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M² Measurement & Analysis

M², or beam quality factor, is a dimensionless parameter that characterizes the degree of imperfection of a real-world laser beam. The lower the value of M², the more tightly the beam can be focused to a small spot. A theoretical perfect TEM₀₀ beam has an M² value of 1. In reality, however, no laser beam is perfect; limitations of the laser cavity, the lasing medium, and/or the output/ancillary optics, etc., mean that real-world beams are not the diffraction-limited, Gaussian profile, pure TEM₀₀ mode described in textbooks. Complex beams contain multiple mode contributions that increase M². Even a "good" laboratory HeNe laser has an M² of around 1.05 to 1.2.

Best Products for ISO 11146 Compliant M² Measurement

DataRay offers a wide variety of beam profilers that can measure M². These include beam profiling cameras and the Beam’R2 when mounted on an M2DU translation stage, with automated M² measurements in the DataRay software.

The full-featured DataRay software also supports manual M² measurements with when any of our instruments are mounted on a third-party translation stage (with the user entering the sequential stage positions).

It's important to note that measuring M² on a translation stage requires an appropriate lens assembly for beams that are not already focused to measurable size (with enough working distance).

Optimal Lens Selection

Use this Excel spreadsheet to model your M² measurement and help ensure you choose the correct lens assembly.

Figure 1: Results of an automated M² measurement using a WinCamD series camera and M2DU-50 stage

Additionally, relative M² measurements (with lower absolute accuracy) can be made in real-time using the BeamMap2 multiple Z plane scanning slit beam profiler. This can be a great option for quick M² optimization.

Figure 2: The real-time relative M² curve calculated by a BeamMap2

If you’re unsure which product is most suitable for your application or have the need for something custom, please contact us.

Have questions or need help identifying the right solution for your application?

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