Abstract

It is often important to estimate the margin of improvement of a given laser performance, e.g. for evaluating if the ratio "expected progress" to "effort and cost" is convenient. Considering the laser irradiance, it is usually improved by reducing the laser beam divergence rather than increasing the laser beam power. However, when the laser users want to know how far the laser beam divergence is from its diffraction limit, that is, how much is the 'Time Diffraction Limit number" (TDL) of their lasers, they cannot directly refer to the widely used Siegman-M² or to the ISO K factors. This is because these parameters normalize both the actual beam quality and divergence to the ideal pure gaussian beam. As a consequence, whenever the laser intensity distribution is far from the gaussian-like shape (e.g. high peak-power laser beams), the equivalence TDL = M² can be considered as an improper use of the beam quality factor M²

© 1996 Optical Society of America