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Angular coordinate error testing of circular writing laser system using Fizeau interferometer

Diffractive optical elements (DOE) with an arbitrary topology are widely used in various fields of modern science and technology. Our paper is dedicated to diffractive optics, which is produced by circular laser writing on CLWS-300. In the process of fabrication of diffractive element, a pre-calculated pattern is written on the optical substrate. During this process, writing errors occur that can introduce distortions into the wavefront generated by diffractive optical element. The error of the angular coordinate can make the most significant contribution to the total error. In addition, this type of error is the most difficult to control and correct. In this paper, we propose a method for measuring the angular coordinate error of the circular laser writing systems based on laser interferometry. The method includes writing special test samples and their subsequent control using a conventional Fizeau interferometer. The angular coordinate error is calculated from the phase map. This method allows detecting errors of the angular coordinates up to 1-2 ang. sec. The test pattern can also be written on the same substrate within a single fabrication process with main pattern. This allows certification and quality control of the fabricated diffractive optical element. In addition, laser writing system can be periodically tested to verify that angular coordinate error is within acceptable limits. The method described in article can be extended to any writing system operating in the polar coordinate system.