What does the M2 specification for a laser mean?

M2 is a measurement of the quality of the beam propagation. It is a ratio of the actual beam propagation over the diffraction limit. It can be used to identify how the beam will change as it travels when compared to a Gaussian beam. The closer the value is to 1, the better the performance of the laser. An M2 value less than or equal to 1.2 is generally considered good performance. The value is useful in determining maximum focused spot sizes and the effects on beam delivery systems.

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