Novel method for measuring beam parameter product and M-square

The majority of methods available for measuring the M-square or the beam parameter product of a laser employ a time averaging technique based upon the ISO 11146-1 beam metric standard. In the ISO standard five points must be measured within the first Rayleigh range to establish the beam waist and another five points measured beyond the second Rayleigh range to obtain the asymptote from the corresponding hyperbolic fit of the minimum ten data points measured. Other real time, i.e., instantaneous M-square methods exist but do not fully comply with the ISO 11146-1 standard to the exact letter of the document. One measurement technique is able to view three Rayleigh lengths in real time but due to gain and area limitations of the sensor, the third Rayleigh range is hard to measure to the full extent of the ISO standard or only can be under limited conditions. It is therefore desirable to have a technique that complies with the ISO standard and provide real time M-square or beam parameter product values. We present a technique that simultaneously measures outside the second Rayleigh range while at the same time measure the first Rayleigh range where the gain of the two regions are optimized and there is sufficient area available on the sensor to comply with the ISO standard.