Article | January 31, 2013

M2 Beam Propagation – Why So Many Different Approaches To Measurement Instrumentation?

Source: Ophir Photonics
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By Allen Cary, Director of Marketing, Ophir-Spiricon

Measuring the propagation parameters of a laser beam is an important method of understanding the quality of the laser beam and predicting its performance for various laser applications. For this reason, it is one of the major specifications required by laser users and reported by laser manufacturers. Ophir-Spiricon has been a leader in providing instruments dedicated to this important measurement. There are currently three different instruments available under the Spiricon and Photon brands, and in this article we will explain the differences between them and the reasons for these different approaches to making this measurement. Hopefully, this will assist you in deciding which approach is best for your laser and laser application.

The M2 Beam propagation measurement is made by observing how a laser beam behaves when focused with a lens. The ISO 11142 protocol calls for measurements to be made along the z-axis of a beam, both around the waist formed by the lens and additionally at positions at least two Rayleigh ranges away from the waist. At least 5 beam measurements are made at the waist and 5 more at the far field positions. From these measurements a curve fit determines the M2 value. A perfect Gaussian TEM00 laser beam will have an M2 value of 1.