Characterization of general astigmatic beams

Abstract

The well tested and accepted ISO standard 11146 provides the measurement procedures to characterize the propagation properties of stigmatic and simple astigmatic laser beams which are intrinsically symmetric. The beam diameters are defined by the second order moments of the power density distribution which can be measured e.g. with a CCD-camera. In this standard the second order moments are used since the knowledge of these second order moments allows the calculation of the beam properties behind aberration-free optical systems with the well known ABCD-matrices. The new ISO/FDIS 11146-2 provides a new measurement procedure to characterize general astigmatic beams which are characterized by ten independent second order moments of their Wigner distribution. We present experimental results of the characterization of general astigmatic beams which are generated by propagating a simple astigmatic beam through a cylindrical lens which is tilted with respect to the symmetry axis of the beam. These generated general astigmatic beams are characterized according to the new ISO standard ISO/FDIS 11146-2. According to this standard the twist parameter is measured by acquiring two power density distributions in the focal plane of a cylindrical lens which is orientated in horizontally and vertically focusing direction. The twist parameter is given by the difference of these two mixed spatial moments divided by the focal length of the cylindrical lens. We present a possible improvement of this measurement technique by measuring in several planes behind the cylindrical lens. The measured data of the general astigmatic beams and their derived beam properties are presented with a detailed error analysis of the data.