M² measurements, as defined by the ISO 11146-1:1996 standard, have historically presented significant challenges, even for experienced practitioners. Measurement variability exceeding 10% for the same instrument applied to the same laser is frequently observed, primarily due to factors such as misalignment, time-averaged beam motion, complex attenuation methods involving variable neutral density filters, and sensor-dependent variations. Additionally, the experimental setup can require several hours, while individual measurements may take several minutes to complete.

Ideally, determining a laser's M² value should be as straightforward as measuring its power: aligning the laser to the instrument, initiating a self-calibration routine, and acquiring the measurement. In 2017, the authors implemented a self-calibration technique for a novel real-time M² measurement system. While theoretically sound, this approach was initially limited in accuracy due to opto-mechanical tolerance constraints that were not easily mitigated.

By refining the opto-mechanical design, the system now achieves consistent, accurate calibration, enabling real-time M² measurement. Improved mechanical referencing, combined with existing sensor data and a simple ray-tracing technique, allows for precise determination of etalon spacing through data deconvolution. This advancement eliminates the need for separate, time-intensive calibration procedures. As a result, critical calibration data can now be obtained within fractions of a second, requiring no manual intervention.