Shack-Hartmann wavefront sensor with high sensitivity by using long focal length microlens array

Abstract

The performance of Shack-Hartmann wavefront sensor (SHWFS) is mainly described by the accuracy, spatial resolution, dynamic range, and sensitivity of the measurement. These factors are particularly affected by the design of the microlens array (MLA). In order to provide a large dynamic range of wavefront measurement, most of the conventional and commercial SHWFS implemented a short focal length lenslet array, which means that the measurement sensitivity is being sacrificed and the accuracy of the wavefront sensor will be degraded. However, it is also critical to detect very small displacement of SHWFS spot in order to reconstruct it into a fine wavefront variation. We fabricated long focal length MLA with various structure arrangement by thermal reflow process with Polydimethysiloxane (PDMS) cover on the glass substrate and implemented them on the image system. A longer focal length will provide high sensitivity in determining the average slope across each lenslet under a given wavefront, and the spatial resolution of the wavefront sensor is increased by the number of lenslets across the detector. The experimental setup consists of the fabricated 245 μm diameter MLA which provides a 5.2 mm long focal distance and is paired with the CMOS as the detector. The observable smallest sensitivity is around wavelength/20 (λ=630nm).

Pantoscopic tilt induced higher order aberrations characterization using Shack Hartmann wave front sensor and comparison with Martin's Rule

“…Hence it is not only important to align the optical components of a SHWFS for the tilt, but also it is important to know the upper limit of the tilt in a given SHWFS. Earlier studies used different focal length lenses in their experiments using SHWFS [18][19][20]. In this work, it stresses the importance of using these lenses without inducing the tilt.…”

Enhancement of wavefront measurement sensitivity in a zonal wavefront sensor without curtailing the sensing speed

“…In order to achieve the highest possible dynamic range, lenslets are designed to have a short focal length and thus the minimal sensitivity. In order to enhance the sensitivity, therefore, a lenslet array with a longer focal length [9] needs to be fabricated. However, the issue of fixed focal length of the lenslet can be resolved by using a liquid crystal based scanning aperture placed in front of a focusing lens followed by the detector array [10].…”