A new technique for high resolution wavefront sensing has been introduced. It is based on the Optical Differentiation
wavefront sensor, however its application has required the development of a diffractive element that provides four or
five copies of the original wavefront. It some aspect the result is similar to that provide by the Pyramid sensor although
from a theoretical point of view is more close to the Modified Hartmann sensor. Here we introduce the theoretical
background and principles along with an example of phase derivative estimate based on a computer simulation. The
technique looks very promising since it is simple, with high resolution, without moving parts and allows us an easy post
processing to recover Zernike coefficients. Nevertheless, a lot of work has to be completed to a proper evaluation of its
actual capabilities, noise, resolution, etc.
New discoveries in astronomy require the use of ever larger telescopes. These telescopes require segmented apertures, since current technology does not provide for the fabrication of monolithic mirrors with diameters much larger than 8 m. As a result, the point spread function (PSF) of the system presents a diffraction pattern characteristic of the segmentation geometry, and this complicates the task of detecting faint structures with high spatial resolution. In this work, we investigate the use of amplitude filters at the pupil plane to decrease the intensity of this diffraction pattern. It is sufficient if this diffraction pattern is reduced below the residual halo that remains after adaptive optics compensation, so that the intensity distribution that surrounds the PSF core is limited by scattering rather than diffraction. We show different kinds of filters that allow us to achieve this goal. We analyze their performance, taking into account some unavoidable errors in the telescope operation such as imperfect phasing of the telescope segments and gaps between them. Finally, we discuss the application of the technique considering errors in the adaptive optics correction.
There are two main ways to address the wavefront sensing problem with modal wavefront sensors. First, the slope approximation that estimates a series of local first derivatives of the wavefront, as in the Hartmann-Shack sensor. Secondly, the curvature approximation, that estimates a series of second derivatives of the wavefront in different areas, as in the curvature sensor. It has been demonstrated that optical differentiation can be used as a useful first derivative wavefront sensor. Here we present a complete review of this new sensor along with a novel procedure to estimate the curvature of the wavefront phase using optical differentiation. This sensor consists of a telescopic system located in one of the arms of an interferometer and a phase step in the other arm. A variable amplitude transmission mask is placed at the focal plane of the telescopic system to perform the second derivative of the incoming field. A detailed description of the set-up and the mask is presented. The main advantages of this sensor are high resolution and easily adjusting of the sampling of the wavefront so allowing its use in high resolution wavefront sensing.
KEYWORDS: Point spread functions, Transmittance, Polarizers, Optical storage, Confocal microscopy, Diffraction, Super resolution, Photonics, Image processing, Control systems
The light intensity distribution near focus of an optical system can be modified by pupil-plane masks. In fact, in some relevant fields, such as optical data storage or confocal microscopy, there is an increasing interest in the design of pupil masks for controlling the Point Spread Function (PSF). These techniques present a great advantage for educational purposes, since they deal with current technology but at the same time illustrate basic diffraction principles. In this work, we introduce a simple low-cost set up that allows the dynamical control of the PSF and can be easily implemented in any educational centre.
An increasing number of both civilian and military applications require the motion description of translating targets from a sequence of frames acquired through long atmospheric paths. These images are randomly distorted, due to atmospheric turbulence, although adaptive optics systems can partially compensate for this distortion in real time. In these adverse conditions, a velocimetry technique that is based on the spatio-temporal Fourier transform of a series of images presents several advantageous features. In those cases where the target is very dim or an additional processing time reduction is needed, low-light-level images are recorded. Consequently, we have developed a simulation algorithm that generates atmospherically distorted low-light-level images corresponding to different atmospheric conditions and different degrees of compensation. In this paper, simulated low-light-level images are used to analyze the technique accuracy for estimating the object velocity for several atmospheric conditions and for different correction degrees.
The appearance of commercial spatial light modulators (SLM) opens new ways for teaching some optical phenomena. There are possible applications in a great variety of fields: interferometry, diffraction theory, simulation and compensation of random media, Fourier Optics, etc. In this paper, we propose the use of low cost liquid crystals displays (LCDs) as SLMs to perform some interesting optical experiments. The liquid crystal SLMs are extracted from a commercial video projector. This is one of the cheapest ways to obtain a SLM. For phase modulation, it requires the calibration of the system, because the manufacturers do not provide the physical specifications of the LCDs. This work is quite instructive since many different aspects are involved in the calibration process. Finally, we show an experiment using this setup, which demonstrates that the proposed SLM is an easy-to-use and flexible tool to show some well-known optical phenomena.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.