Tatyana Yu. Cherezova

Cw industrial rod YAG:Nd 3+ laser with an intracavity active bimorph mirror

A special type of resonator with an intracavity wide-aperture active mirror was built, and a concave spherical bimorph active corrector was investigated. An increase of laser beam quality by a factor of 2-2.5 was achieved in a multimode regime of laser generation with an intracavity-controlled mirror. It was shown that various radiation mode structures could be formed at the laser output and in the far-field zone.

Doughnut-like laser beam output formation by intracavity flexible controlled mirror

The formation of the given low loss and large beamwidth doughnut-like fundamental mode of stable resonator by an intracavity flexible mirror is discussed. The mirror is a bimorph one with one round and two ring controlling electrodes. An inverse propagation method is used to determine the appropriate shape of the controlled mirror. The mirror reproduces the shape with minimal RMS error by combining weights of experimentally measured response functions of the mirror sample. The voltages applied to each mirror electrode are calculated. The calculations are carried out for industrial CW CO2 laser.

Super-Gaussian laser intensity output formation by means of adaptive optics

An optical resonator using an intracavity adaptive mirror with three concentric rings of controlling electrodes, which produc low loss and large beamwidth super-Gaussian output of order 4, 6, 8, is analyzed. An inverse propagation method is used to determine the appropriate shape of the adaptive mirror. The mirror reproduces the shape with minimal RMS error by combining weights of experimentally measured response functions of the mirror sample. The voltages applied to each mirror electrode are calculated. Practical design parameters such as construction of an adaptive mirror, Fresnel numbers, and geometric factor are discussed.

Human eye anisoplanatism: eye as a lamellar structure

In this paper we consider anisoplanatism effect as a fundamental limitation on the size of high resolution area (isoplanatic patch) of retinal images obtained using fundus cameras equipped with adaptive optics. Isoplanatic patch size was estimated using experimental results for on-axis and off-axis eye aberrations measured by Shack-Hartmann technique. Isoplanatic patch size varied among examined subjects in the range from 1.5o to 2.5o which is in good agreement with results obtained using ray-tracing technique1. We estimated isoplanatic patch size for Gullstrand eye model and found it to be close to the values obtained from experimental results for subjects with good vision. We also discuss the possibilities of Gullstrand eye model modifications for modeling anisoplanatism effect for each particular subject. We also estimated the efficiency of multibeacon correction method and found out that this method allows us to almost twice increase the area with high resolution.

Custom-oriented wavefront sensor for human eye properties measurements

The problem of correct measurement of human eye aberrations is very important with the rising widespread of a surgical procedure for reducing refractive error in the eye, so called, LASIK (laser-assisted in situ keratomileusis). In this paper we show capabilities to measure aberrations by means of the aberrometer built in our lab together with Active Optics Ltd. We discuss the calibration of the aberrometer and show invalidity to use for the ophthalmic calibration purposes the analytical equation based on thin lens formula. We show that proper analytical equation suitable for calibration should have dependence on the square of the distance increment and we illustrate this both by experiment and by Zemax Ray tracing modeling. Also the error caused by inhomogeneous intensity distribution of the beam imaged onto the aberrometers Shack-Hartmann sensor is discussed.

LWIR and MWIR ultraspectral Fourier transform imager

Kestrel Corporation has designed and is now building a dual- band infrared Fourier transform ultraspectral imager for aircraft deployment. Designed for installation in a Cessna 206, this instrument will have a 15 degree FOV, with an IFOV of 1.0 mrad. The target spectral resolution is better than 1.5 cm-1 over 2000 to 3000 cm-1 and 0.4 cm-1 over 850 to 1250 cm(superscript -1

Human retina imaging: widening of high resolution area

. using 512 spectral channels. The device will use a variety of spectral enhancement techniques to achieve this unprecedented spectral resolution. Computer simulations of the optical systems demonstrates sub-wavenumber resolutions and signal to noise ratios of over 900.

Anisoplanatism in human retina imaging

In this paper we consider different methods of widening high resolution retinal image area. The first method is based on compensation of an average phase of two beacons formed on human retina within the isoplanatic patch. The second one is based on compensation of external corneal surface refraction with the help of immersion liquid. In both methods we use a single wavefront corrector conjugated to the pupil plane. The immersion method was found to be the most appropriate as it allows one to increase the area of high resolution almost twice without loss of image quality.

Ultraspectral imaging: A new contribution to global virtual presence

All extended optical systems with aberrations suffer from anisoplanatism effect. In this presentation we investigate anisoplanatism in human eye. For that purpose we use a reference source (beacon) obtained by focusing of a dim laser beam on the retina and consider increasing the retina resolution within anisoplanatic angle by means of ideal wavefront corrector and a real bimorph flexible one. The numerical simulations of isoplanatic patch size of human retina were made for different beacon positions and based on the aberrations measured by means of custom wavefront-guided aberrometer. We found out that in particular human eye the existence of optimal correction directions is possible. As the behavior of Zernike coefficients varies from subject to subject the existence of optimal correction angle is a feature of a particular eye. We also estimated the contribution of low-order and high-order aberrations in anisoplanatism effect for the subjects we measured. We found out that aberrations with strongly variable amplitude across the visual field have effect on the isoplanatic patch size most. In this paper we illustrated the isoplanatic patch enlargement with variation of beacon position by presenting two-dimensional retina and test object images. Also anisoplanatism in two-layer human eye model has been discussed. As the main part of the eyes aberrations is induced by the surfaces of the cornea and the crystal lens, our model consists of two thin phase screens that correspond to the cornea and the lens. Then we used such two-layer model to minimize residual mean-square error of correction by means of just one applied corrector.

Genetic algorithm for intracavity laser beam shaping

A new technology, Ultraspectral Imaging (USI) offers the capability to extend spectral imaging to a level where molecular adsorption or emission line features can be presented in a two-dimensional display. With these capabilities, unambiguous identification and mapping of gaseous constituents or solid material by their spectral features becomes possible. One of the techniques that shows the potential to collect these type of data is a proposed USI-based on a Fourier transform ultraspectral imager operating in the 3 pm to 5 pm and 8 pm to 12 pm bands designed for installation in an aircraft. This proposed instrument will have a 15 degree field of view (FOV), with an instantaneous field of view (IFOY) of 1.0 mrad. The target spectral resolution is better than 1.5 cm/sub -1/over 2000 to 3000 cm/sub -1/and 0.4 cm/sub -1/over 850 to 1250 cm/sub -1/using 512 spectral channels. The device will use a variety of spectral enhancement techniques to achieve this unprecedented spectral resolution. Computer simulations of the optical systems demonstrate subwavenumber resolutions and signal to noise ratios of over 900.