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MSM+ HB
9.8
Automatic caustic measurement
In the Automatic caustic measuring mode, only press the start button to automatically determine a caustic.
The centre axis position is preset as the z position. The default setting for the number of measuring planes is
21. The z-range as well as all other required settings are determined and adjusted automatically. In addition,
advanced settings can be applied.
According to ISO 11146-1, at least 10 planes shall be measured. Approximately half of the measurements
shall be distributed within one Rayleigh length on either side of the focus, and approximately half of them
shall be distributed beyond two Rayleigh lengths from the focus.
For two reasons, an odd number of measuring planes makes it more likely that the focal plane will be measu-
red. First, the LaserDiagnosticsSoftware LDS always sets the spacing between the measuring planes equal.
Second, the measuring range along the z-axis is almost always symmetrical around the focus. We recom-
mend measuring at least 21 planes within 6 Rayleigh lengths.
By means of the variable integration time control, not only cw lasers but also pulsed lasers can be measured
in quasi-cw operation. An exception are, for example, laser beams with a very low pulse frequency. Trigger
operation is available for measuring such beams. If this is enabled, the device only measures within defined
time periods. The laser pulse or the corresponding trigger signal marks the beginning of such a period and
the (freely adjustable) integration time marks its end. A measurement can be triggered internally or externally.
Internal signals are triggered by the photodiode integrated in the device. Externally triggered signals enter the
device via a BNC socket. For detailed information on the measurement of pulsed laser beams and the trigger
operation, please refer to chapter 16.3 on page 110.
9.8.1
Configure settings
1.
Click on the Settings tab.
2.
Maintain the options according to the
explanations in the following table.
Option
z-Position in mm
Parking position after caustic
Power P in W *
Tab. 9.9:
Options in the Device control > Settings tab of the Automatic caustic measuring mode
Revision 00 EN - 02/2022
Explanation
The centre axis position is selected as the default setting.
Use one of the following options to set the initial z-position for the pre-
caustic measurement:
X Enter a value in the input field.
X Use the slider below the input field.
X In the drop-down list, select the parking position to which the came-
ra housing will be moved after the caustic measurement.
You can select from the following options:
•
Focus: The camera housing is moved back to the position of the
determined beam focus.
•
Start position: The camera housing is moved back to the start
position.
•
Final position: The camera housing remains in the final position.
The selected position is also the start position for the pre-caustic
measurement of the next measurement (unless you enter a different
value in the z-Position in mm field).
To calculate the power density, the laser power used must be entered.
Otherwise, the measured amplitudes are given directly in counts.
X Enter the laser power used during measurement.
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