A direct comparison between a MEMS deformable mirror and a liquid crystal spatial light modulator in signal-based wavefront sensing

Aberrations degrade the performance of optical systems in terms of resolution and signal-to-noise ratio. This work explores the feasibility of a signal-based wavefront sensor, which employs a search algorithm to estimate Zernike coefficients of given aberrations. The search algorithm was supported by Gaussian interpolation. The performance of two different reflective wavefront correctors, a deformable mirror and a spatial light modulator in signal-based wavefront sensing, was compared under identical conditions. The aberrations were introduced by using another identical high resolution reflecting spatial light modulator. The performance was quantified using the Strehl ratio, which was estimated from simultaneously acquired Hartmann-Shack measurements of Zernike coefficients. We find that the spatial light modulator can be a good alternative to the deformable mirror in terms of dynamic range and sensitivity, when speed is not a limiting factor. Distinct advantages of the spatial light modulator are high number of pixels and a larger active area

Computational lens for the near field

A method is presented to reconstruct the structure of a scattering object from data acquired with a photon scanning tunneling microscope. The data may be understood to form a Gabor type near-field hologram and are obtained at a distance from the sample where the field is defocused and normally uninterpretable. Object structure is obtained by the solution of the inverse scattering problem within the accuracy of a perturbative, two-dimensional model of the object

Virtual pyramid wavefront sensor for phase unwrapping

5 pags., 7 figs. ; OCIS codes: (010.1080) Active or adaptive optics; (010.7350) Wave-front sensing; (120.5050) Phase measurement; (280.4788) Optical sensing and sensors; (080.1010) Aberrations (global); (120.3180) InterferometryNoise affects wavefront reconstruction from wrapped phase data. A novel method of phase unwrapping is proposed with the help of a virtual pyramid wavefront sensor. The method was tested on noisy wrapped phase images obtained experimentally with a digital phase-shifting point diffraction interferometer. The virtuality of the pyramid wavefront sensor allows easy tuning of the pyramid apex angle and modulation amplitude. It is shown that an optimal modulation amplitude obtained by monitoring the Strehl ratio helps in achieving better accuracy. Through simulation studies and iterative estimation, it is shown that the virtual pyramid wavefront sensor is robust to random noise. © 2016 Optical Society of AmericaConsejería de Educación, Juventud y Deporte of Comunidad de Madrid and the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7) (FP7/2007-2013, REA n°291820) to V. A.; Science Foundation Ireland (SFI) (07/SK/B1239a, 08/ IN.1/B2053);University College Dublin (UCD) (seed funding: SF665) to B. V.; European Research Council (ERC) (ERC- 2011-AdG 294099); Spanish Government Grant (FIS2014- 56643-R) to S. M.Peer Reviewe

Direct visualization of evanescent optical waves

The existence of evanescent optical waves is usually demonstrated by the observation of transmitted light in frustrated total-internal-reflection experiments that make use of two closely spaced prisms. The main characteristic of a monochromatic evanescent plane wave is the exponential decay of its amplitude in the direction perpendicular to its surface of generation. This decay, however, is not what is seen in the usual experiments when the gap between the prisms is small. Only when the gap is sufficiently large does it gradually approach the exponential dependence. We use a different technique that uses a local probe to reveal the presence of an evanescent wave. The results come closer to the ideal of the exponential decay of the wave amplitude, and the presence of the evanescent wave can be seen directly, making it a suitable demonstration for pedagogical purposes. © 2003 American Association of Physics Teachers

Blind deconvolution for high-resolution confocal scanning laser ophthalmoscopy

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