High-resolution Shack-Hartmann sensor uses GRIN lens array
Most Shack-Hartmann (S-H) sensors used to measure wavefront distortion depend on refractive microlens arrays, and are able to achieve sampling densities in the range from 1 to 10 lens/mm when the minimum diameter of the lenslets is 100 μm. Unfortunately, these microlenses are difficult to fabricate with lenslet diameters <100 μm and degrade in performance when trying to focus high-refractive-index beams, such as in aqueous environments.
To increase the sampling density to 50 lens/mm and measure wavefront distortion in high-refractive-index environments, scientists at the Institute of Electronic Materials Technology (Warsaw, Poland) and Heriot-Watt University (Edinburgh, Scotland) have replaced the microlens with a graded-index (GRIN) lens array in which each 1-mm-diameter hexagonal lenslet rod is formed in a stack-and-draw process from 7651 hexagonal glass rods with 0.5 mm diameter composed of two different optical materials (low-index silicate glass NC21 and high-index lead-silicate glass F2). Next, 469 of these hexagonal lenslets are stacked and further drawn down into a flat lens array with 318.5 μm diameter and 50-100 μm thickness consisting of the hexagonal core with 20 μm diameter lenslets and external circular cladding. Using the GRIN lens array in a S-H configuration, wavefront distortion was measured by analyzing the minute shifts in the beams refracted from each of the 469 GRIN lenslets through a regularized reconstruction method. Sampling resolution is much higher than in currently available configurations of Shack-Hartmann sensors. Reference: R. Kasztelanic et al., Opt. Express, 25, 3, 1680-1691 (2017).
Gail Overton | Senior Editor (2004-2020)
Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.