Improved wavefront estimation accuracy in a programmable grating array based wavefront sensor

Abstract

Shack–Hartmann wavefront sensor (SHWS) is one of the popular zonal wavefront sensor that typically consists of a two-dimensional (2D) array of lenslets and a camera. Another variant of a zonal wavefront sensor is the programmable grating array based wavefront sensor (PGAWS) that replaces the lenslets array of the SHWS with a 2D array of programmable diffraction gratings and a single focusing lens to result in a 2D array of +1 order spots. The ability of a PGAWS to correctly measure the incident wavefront depends on the accuracy with which each +1 order spot centroid position in the camera plane is calculated. However, in practical applications the intensities of the +1 order spots are usually non-uniform and there is presence of higher order spots that lead to erroneous calculation of the centroid position. In the present work, an improved PGAWS is proposed and by exploiting its programmable facility the transmittance function of the grating array is defined to generate an array of uniform intensity +1 order spots with negligible contribution from unwanted higher order spots by breaking them into noise. We present proof-of-concept simulation results that illustrate the generation of uniform intensity +1 order spots and also quantify its uniformity numerically by defining a quality metric. Furthermore, the working of the proposed PGAWS is substantiated through simulation results which demonstrate its accurate wavefront estimation capability in comparison to the conventional PGAWS, in the presence of non-uniform intensity +1 order spots.

An improved programmable grating array based wavefront sensor

“…In the proposed GAWS, 20 the intensity of the +1 order spots can be manipulated by changing the width of the transmittance portion of the diffraction grating, which is also known as the duty cycle (details about the construction of the conventional GAWS can be found elsewhere 4,5 ). The duty cycle of a binary diffraction pattern is defined as the ratio of the opaque or transmittance width (t) to the period of the grating pattern (p), i.e., D = t p .…”

Improvement in wavefront measurement accuracy in grating array-based zonal wavefront sensors by modulating the intensity profile of the incident beam

“…The intensity of the +1 order beam can be manipulated by varying the duty cycle (α shown in figure2 (b)) of the transmittance function. 36 However, without varying the duty cycle, we can also modulate the intensity profile of the incident beam. 27 If we consider a hologram (H(Φ)) where α < π for a normalized intensity, the value of α can be calculated by the Fourier series analysis of the transmittance function of the hologram,…”