Optical wavefront sensor based on sub-wavelength metallicstructures

摘要

Lateral shearing interferometers (LSIs) are efficient tools for optical analysis. They allow classical optical wave-front aberrations measurements as well as the precise evaluation of abrupt steps. The basic element of an LSIis the transmittance grating, which diffracts a number of orders (two in the case of a mono-dimensional LSI,ideally three or four non coplanar orders in the case of bi-dimensional LSI). This brings the need for specificallydesigned transmittance gratings. For instance, a mono-dimensional LSI needs a sinusoidal-shaped transmittance,since its Fourier transform carries exactly 2 orders. Such transmittances are however either impossible or at leastextremely costly to design using classical macroscopic techniques, mainly because the usual thin film depositiontechniques require several technological steps, in order to get the desired light filtering effect.Given these constraints, we made use of sub-wavelength structures in order to build a new class of LSI. Theyare made of sub-wavelength lamellar metallic gratings specifically designed for the mid-infrared, and allow theprecise coding of the desired transmission shape all over the LSI grating.