Zonal wavefront sensing using an array of gratings

Abstract

We describe a zonal-wavefront-sensing technique using an array of plane diffraction gratings. A spatially coherent beam, whose wavefront is to be measured, is incident on the array of gratings. The direction of a diffracted beam of a certain diffraction order is a function of the orientation and periodicity of the corresponding grating. Thus, by choosing the orientation and periodicity of each grating appropriately and by having a lens immediately behind the grating array, it is possible to get an array of focal spots. The profile of the incident wavefront can be estimated from the displacements of these focal spots relative to those due to an unaberrated beam. The arrangement makes it possible to increase the separation between two adjacent focal spots corresponding to two nearby gratings without effecting the areas of the gratings. Consequently, a relatively large dynamic range in wavefront measurement can be achieved without compromising the accuracy. With the arrangement it is also possible to use a photodetector array whose outline is independent of the grating array outline. The proposed wavefront-sensing technique is implemented experimentally using a liquid-crystal spatial-light modulator in conjunction with a CCD camera, and the obtained results are presented.

Optical Properties of Multi-Microgratings, Their Replication and Applications

“…An array of circular 1D gratings was also reported for sensing zonal wavefronts [28]. A schematic design of the device is presented in Figure 1.9(a), where light is incident from the left into the micrograting device G and focused by a lens L into the detector D. The micrograting device schematic is shown in Figure 1.9(b).…”

“…The position of the diffracted orders was then monitored for different orders and the wavefront aberration was calculated by angular discrimination. (d) Third order diffracted beams at the detector plane [28].…”

“…The first one was an array of circular zonal plates, with different grating periods inside each circular cell and oriented at different angles using 4x4 cells [28]. An image of the device was used to simulate the diffracted pattern using a Graphical Fourier Transform approach.…”

“…1.9 (a) Schematic design of zonal wavefront device in [28]. (b) Schematic of the 4x4 circular micrograting device.…”

“…(c) First order diffracted beams at the detector plane. (d) Third order diffracted beams at the detector plane [28]. 18…”