To provide an accurate calculation of M², it is essential to make at least five measurements in the focused beam waist region and at least five measurements in the far field, two Rayleigh ranges away from the waist area. The multiple measurements ensure that the minimum beam width is found. In addition, multiple measurements enable a "curve fit" that improves the accuracy of the calculation by minimizing measurement error at any single point. An accurate calculation of M² is made by using the data from the multiple beam width measurements at known distances from a lens, coupled with the known characteristics of the focusing lens.
Having discussed the importance and complexity of the M² measurement, it becomes apparent that optimizing its measurement within the end-of-one line testing is a decisive factor in terms of time savings and general process optimization. To facilitate the process and accurately deliver M², MKS offers the Ophir BeamSquared beam profiler. This compact tool measures the propagation characteristics of CW and pulsed laser systems from the UV to NIR to Telecom wavelengths, fully automated. Additionally, wavelengths above 1.8 microns, including CO2 and terahertz, can be measured in manual mode (a bench set-up; without the automated optical train) with a Pyrocam IV or IIIHR.
The main advantage of Ophir BeamSquared is that it delivers the quality parameter of the laser beam in less than a minute. Compared to its predecessor, the widely used Ophir M2-200, which has been the industry standard for years, the system is 10 to 20 times faster. The beam enters the measurement device and by using several mirrors inside of it, a long beam path is created along which the beam profile can be measured almost in real time. In combination with the patented Ultracal™ Calibration algorithm, Ophir BeamSquared delivers fast and highly accurate ISO 11146 compliant beam propagation characteristics in both the X and Y axes for display parameters such as:
Waist diameters Full angle divergences Waist locations Rayleigh lengths M² or K and BPP factors Astigmatism Asymmetry