even more, the signal jumps become flatter. Integration time control operates
quasi continuously (case 4). The laser being measured can now be measured as a cw laser.
The neutral-density filters, which can be inserted into the optical path, make it possible to always work within
the desired range 1 to 4.
In addition, trigger operation is available for the device. Together with the integration time control and a delay
time control, measurements can also be made reliably in case 1.
These four cases can generally be sorted into two groups. Case 1 and 2 must be measured in trigger ope-
ration. Case 4, however, is best measured in quasi-cw operation. Case 3 should be avoided altogether by
choosing a suitable filter.
The diagram in Fig. 16.5 shows a classification of laser beams to be measured with regard to the suitable
operation mode.
Revision 00 EN - 02/2022
∆t in μs
Sporadic measuring of pulses
1 pulse
Quantization noise cause by a varied number of pulses
Virtually continual integration time control
t in μs
113
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