Amorphous chalcogenide thin films are excellent materials for holographic recordings. AsSeS thin film coating is a
useful optical material for it's thickness to be easily corrected with the use of exposure to light and consecutive chemical
etching. Following properties allow to treat the surface of AsSeS chalcogenide films and to use them in adaptive optics
systems for correction of the optical wavefront. Hereby, we characterize AsSeS film properties to be used for correction
of optical aberrations of the human eye. The thickness of the film is characterized with the method of spectrodensitometry and the surface profile depth with a Hartman- Shack waveform analyzator.
The purpose of this work is studying a corneal asphericity change after a myopic refractive correction by mean of
excimer lasers. As the ablation profile shape plays a key role in the post-op corneal asphericity, ablation profiles of
recent lasers should be studied. The other task of this research was to analyze operation (LASIK) outcomes of one of the
lasers with generic spherical ablation profile and to compare an asphericity change with theoretical predictions. The
several correction methods, like custom generated aspherical profiles, may be utilized for mitigation of unwanted effects
of asphericity change. Here we also present preliminary results of such correction for one of the excimer lasers.
Proc. SPIE. 6284, International Conference on Lasers, Applications, and Technologies 2005: Laser Technologies for Environmental Monitoring and Ecological Applications, and Laser Technologies for Medicine
We present the experimental implementation of ophthalmic diagnostic systems with adaptive optics compensation of
human eye aberration. The systems feature high speed operation and utilize deformable bimorph mirrors for wavefront
correction. The results of aberration measurements and correction are discussed.
The spatial resolution of retinal images is limited by the presence of static and time-varying aberrations present within the eye. An updated High Resolution Adaptive Optics Fundus Imager (HRAOFI) has been built based on the development from the first prototype unit. This entirely new unit was designed and fabricated to increase opto-mechanical integration and ease-of-use through a new user interface. Improved camera systems for the Shack-Hartmann sensor and for the scene image were implemented to enhance the image quality and the frequency of the Adaptive Optics (AO) control loop. An optimized illumination system that uses specific wavelength bands was applied to increase the specificity of the images. Sample images of clinical trials of retinas, taken with and without the system, are shown. Data on the performance of this system will be presented, demonstrating the ability to calculate near diffraction-limited images.
A new significantly redesigned version of clinically applicable adaptive optics multispectral fundus imager is presented. Along with greatly improve adaptive system loop rate, the device performs reliably and is convenient for use in clinical practice. This new imager has allowed us to use new approaches for retina image analysis and obtain original results on the distribution of aberrations in the human eye.
The spatial resolution of the retinal images cannot approach a diffraction limit due to the high-order aberrations of the human eye. We present a technique, which allows restoring fine details on the retinal images using information about OTF (optical transfer function) of the eye obtained by the Shack-Hartman wavefront sensor. The precision of wavefront measurements greatly enhanced by reference source scanning on the retina. A closed loop adaptive system based on the bimorph mirror suppresses low-order aberrations. The residual errors are removed by the image deconvolution. The finite depth of retina layers of the human eye significantly reduce resolution of color retinal images as far as it introduces additional defocusing depending on the wave- length of the reflecting light. We present a novel technique of color retinal image deconvolution. The key feature of the algorithm is in use of information on retina structure. This permits calculating of optical transfer functions for each of the retina layers. Significant improvement of image quality was obtained. The processing time was about a few dozens of seconds for contemporary PC computers and image size 2000*2000 pixels.
The capability of resolving fine details on retinal images plays a key role in early diagnostic of vision loss. Biochemical and morphological features, which may be present in the early stages of many retinal diseases, cannot be detected today with current funduscopic instruments because of the losses in spatial resolution introduced by the ocular medium and cornea. One of the ways of the solution of such a problem is to use the adaptive optical systems first for measuring phase distortions and then for its suppression. In our work we suggest the innovative approach that includes two stages of adaptive correction. On the first stage a Shack-Hartman wavefront sensor and modal flexible mirror is used for low-order aberration correction. On the second stage a computer post-processing, or deconvolution, of the residual aberrations is done using the information on the aberrations measured by the sensor. In our report we present the specific design of the Shack-Hartman wavefront sensor suitable for measurements of human eye aberrations. The characteristics of a modal bimorph corrector are discussed. The features of deconvolution technique are outlined.
We consider theoretically spatial pattern formation processes in a unidirectional ring cavity with thin layer of Kerr-type nonlinear medium. Our method is based on studying of two coupled equations. The first is a partial differential equation for temporal dynamics of phase modulation of light wave in the medium. It describes nonlinear interaction in the Kerr-type lice. The second is a free propagation equation for the intracavity field complex amplitude. It involves diffraction effects of light wave in the cavity.
Influence of the input field spatial stationary modulation (roll) on the pattern formation in a nonlinear optical system has been under theoretical and numerical investigation. We show that variation of the input field modulation amplitude dramatically change the spatial dynamics of the system. If the modulation amplitude is large enough stimulated patterns appear in the system output.
Pattern formation processes in passive nonlinear ring resonator were studied theoretically and numerically. The formation of not only 'classical' spatial patterns, such as roll, hexagon, and dodecagon, but more complicated flower- like patterns were analyzed. We found and described new dynamic regime in the cavity-spatial localized structure formation.
Dynamics of nonlinear interferometer with optical feedback was analytically and numerically studied. Mathematical model of the system was elaborated. Linear stability analysis in the sense of noise in the input field was carried out. Numerical simulation results were presented.
Transverse interactions and pattern formation processes occurring in passive ring resonator with thin Kerr medium are theoretically and numerically investigated. In the system diffraction effects can determine spatial destabilization of laser beam profile with formation of regular structures in a transverse plane. Theoretical model for the evolution of the intracavity field and nonlinear phase modulation in the medium was elaborated. System of equations for steady state phase and intensity was derived, and linear stability analysis was carried out. We make some simple predictions about spatial stability of a plane wave and prove the existence of instability domains linked to the onset of transverse modulation of the filed profile. Results of numerical simulations are also presented.
Transverse interactions in a passive ring resonator with Kerr slice are theoretically and numerically investigated. Using the method of nonlinear phase modulation expansion we obtained the system of equations for nonlinear modes. Stability analysis of resonator modes was carried out. We also studied intermode interactions and regular pattern formation processes in both cases of plane wave and circular aperture.
New types of nonlinear optical systems that use the joint effects of Kerr-like nonlinearity, interference and diffraction in 2-D optical feedback are analyzed. We show that spatio- temporal instabilities in these systems can exist in the form of conditional instability. By varying several parameters of the optical system it is possible to control the nonlinear dynamics, thus creating different regimes of intermode interactions.
We discuss a technique based on nonlinear and adaptive optics for simulation of phase distortion effects in imaging systems. This technique uses a nonlinear two-dimensional optical feedback system to produce a controllable spatially and temporally varying chaotic intensity distribution. The intensity pattern is converted into a spatially varying thin phase screen using a spatial phase modulator. A chaotic phase distortion is then introduced into an imaging system's output image by propagation through the phase screen. A deformable (adaptive) mirror with computer control is used for simulation of large-scale phase distortions.
The simplest spatially distributed neuromorphic dynamic system with large-scale spatio- temporal interaction is investigated. The model of the system is nonlinear optical ring cavity with field rotation around optical axis and signal time-delay in the two-dimensional feedback loop. The characteristics of rotary modes of the system are determined by the parameters of nonlocal spatio-temporal interconnections. The competition of rotary modes takes place like in neural networks of WTA type.