Physical limitations in fast measuring and adaptive phase systems

Abstract

Limitations on the design of high-speed systems intended for measuring the optical wave phase and its adaptive control in a turbulent atmosphere are analyzed in the present work. While faster system performance can be beneficial, simply striving for speed without considering other factors can lead to unintended negative consequences. In particular, increasing the operating frequency of a wavefront sensor (WFS) can introduce errors in measured phase fluctuations, because the WFS signal dependence on the amplitude of fluctuations can be affected by the increased frequency, potentially leading to inaccuracies in the measurement of phase changes. For a number of applications, this is primarily caused by the limited photon flux and measurement accuracy of the wavefront sensor. The present work is focused on understanding how atmospheric turbulence affects the phase of light waves and how to accurately measure these effects for application in adaptive optics. A need is revealed to analyze how phase fluctuations, caused by the atmospheric turbulence, change over time. It has been found that the choice of the working WFS frequency depends not only on the parameters of the sensor itself and primarily on the accuracy of its performance, but also on the state of turbulence on atmospheric paths. Therefore, no matter how fast the corrective flexible mirrors in adaptive optics systems are, they need to be given time to work. As a result, inaccurate estimations of phase fluctuations and Zernike polynomial behavior arise at high spatial frequencies due to the influence of the inner scale of turbulence, even when the turbulent intensity fluctuations are weak.