Performance measurement of adaptive optics system based on Strehl ratio

In this article, a method for measuring the performance of adaptive optics (AO) systems is designed and validated by experiments. The Strehl ratio (SR) which is based on the target images is used to evaluate the performance quantitatively because it relates to the effect of AO correction directly. In the calculation of the SR, to avoid energy scaling in the diffraction-limited point spread function, an algorithm based on the integral of the optical transfer function (OTF) is proposed. Then, a 97-element AO system is established to validate this method, and a white-light fiber source is used as a point-like target. To simulate the practical conditions which influence the performance of the AO system, targets of different brightness are simulated in terms of different signal-to-noise ratios (SNRs) of the Shack-Hartmann (SH), and atmospheric turbulence is simulated in terms of the Fried's coherence length and the Greenwood's frequency. Finally, two experiments are conducted in which the SR of different simulated conditions are measured. The results of the experiments show that for a moderate SNR of SH the experimenting AO system is capable of closed-loop wavefront correction when the Fried's coherence length is larger than 5cm and the Greenwood's frequency is lower than 60 Hz. The results also show that the performance of AO is susceptible to the SNR of SH. The experiments validates the effectiveness of this method.