DataRay Blog

M² and High-order Modes

M² is a measurement that was originally designed to determine the quality of a real beam in comparison to a theoretically perfect fundamental mode Gaussian beam (Siegman 1990). Although many lasers are designed to output a fundamental mode Gaussian beam, imperfections and/or cavity design in the laser will often cause superimposed higher-order transverse modes. M² provides an excellent metric for determining the higher-order mode content. In his original paper introducing M², Siegman gives mathematical expressions for the theoretical value of M² based on the weighted content of the various modes in a beam. In this blog post, we will programmatically generate Gaussian beams with multi-mode content and then analyze the M² value of these artificial beams calculated by the DataRay software in order to confirm the accuracy of our algorithms.

M² Measurement

As leaders in the laser beam profiling business, we have worked with M² for decades. In this blog post we discuss M², when to use it, and the way it is measured. M² is a very useful measurement for a certain subset of laser beams—those that are predominately Gaussian—and determines how tightly an actual laser beam can be focused in comparison to a theoretically perfect Gaussian beam. Sometimes, customers wish to use M² as a laser beam metric, even when it isn't the most appropriate metric to use for their application. Even if M² isn't the right diagnostic metric for your beam, we would love to work with you and design a custom metric to assess the quality of your beam.