Strehl ratio and optimum focus of high-numerical-aperture beamsAugustus J.E.M. Janssen, Sven van Haver, Joseph J.M. Braat and Peter DirksenJ. Eur. Opt. Soc.-Rapid Publ., 2 (2007) 07008DOI: https://doi.org/10.2971/jeos.2007.07008
