High laser power levels combined with increasing beam quality bring optics performance into focus. The subject of
optics performance is a hot topic, but lack of a common nomenclature, as well as of proper measurements, makes the
situation confusing. This paper will introduce a nomenclature for comparing the performance of different types of optics.
Further, the paper will present a test setup for characterizing optics, along with test results for different optics materials
and designs. The main influence of high power levels on optics is a focal shift along the optical axis. In industrial
applications, this might influence the performance of the process, especially if the focal shift is in the range of the
Rayleigh length. In the test setup that is to be presented, the optics are exposed to a high power beam, and a pilot beam is
used for measuring the change in focal position. For a proper description of optics performance, the laser beam
parameters should not influence the measured results. In the nomenclature that will be presented, the performance is
related to the Rayleigh length for a fundamental mode beam. The performance of optics when used with multimode
beams will be presented.