04/02/2008 • Image processing / Optical metrology

M²-Stage for WinCamD

There is an increasing interest to measure the non-dimensional M²-factor in order to rate the quality of a laser beam. This factor is sometimes also named as beampropagation.

The key statement is, that based on the M² factor the beam propagation of a laser beam can be characterised in general and independent on the mode distribution, because it is invariant against transformations by optical components in absence of aberration effects. A perfect Gaussian intensity distribution (TEMoo mode) would give an M² factor of 1. Higher values indicate the appearance of higher modes in the intensity distribution. Such modes do have a significant influence on the divergence of, and the ability to focus the laser beam.

Function principle
The main option of the WinCamD system is the M² stage. The combination of BeamScope and M² option gives the user a very flexible, high resolution scanning system for cw and pulsed lasers with the capability to measure the M² factor according to the ISO standard.

To measure, the scan head needs to be mounted on the linear translation stage. It will be moved through the focal area of any lens suitable to achieve an adequate spot within the scan range of the stage. On each position the beam diameter is measured in one or two axis (as selected). After finishing the scan, the mathematic fit and the calculation of the M² factor is performed by the software. The current ISO standard requests to measure the beam diameter by based on the second moments of the full beam. This calculation is included in the software delivered with the system.

The open setup allows an easy and fast alignment of the system. In contrast to other systems it is not necessary to use a special lens (with respect to size, focal length and coating) in a fixed position, the system only needs to input the current lens parameters and position into the software.

Highlights
  • very flexible setup
  • no limitation with respect to lens parameters and position 
  • measurement speed adjustable (steps, averaging) 
  • adjustable scan range (max. 45 mm) 
  • measurement of the M² factor in 1 or 2 axis 
  • min. step size - 2.5 µm 
  • standard lens (achromatic, 85 mm focal length) incl.
Parameter: Specification
Standard lens (inkl.): Achromat f = 45 mm, 355 nm - 1050 nm
Free Aperture: ø 17.5 m
Scanrange: 45 mm
Step width: 2.5 µm (adjustable)
Software: Average, Nuber of steps, Speed adjustable
Display: 2D or 3D, for X&Y: M², 2Wo, Zo, Zr, Theta, NA
Interface: Export in Systemformat or as Text
Cable: 3 m

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82234 Wessling

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