Online measurement of the optical aberrations of a thin-disk laser active medium using the Fourier domain multiplexing method

Abstract

We present an interferometric scheme for the measurement of the deformation of a thin-disk laser active medium with visible light as the probe beam. The disk has a small wedge angle, and the coatings on both of its sides have appreciable reflectance for visible light that prevents using a standard interferometric profilometry procedure. The method that can acquire data in a video rate is based on the interference of three beams, two beams reflected from both sides of the disk and one the reference beam of the interferometer. To obtain the phase variations caused by the deformation of the disk, a Fourier domain multiplexing method has been utilized. The optical setup was designed in such a manner that these three beams were separated in the Fourier domain. The measured data for different deformation profiles of the disk well agree with those obtained with profilometry with an IR probe beam. This method is a fast and simple method since only a single shot in a CCD sensor is required to acquire the morphology of the active medium in thin-disk lasers.