Evolution of a real-time laser M2 measurement system

In 2011, the authors introduced a multispot, real-time ${\mathrm{M2}}^{}$ measurement technology that fulfilled the missing ability of the existing ${\mathrm{M2}}^{}$ measurement systems to dynamically measure thermal lensing in high-power fiber laser systems. Over the next years, the technology has evolved making the technology of $M^2$ measurement compact, easier to use, and more accurate. The traditional $M^2$ measurement technology, being a time-averaged measurement, is incapable of seeing transient changes in a laser system’s $M^2$, let alone thermal lensing. The multispot approach provides an $M^2$ measurement in a single laser pulse or at the frame rate of the pixelated sensor being used. This paper covers the evolution of the multispot ${\mathrm{M2}}^{}$ measurement technology and how it has matured into a state-of-the-art ${\mathrm{M2}}^{}$ measurement tool.