Improvements to the modal holographic wavefront sensor

Abstract

The Zernike coefficients of a light wavefront can be calculated directly by intensity ratios of pairs of spots in the reconstructed image plane of a holographic wavefront sensor (HWFS). However, the response curve of the HWFS heavily depends on the position and size of the detector for each spot and the distortions introduced by other aberrations. In this paper, we propose a method to measure the intensity of each spot by setting a threshold to select effective pixels and using the weighted average intensity within a selected window. Compared with using the integral intensity over a small window for each spot, we show through a numerical simulation that the proposed method reduces the dependency of the HWFS's response curve on the selection of the detector window. We also recorded a HWFS on a holographic plate using a blue laser and demonstrated its capability to detect the strength of encoded Zernike terms in an aberrated beam.

Analysis of HolographicWavefront Sensing Performance for xtended Sources

“…For the characterization of the HWFS, we analyzed the outcome of the response of the available Zernike modes in our simulated HWFS to a single Zernike order as the input wavefront aberration. For every input Zernike mode, the input strength of the wavefront has been varied from a value of minus one to the maximum value of plus one, obtaining response curves similar to those found by Kong et al [4]. A linear response has been taken as the ideal system response.…”

“…After a Fourier transforming lens, the intensity of each Zernike mode is recorded by a detector. The estimation of the measured Zernike strength is given by computing the difference between the positive and negative intensities, as described in [4].…”

Roadmap on holography

“…The use of several separate channels with holograms filtering only one of the Zernike modes in the WFS is impractical, since in this case the sensor becomes bulky and the intensity of the radiation incident on each of the holographic elements decreases (inversely proportional to the square of the number of channels). Therefore, the desire of researchers to use WFS with multiplex holograms [162][163][164][165][166][167][168][169][170] is justified.…”

“…This solution is suitable only for AO systems with zonal corrector. The effect of cross-modulation noise can be reduced by optimizing the design of the filter hologram, the size of apertures and the position of photodetectors and the number of recorded Zernike modes [167,168].…”