Showing papers on "Wavefront published in 2005"
TL;DR: This paper describes an alternative approach in which the full matrix of time domain signals from every transmitter–receiver pair is captured and post-processed and shown to offer significant performance advantages for NDE.
Abstract: Processing of ultrasonic array data is traditionally based on having parallel transmission circuits that enable staggered firing of transmitter elements to produce the desired wavefront. This paper describes an alternative approach in which the full matrix of time domain signals from every transmitter–receiver pair is captured and post-processed. Various post-processing approaches are modelled and assessed in terms of their ability to image a point-like reflector. Experimental results are then presented which show good quantitative agreement with the modelled results. An advanced processing algorithm is also implemented which allows the array to be focused at every point in the target region in both transmission and reception. This approach is shown to offer significant performance advantages for NDE.
747 citations
TL;DR: Computer-generated holography technique is a powerful technology suitable for a wide range of display types, including 2D, stereoscopic, autostereoscopic, volumetric, and true 3D imaging.
Abstract: Computer-generated holography technique is a powerful technology suitable for a wide range of display types, including 2D, stereoscopic, autostereoscopic, volumetric, and true 3D imaging. Computer-generated holography is an emerging technology, made possible by increasingly powerful computers, that avoids the interferometric recording step in conventional hologram formation. Instead, a computer calculates a holographic fringe pattern that it then uses to set the optical properties of a spatial light modulator, such as a liquid crystal microdisplay. The SLM then diffracts the readout light wave, in a manner similar to a standard hologram, to yield the desired optical wavefront. Although CGH-based display systems can be built today, their high cost makes them impractical for many applications.
342 citations
TL;DR: In this paper, the effects of photon noise, aliasing, wave front chromaticity, and scintillation on the point-spread function (PSF) contrast achievable with ground-based adaptive optics (AO) are evaluated for different wave front sensing schemes.
Abstract: The effects of photon noise, aliasing, wave front chromaticity, and scintillation on the point-spread function (PSF) contrast achievable with ground-based adaptive optics (AO) are evaluated for different wave front sensing schemes. I show that a wave front sensor (WFS) based on the Zernike phase contrast technique offers the best sensitivity to photon noise at all spatial frequencies, while the Shack-Hartmann WFS is significantly less sensitive. In AO systems performing wave front sensing in the visible and scientific imaging in the near-IR, the PSF contrast limit is set by the scintillation chromaticity induced by Fresnel propagation through the atmosphere. On an 8 m telescope, the PSF contrast is then limited to 10-4 to 10-5 in the central arcsecond. Wave front sensing and scientific imaging should therefore be done at the same wavelength, in which case, on bright sources, PSF contrasts between 10-6 and 10-7 can be achieved within 1'' on an 8 m telescope in optical/near-IR. The impact of atmospheric turbulence parameters (seeing, wind speed, turbulence profile) on the PSF contrast is quantified. I show that a focal plane wave front sensing scheme offers unique advantages, and I discuss how to implement it. Coronagraphic options are also briefly discussed.
294 citations
TL;DR: A method by which the phase and the amplitude of a wave front are obtained by processing a sequence of intensity patterns recorded at different planes, which does not use any reference wave.
Abstract: We present a method by which the phase and the amplitude of a wave front are obtained by processing a sequence of intensity patterns recorded at different planes. We do not use any reference wave, as one does for holography. Simulations and experimental results are presented.
263 citations
TL;DR: It is revealed that in fact there are no new aberrations in imaging optical systems with near-circular aperture stops but otherwise without symmetry, and that the field dependence of an aberration often changes when symmetry is abandoned.
Abstract: Many authors, dating back to at least the 1950s, have presented mathematical expansions of the wave-front aberration function for optical systems without symmetry, typically based on limiting assumptions and simplifications, with some of the most recent work being done by Howard and Stone [Appl. Opt.39, 3232 (2000) ]. This paper reveals that in fact there are no new aberrations in imaging optical systems with near-circular aperture stops but otherwise without symmetry. What does occur is that the field dependence of an aberration often changes when symmetry is abandoned. Each aberration type develops a characteristic field behavior in a system without symmetry. Specifically, for example, astigmatism, develops a binodal field dependence; e.g., there are typically two points in the field with zero astigmatism, and typically neither point is on axis. This construct, nodal aberration theory, for understanding the aberrations in systems without symmetry becomes a direct extension of an optical designer’s knowledge base. Through the use of real ray-based analysis methods, such as Zernike coefficients, it is possible to understand completely the aberrations of optical systems without symmetry in terms of rotationally symmetric aberration theory with the simple addition of the concept of field nodes.
249 citations
TL;DR: In this paper, a grid-based numerical scheme for tracking the evolution of monotonically advancing interfaces, via finite-difference solution of the eikonal equation, known as the fast marching method (FMM), is presented.
Abstract: The accurate prediction of seismic traveltimes is required in many areas of seismology, including the processing of seismic reflection profiles, earthquake location, and seismic tomography at a variety of scales. In this paper, we present two seismic applications of a recently developed grid-based numerical scheme for tracking the evolution of monotonically advancing interfaces, via finite-difference solution of the eikonal equation, known as the fast marching method (FMM). Like most other practical grid-based techniques, FMM is only capable of locating the first-arrival phase in continuous media; however, its combination of unconditional stability and rapid computation make it a truly practical scheme for velocity fields of arbitrary complexity. The first application of FMM that we present focuses on the prediction of multiple reflection and refraction phases in complex 2D layered media. By treating each layer that the wavefront enters as a separate computational domain, we show that sequential application of FMM can be used to track phases comprising any number of reflection and transmission branches in media of arbitrary complexity. We also show that the use of local grid refinement in the source neighbourhood, where wavefront curvature is high, significantly improves the accuracy of the scheme with little extra computational expense. The second application of FMM that we consider is in the context of 3D teleseismic tomography, which uses relative traveltime residuals from distant earthquakes to image wavespeed variations in the Earth’s crust and upper mantle beneath a seismic array. Using teleseismic data collected in Tasmania, we show that FMM can rapidly and robustly calculate two-point traveltimes from an impinging teleseismic wavefront to a receiver array located on the surface, despite the presence of significant lateral variations in wavespeed in the intervening crust and upper mantle. Combined with a rapid subspace inversion method, the new FMM based tomographic scheme is shown to be extremely efficient and robust.
230 citations
TL;DR: In this paper, an interferometric method was proposed to measure the shape of a hard-x-ray wavefront, which consists of a phase grating as a beam splitter and an absorption mask for the detector.
Abstract: We present an interferometric method to measure the shape of a hard-x-ray wavefront. The interferometer consists of a phase grating as a beam splitter and an absorption grating as a transmission mask for the detector. The device can be used to measure wavefront shape gradients corresponding to radii of curvature as large as several dozens of meters, with a lateral resolution of a few microns. This corresponds to detected wavefront distortions of approximately 10−12m or λ∕100. The device was used with 12.4 keV x rays to measure the slope error and height profile of an x-ray mirror. Surface slope variations with periods ranging from less than 1 mm to more than 1 m can be detected with an accuracy better than 0.1μrad.
172 citations
TL;DR: It is concluded that the one-to-one stimulus/response slope in accommodation function should not always be considered as ideal, because higher order aberrations, especially changes of spherical aberration, may influence the actual accommodative demand.
Abstract: It is well accepted that the accommodation system is characterized by steady-state errors in focus. The purpose of this study was to correlate these errors with changes in ocular wavefront aberration and corresponding image quality when accommodating. A wavefront analyzing system, the Complete Ophthalmic Analysis System (COAS), was used in conjunction with a Badal optometer to allow continuous recording of the aberration structure of the eye for a range of accommodative demands (up to 8 D). Fifty consecutive recordings from seven subjects were taken. Monocular accommodative response was calculated as (i) the equivalent refraction minimizing wavefront error and (ii) the defocus needed to optimize the modulation transfer function at high spatial frequencies. Previously reported changes in ocular aberrations with accommodation (e.g., the shift of spherical aberration to negative values) were confirmed. Increased accommodation errors for near targets (lags) were evident for all subjects, although their magnitude showed a significant intersubject variability. It is concluded that the one-to-one stimulus/response slope in accommodation function should not always be considered as ideal, because higher order aberrations, especially changes of spherical aberration, may influence the actual accommodative demand. Fluctuations may serve to preserve image quality when errors of accommodation are moderate, by temporarily searching for the best focus.
159 citations
Patent•
20 Jul 2005
TL;DR: In this article, the authors provided a liquid crystal lens element having a lens function capable of performing spherical aberration correction including a power component equivalent to a focal point change of the stable incident light in accordance with the voltage applied.
Abstract: There is provided a liquid crystal lens element having a lens function capable of performing spherical aberration correction including a power component equivalent to a focal point change of the stable incident light in accordance with the voltage applied. One (12) of the two transparent substrates (11, 12) has a transparent electrode (15) and a Fresnel lens surface (17) while the other (11) of the two transparent substrates has a phase correction surface (18) and a transparent electrode (16). Thus, by arranging the Fresnel lens surface (17) and the liquid crystal layer (13) between the two transparent electrodes (15, 16), the substantial refraction factor distribution of the liquid crystal layer (13) is changed according to the voltage applied, so that positive/negative power is given to the wavefront transmitting through the liquid crystal layer (13), the Fresnel lens surface (17), and the phase correction surface (18).
157 citations
TL;DR: This work describes the programmable spatial beam shaping of 100-kHz, 4-microJ amplified femtosecond pulses in a focal plane by wave-front modulation and obtains top-hat, doughnut, square, and triangle shapes of 20-microm size.
Abstract: We describe the programmable spatial beam shaping of 100-kHz, 4-?J amplified femtosecond pulses in a focal plane by wave-front modulation. Phase distributions are determined by a numerical iterative procedure. A nonpixelated optically addressed liquid-crystal light valve is used as a programmable wave-front tailoring device. Top-hat, doughnut, square, and triangle shapes of 20-?m size are obtained in a focal plane. Their suitability for femtosecond laser machining is demonstrated.
148 citations
TL;DR: A novel algorithm for modeling electrical wave propagation in anatomical models of the heart using a phase-field approach that represents the boundaries between the heart muscle and the surrounding medium as a spatially diffuse interface of finite thickness is presented.
Abstract: We present a novel algorithm for modeling electrical wave propagation in anatomical models of the heart. The algorithm uses a phase-field approach that represents the boundaries between the heart muscle and the surrounding medium as a spatially diffuse interface of finite thickness. The chief advantage of this method is to automatically handle the boundary conditions of the voltage in complex geometries without the need to track the location of these boundaries explicitly. The algorithm is shown to converge accurately in nontrivial test geometries with no-flux (zero normal current) boundary conditions as the width of the diffuse interface becomes small compared to the width of the cardiac action potential wavefront. Moreover, the method is illustrated for anatomically realistic models of isolated rabbit and canine ventricles as well as human atria.
TL;DR: The response to a short mechanical excitation on one side of the system is found to be a propagating coherent wave front followed by random oscillations made of multiply scattered waves, and it is found that the coherentWave front is insensitive to details of the packing.
Abstract: We present numerical simulations of acoustic wave propagation in confined granular systems consisting of particles interacting with the three-dimensional Hertz-Mindlin force law. The response to a short mechanical excitation on one side of the system is found to be a propagating coherent wave front followed by random oscillations made of multiply scattered waves. We find that the coherent wave front is insensitive to details of the packing: force chains do not play an important role in determining this wave front. The coherent wave propagates linearly in time, and its amplitude and width depend as a power law on distance, while its velocity is roughly compatible with the predictions of macroscopic elasticity. As there is at present no theory for the broadening and decay of the coherent wave, we numerically and analytically study pulse propagation in a one-dimensional chain of identical elastic balls. The results for the broadening and decay exponents of this system differ significantly from those of the random packings. In all our simulations, the speed of the coherent wave front scales with pressure as p1/6; we compare this result with experimental data on various granular systems where deviations from the p1/6 behavior are seen. We briefly discuss the eigenmodes of the system and effects of damping are investigated as well.
TL;DR: Wave-front sensors are able to resolve wave-front spatial frequencies 3 to 4 times higher than a conventional Shack-Hartmann technique using an equivalent CCD detector, and their dynamic is also much higher, 2 to 3 orders of magnitude.
Abstract: Multiple-wave achromatic interferometric techniques are used to measure, with high accuracy and high transverse resolution, wave fronts of polychromatic light sources. The wave fronts to be measured are replicated by a diffraction grating into several copies interfering together, leading to an interference pattern. A CCD detector located in the vicinity of the grating records this interference pattern. Some of these wave-front sensors are able to resolve wave-front spatial frequencies 3 to 4 times higher than a conventional Shack–Hartmann technique using an equivalent CCD detector. Its dynamic is also much higher, 2 to 3 orders of magnitude.
TL;DR: The neural sharpness metric can provide a single number that describes the subjective impact of each patient's wave aberration and will also increase the accuracy of refraction estimates from wavefront-based autorefractors and phoropters.
Abstract: Purpose. Despite the proliferation of wavefront sensors to characterize the optical quality of individual eyes, there is not yet an accurate way to determine from a wave aberration how severely it will impact the patient's vision. Some of the most commonly used metrics, such as RMS wavefront error and the Strehl ratio, predict subjective image quality poorly. Our goal is to establish a better metric to predict subjective image quality from the wave aberration. Methods. We describe three kinds of experiments designed to compare the effectiveness of different metrics in determining the subjective impact of the wave aberration. Subjects viewed a visual stimulus through a deformable mirror in an adaptive optics system that compensated for the subject's wave aberration. In the first experiment, we show that some Zernike modes such as spherical aberration and defocus interact strongly in determining subjective image quality. In the second experiment, the subject's wave aberration was replaced by the wave aberration corresponding to an individual Zernike mode. The subject then adjusted the coefficient of the Zernike mode to match the blur of a standard stimulus. In the third experiment, the subject viewed the same stimulus through the wave aberration of one of 59 different postoperative patients who had undergone LASIK and matched the blur by adjusting defocus. We then determined which among many image quality metrics best predicted these matching data. Results. RMS wavefront error was a poor predictor of the data, as was the Strehl ratio. Conclusions. The neural sharpness metric best described the subjective sharpness of images viewed through the wave aberrations of real eyes. This metric can provide a single number that describes the subjective impact of each patient's wave aberration and will also increase the accuracy of refraction estimates from wavefront-based autorefractors and phoropters. (Optom Vis Sci 2005;82:358-369)
TL;DR: The modal basis is the real Fourier basis, which allows direct control of specific regions of the point-spread function and is computationally efficient enough to be implemented with off-the-shelf technology for a 2.5 kHz, 64 x 64 adaptive optics system.
Abstract: Optimal modal Fourier-transform wavefront control combines the speed of Fourier-transform reconstruction (FTR) with real-time optimization of modal gains to form a fast, adaptive wavefront control scheme. Our modal basis is the real Fourier basis, which allows direct control of specific regions of the point-spread function. We formulate FTR as modal control and show how to measure custom filters. Because the Fourier basis is a tight frame, we can use it on a circular aperture for modal control even though it is not an orthonormal basis. The modal coefficients are available during reconstruction, greatly reducing computational overhead for gain optimization. Simulation results show significant improvements in performance in low-signal-to-noise-ratio situations compared with nonadaptive control. This scheme is computationally efficient enough to be implemented with off-the-shelf technology for a 2.5 kHz, 64×64 adaptive optics system.
TL;DR: The presented implementation provides a fast numerical method for studying the impact of aberration in medical ultrasound imaging through soft tissue - both on the transmitted beam and the nonlinearly generated harmonic beam.
Abstract: A method for simulating forward wavefront propagation in heterogeneous tissue is discussed. The intended application of this method is for the study of aberration produced when performing ultrasound imaging through a layer of soft tissue. A one-way wave equation that permits smooth variation in all acoustically important variables is derived. This equation also describes tissue exhibiting nonlinear elasticity and arbitrary frequency-dependent relaxation. A numerical solution to this equation is found by means of operator splitting and propagation along the spatial depth coordinate. The numerical solution is accurate when compared to analytical solutions for special cases, and when compared to numerical solutions of the full wave equation by other methods. The presented implementation provides a fast numerical method for studying the impact of aberration in medical ultrasound imaging through soft tissue - both on the transmitted beam and the nonlinearly generated harmonic beam.
Patent•
20 Apr 2005
TL;DR: A wavefront sensor is integrated with a surgical microscope for allowing a doctor to make repeated wavefront measurements of a patient's eye while the patient remains on an operating table in the surgical position as discussed by the authors.
Abstract: A wavefront sensor is integrated with a surgical microscope for allowing a doctor to make repeated wavefront measurements of a patient's eye while the patient remains on an operating table in the surgical position. The device includes a wavefront sensor optically aligned with a surgical microscope such that their fields of view at least partially overlap. The inclusion of lightweight, compact diffractive optical components in the wavefront sensor allows the integrated device to be supported on a balancing mechanism above a patient's head during a surgical procedure. As a result, the need to reposition the device and/or the patient between measuring optical properties of the eye and performing surgical procedures on the eye is eliminated. Many surgical procedures may be improved or enhanced using the integrated device, including but not limited to cataract surgery, Conductive Keratoplasty, Lasik surgery, and corneal corrective surgery.
TL;DR: Wavefront control experiments in strong scintillation conditions over a 2.33 km, near-horizontal, atmospheric propagation path are presented and mitigation of atmospheric distortions with a speckle beacon typical for directed energy and free-space laser communication applications is demonstrated.
Abstract: Wavefront control experiments in strong scintillation conditions (scintillation index, ≃1) over a 2.33 km, near-horizontal, atmospheric propagation path are presented. The adaptive-optics system used comprises a tracking and a fast-beam-steering mirror as well as a 132-actuator, microelectromechanical-system, piston-type deformable mirror with a VLSI controller that implements stochastic parallel gradient descent control optimization of a system performance metric. The experiments demonstrate mitigation of atmospheric distortions with a speckle beacon typical for directed energy and free-space laser communication applications.
TL;DR: WAinternal varied widely among patients, and a moderate to high degree of mirror symmetry existed between the right and left eyes, and internal surfaces compensated at least partially for the HOA and Symbol in most eyes, which decreased only mildly with increasing age.
Abstract: Purpose To analyze the distribution of human higher-order wavefront aberrations (3rd- to 6th-order) from the internal optics (WAinternal) and the variations with age and to evaluate the degree of compensation that the internal optics provide for anterior corneal aberrations (WAcornea). Setting Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Methods With assumption of a simple model for the eye, the WAinternal were obtained by direct subtraction of the WAcornea from the ocular aberrations (WAeye). The WAeye were measured using the WaveScan system (Visx, Inc.), and the WAcornea were computed from the topographic data (Humphrey Atlas) using the CTView program (Sarver and Associates, Inc.). In 144 eyes of 114 normal patients (age 20 to 69 years), WAinternal were calculated for a 6.0 mm pupil and a compensation factor (CF) was computed, with positive values representing compensation of WAcornea by WAinternal and negative values indicating that the internal surfaces add aberrations to those of the cornea. Results There was wide individual variation in WAinternal. The mean coefficient for 4th-order spherical aberration ( Z 4 0 ) was −0.145 μm ± 0.094 (SD) (95% confidence interval [CI], −0.160 to −0.130 μm); 95.1% of eyes had negative values. The mean root-mean-square value for HOAs was 0.334 ± 0.096 μm (95% CI, 0.319 to 0.350 μm). Moderate to high correlations were found between the right and left eyes in HOAs, 4th-order and 6th-order spherical aberration coefficients ( Z 4 0 and Z 6 0 ). With increasing age, the HOAs did not change, whereas the negative coefficients for Z 4 0 tended to become less negative. Only the term Z 4 0 had a CF significantly correlated with increasing age (r = −0.338, P Conclusion WAinternal varied widely among patients, and a moderate to high degree of mirror symmetry existed between the right and left eyes. Internal surfaces compensated at least partially for the HOA and Z 4 0 in most eyes, and this compensation decreased only mildly with increasing age.
TL;DR: In this article, the authors analyzed the fundamental limitations for the detection of extraterrestrial planets with Extremely Large Telescopes and showed that a coronagraphic device combined with a very high order wavefront correction system is required but not sufficient to achieve the $10^{-10}$ contrast level needed for detecting an Earth-like planet.
Abstract: We analyse the fundamental limitations for the detection of extraterrestrial planets with Extremely Large Telescopes. For this task, a coronagraphic device combined to a very high order wavefront correction system is required but not sufficient to achieve the $10^{-10}$ contrast level needed for detecting an Earth-like planet. The stellar residuals left uncorrected by the wavefront correction system need to be calibrated and subtracted. In this paper, we consider a general model including the dynamic phase aberrations downstream the wavefront correction system, the static phase aberrations of the instrument and some differential aberrations provided by the calibration unit. A rather optimistic case of a filled circular pupil and of a perfect coronagraph is elsewhere assumed. As a result of the analytical study, the limitation mostly comes from the static aberrations. Using numerical simulations we confirm this result and evaluate the requirements in terms of phase aberrations to detect Earth-like planets on Extremely Large Telescopes.
TL;DR: It is demonstrated that the pyramid can successfully simultaneously sense the piston, tip, and tilt of a segmented mirror, making this technique very attractive in phasing and aligning astronomical segmented telescopes such as extremely large telescopes currently under extensive studies.
Abstract: We report what is to our knowledge the first laboratory experiment that shows the use of a pyramid wavefront sensor to cophase and align segmented mirrors having three degrees of freedom per segment, i.e., piston, tip, and tilt. In the laboratory the iterative alignment procedure reached a wavefront residual error of about 10 nm. The residual error was equally distributed between piston, tip, and tilt. These results demonstrate that the pyramid can successfully simultaneously sense the piston, tip, and tilt of a segmented mirror. This last feature makes this technique very attractive in phasing and aligning astronomical segmented telescopes such as extremely large telescopes currently under extensive studies.
TL;DR: What is meant by wavefront aberration is outlined, and potential contact lens applications are outlined, including the design and on-eye performance of single-vision lenses, lenses for presbyopes and keratoconics, orthokeratology, tear film studies, and the design of customised contact lenses intended to minimise residual lens-eye wavefront error.
TL;DR: In this paper, the authors present a new realization of the textbook experiment consisting in single-photon interference based on the pulsed, optically excited photoluminescence of a single colour centre in a diamond nanocrystal.
Abstract: We present a new realization of the textbook experiment consisting in single-photon interference based on the pulsed, optically excited photoluminescence of a single colour centre in a diamond nanocrystal. Interferences are created by wavefront-splitting with a Fresnel’s biprism and observed by registering the “single-photon clicks” with an intensified CCD camera. This imaging detector provides also a real-time movie of the build-up of the single-photon fringes. We perform a second experiment with two detectors sensitive to photons that follow either one or the other interference path. Evidence for single photon behaviour is then obtained from the absence of time coincidence between detections in these two paths.
TL;DR: The goal here was to establish the quantitative relationship between optical upstroke morphology and subsurface wavefront orientation using computer modeling and test theoretical predictions experimentally in isolated coronary-perfused swine right ventricular preparations and discover characteristic saddle-shaped VF* maps that were in excellent agreement with theoretically predicted changes in wavefront expansion.
Abstract: The analysis of surface-activation patterns and measurements of conduction velocity in ventricular myocardium is complicated by the fact that the electrical wavefront has a complex 3D shape and can approach the heart surface at various angles. Recent theoretical studies suggest that the optical upstroke is sensitive to the subsurface orientation of the wavefront. Our goal here was to (1) establish the quantitative relationship between optical upstroke morphology and subsurface wavefront orientation using computer modeling and (2) test theoretical predictions experimentally in isolated coronary-perfused swine right ventricular preparations. We show in numerical simulations that by suitable placement of linear epicardial stimulating electrodes, the angle φ of wavefronts with respect to the heart surface can be controlled. Using this method, we developed theoretical predictions of the optical upstroke shape dependence on φ. We determined that the level V F * at which the rate of rise of the optical upstroke reaches the maximum linearly depends on φ. A similar relationship was found in simulations with epicardial point stimulation. The optical mapping data were in good agreement with theory. Plane waves propagating parallel to myocardial fibers produced upstrokes with V F * 0. Similarly, we obtained good agreement with theory for plane waves propagating in a direction perpendicular to fibers ( V F *>0.5 when φ V F * maps that were in excellent agreement with theoretically predicted changes in φ during wavefront expansion. Our findings should allow for improved interpretation of the results of optical mapping of intact heart preparations.
TL;DR: A new method to perform simultaneously three dimensional optical sectioning and optical manipulation is presented, which combines a multi trap optical tweezers with a video microscope to enable axial scanning of living cells while maintaining the trapping configuration at a fixed position.
Abstract: A new method to perform simultaneously three dimensional optical sectioning and optical manipulation is presented. The system combines a multi trap optical tweezers with a video microscope to enable axial scanning of living cells while maintaining the trapping configuration at a fixed position. This is achieved compensating the axial movement of the objective by shaping the wave front of the trapping beam with properly diffractive optical elements displayed on a computer controlled spatial light modulator. Our method has been validated in three different experimental configurations. In the first, we decouple the position of a trapping plane from the axial movements of the objective and perform optical sectioning of a circle of beads kept on a fixed plane. In a second experiment, we extend the method to living cell microscopy by showing that mechanical constraints can be applied on the dorsal surface of a cell whilst performing its fluorescence optical sectioning. In the third experiment, we trapped beads in a three dimensional geometry and perform, always through the same objective, an axial scan of the volume delimited by the beads.
TL;DR: A TIL propagation model that uses a combination of the parabolic equation describing coherent outgoing-wave propagation, and the equation describing evolution of the mutual correlation function (MCF) for the backscattered wave (return wave) is introduced.
Abstract: Target-in-the-loop (TIL) wave propagation geometry represents perhaps the most challenging case for adaptive optics applications that are related to maximization of irradiance power density on extended remotely located surfaces in the presence of dynamically changing refractive-index inhomogeneities in the propagation medium. We introduce a TIL propagation model that uses a combination of the parabolic equation describing coherent outgoing-wave propagation, and the equation describing evolution of the mutual correlation function (MCF) for the backscattered wave (return wave). The resulting evolution equation for the MCF is further simplified by use of the smooth-refractive-index approximation. This approximation permits derivation of the transport equation for the return-wave brightness function, analyzed here by the method of characteristics (brightness function trajectories). The equations for the brightness function trajectories (ray equations) can be efficiently integrated numerically. We also consider wave-front sensors that perform sensing of speckle-averaged characteristics of the wave-front phase (TIL sensors). Analysis of the wave-front phase reconstructed from Shack-Hartmann TIL sensor measurements shows that an extended target introduces a phase modulation (target-induced phase) that cannot be easily separated from the atmospheric-turbulence-related phase aberrations. We also show that wave-front sensing results depend on the extended target shape, surface roughness, and outgoing-beam intensity distribution on the target surface. For targets with smooth surfaces and nonflat shapes, the target-induced phase can contain aberrations. The presence of target-induced aberrations in the conjugated phase may result in a deterioration of adaptive system performance.
TL;DR: It is shown that for defocused traditional and wavefront-coded systems the OTF can be represented as a generalized Cornu spiral, which provides a physical insight into the way in which wavefront coding can increase the depth of field of an imaging system.
Abstract: We describe the mapping of the optical transfer function (OTF) of an incoherent imaging system into a geometrical representation. We show that for defocused traditional and wavefront-coded systems the OTF can be represented as a generalized Cornu spiral. This representation provides a physical insight into the way in which wavefront coding can increase the depth of field of an imaging system and permits analytical quantification of salient OTF parameters, such as the depth of focus, the location of nulls, and amplitude and phase modulation of the wavefront-coding OTF.
TL;DR: In this paper, a method to measure the aberrations of a high numerical aperture off-axis paraboloid and correct for these using adaptive optics has been described, which can be used to accurately calculate the electromagnetic field at the focus using the Stratton-Chu vector diffraction theory.
Abstract: We describe a method to measure the aberrations of a high numerical aperture off-axis paraboloid and correct for the aberrations using adaptive optics. It is then shown that the characterized aberrations can be used to accurately calculate the electromagnetic field at the focus using the Stratton–Chu vector diffraction theory. Using this methodology, an intensity of 7×1021 W/cm2 was demonstrated by focusing a 45-TW laser beam with an f/0.6, 90∘ off-axis paraboloid after correcting the aberrations of the paraboloid and the low-energy reference beam. The intensity can be further increased to 1×1022 W/cm2 by including in the correction algorithm the wavefront difference between the reference beam and the high-energy beam.
TL;DR: An optical circuit design method for coherent waves as a boundary value problem is proposed in which the refractive index pattern is automatically synthesized for given input and output fields with a numerical calculation.
Abstract: We propose an optical circuit design method for coherent waves as a boundary value problem. The method produces a very compact circuit in which the refractive index pattern is automatically synthesized for given input and output fields with a numerical calculation. We employ the method to design a 1.3?1.55??m wavelength demultiplexer and also describe the features of a circuit generated by use of the method.
Patent•
14 Feb 2005
TL;DR: In this paper, a free-space adaptive optical laser communication system has been proposed, where wavefront sensing and wavefront correction mechanisms are employed along signal transmission and reception channels of all terminals in the communication system (i.e. adaptive optics) to improve the condition of the laser beam at the receiver.
Abstract: A free-space adaptive optical laser communication system having signal transmission and reception channels at all terminals in the communication system, wherein wavefront sensing and wavefront correction mechanisms are employed along signal transmission and reception channels of all terminals in the communication system (i.e. adaptive optics) to improve the condition of the laser beam at the receiver (i.e. reduce the size of the spot the detector plane). Speckle-to-receiver-aperture tracking mechanisms are employed in the transmission channel of the communication system and laser beam speckle tracking mechanism in the reception channels thereof, so as to achieve a first level of optical signal intensity stabilization at signal detector of each receiving channel. Speckle-to-fiber/detector locking mechanisms are also employed in signal receiving channels of all terminals in the communication system so as to achieve a second level of optical signal intensity stabilization at signal detector of each receiving channel.