VARIABLE SENSITIVITY OF VECTORIAL SHEARING INTERFEROMETER G. Garcia-Torales* b , G. Paez a , M. Strojnik a , J. Villa c , J.L. Flores b . a Centro de Investigaciones en Optica, Loma del Bosque 115, Leon Gto., MX, CP 37000; b Universidad de Guadalajara, Av. Revolución 1500, Guadalajara Jal., MX CP 44840; c Universidad Autónoma de Zacatecas, DSP Laboratory, Zacatecas, Zac., MX CP 98000 ABSTRACT A vectorial shearing interferometer with variable sensitivity based in the rotation of a pair of wedge prisms is discussed. The prism rotations incorporates differential and extended wavefront controlled displacements, combining the advantages of high sensitivity of conventional interferometers and low sensitivity of traditional shearing interferometers. The vectorial shearing interferometer allows the optimization of the measurement parameters for wave reconstruction algorithms. The reliable directional sensitivity of this interferometer has been experimentally demonstrated in spherical and aspherical surfaces. We also show the regularization technique to estimating the wavefront shearing interferometric patterns generated in vectorial shearing interferometry. Keywords: Interferometry, Optical instruments, Optical systems, Optical testing, Aspherics 1. VECTORIAL SHEARING INTERFEROMETER The growing interest in the development of new techniques of fabrication and testing of asymmetrical optical elements is a consequence of the requirement for compactness and lightweight of modern optical devices 1-4 . Asymmetric optical elements frequently replace several traditional components to reduce or eliminate aberrations: one aspherical surface replaces several spherical ones 5, 6 . Unfortunately, their laborious fabrication and testing can become the principal disadvantage 7 . Such components produce intensity patterns with a high fringe density, due to large optical path differences introduced with the available reference components. This often prevents the unique recovery of the phase information due to the formation of moiré patterns. Shearing interferometers are self referencing: they compare the wave front under test with itself. In order to discriminate between rotationally and non rotationally symmetric aberrations, this technique requires at least two intensity patterns with orthogonal shear directions. Several shearing interferometers use a plane parallel plate to displace the wave front in two orthogonal directions 8 11 . Finally, least squares numerical methods are usually employed to fit the wave front polynomial for aberration wavefront reconstruction 12 14 . Figure 1 shows our implementation of the vectorial shearing interferometer based on the Mach Zehnder configuration. Light from a laser source is expanded and filtered before illuminating the optical element under test, in this case a positive lens, producing a collimated beam. The beam splitter BS1 separates the collimated beam in two equal intensity beams, A and B. The wave front A is directed through the shearing system, while the wave front B passes through the compensation system. Both collimated beams preserve their states of polarization. The superposition of the wave fronts A and B, by the action of the beam splitter BS2, generates a modulated interferometric intensity pattern. The image acquisition system, including a focusing lens and a CCD camera, records the interferogram for posterior processing. Shearing and compensation systems consist in a pair of identical prisms individually mounted in a rotary holder, which is perpendicular to the direction of the wavefront propagation. These holders allow continuos variation of the angular position of each prism, 1 and 2 , from 0º to 360º. Each prism of the shearing system can be rotated independently to determine the magnitude and the direction of the displacement of wave front A. Prisms of the compensation system are settled to accomplish the minimum deviation between wave fronts A and B. We define two principal prism positions in order to set the limits of the minimum and maximum deviation wave fronts A and B. Minimum deviation is reached when the top of the first prism is aligned with the bottom of the second prism, e.g., the relative angle between prisms = 180º, e.g. 1 = 0º and 2 = 180º. Maximum deviation is reached when = 0, e.g. 1 = 0º and 2 = 0º. Infrared Spaceborne Remote Sensing XII, edited by Marija Strojnik, Proceedings of SPIE Vol. 5543 (SPIE, Bellingham, WA, 2004) 0277-786X/04/$15 · doi: 10.1117/12.561583 338 DownloadedFrom:http://proceedings.spiedigitallibrary.org/on06/01/2017TermsofUse:http://spiedigitallibrary.org/ss/termsofuse.aspx