Gentec-EO Beamage-M2 - Manual (Page 21)

Beamage-M 2 User Manual Revision 2.0 21
3.3. “Real Time” Calibration Mode
The “Real Time” Calibration Mode requires two Beamage-3.0 cameras. One camera is mounted on the
Beamage-M2 module to measure the M
2 factor, while the other camera monitors the input laser for a
continuous calibration. This means that if the laser shape changes during the measurement it will automatically
correct the M
2 measurements.
3.3.1. Optical setup
Figure 3-12 Real Time Camera Mode setup with a Standalone Laser
This section will guide you through the necessary optical setup for the M 2 factor measurement of a “Real Time”
Calibration Mode with a standalone laser. The use of an optical table or breadboard is recommended for the
alignment of the optical elements.
1- A dove prism can be used to split the laser signal in two. One optical path will be for the actual M 2
measurement and the other will be for the Beamage-3.0 camera which will monitor the laser.
2- Determine how much attenuation you need on the module to avoid damaging or saturating the CMOS
sensors of both Beamage-3.0 cameras. Please note that the Fabry-Perot reflective glasses in the
Beamage-M2 module offer an ND4.0 built-in attenuation. Optional ND0.5 to ND5.0 attenuators are also
offered. If a greater attenuation is needed to avoid overheating of the optics, additional partially
reflective glasses can be C-mounted on the aperture of the Beamage-M2 module.
3- Fix the converging lens in one of the optical paths created by the dove prism. The lens must be chosen
so that the beam has a Rayleigh length between 50 μm and 6 mm after passing through the lens. The
adjustable distance between the Fabry-Perot etalons allows the measurement of any system using a
lens with focal length equal to or higher than 110 mm. If it is not positioned accurately, it will not be
possible to have the minimum diameter halfway through the series of spots displayed in the software.
To be sure the lens is in the linear propagation regime of the laser, the lens must be placed at least at
three times the Rayleigh length from the laser.