Influence Of Defocus Research Articles

Spatio-chromatic vision with multifocal diffractive intraocular lens

BackgroundThis study aims to detect alterations in the spatio-chromatic pseudophakic vision produced by multifocal diffractive intraocular lenses (IOLs) and provides a physical interpretation.MethodsIn vitro characterization of the imaging performance of two diffractive IOLs: AT LISA Tri (Zeiss) and FineVision (PhysIOL) in on-bench model eye illuminated with red (R, 625 nm), green (G, 530 nm) and blue (B, 455 nm) lights. We used the metrics: energy efficiency (EE), area under the modulation transfer function, longitudinal chromatic aberration (LCA), and halo intensity. Through-focus (TF) analysis and calculation of the expected defocus curve under white (W) daylight were included. In vivo visual acuity (VA) of 50 pseudophakics (60 eyes) was assessed under W, R, G, B lights at far and near. Two clinical experiments evaluated LCA and R, G, B TF-EE effects on pseudophakic vision and their relative importance.ResultsClinical mean VA values under W light agreed with the predicted values at far and near for both IOLs. LCA measurements and R, G, B TF-EE curves were consistent with their lens design based on the 0th and 1st diffraction orders operative for far and near vision, respectively. LCA effects were compensated at near but noticed at far (− 0.75 D under B light). We detected strong asymmetry in visual resolution depending on the object distance and the illuminating wavelength—red predominance at far, blue predominance at near—in consistency with the TF-EE measurements.ConclusionsDiffractive multifocal IOL designs produce asymmetries in the spatio-chromatic vision of pseudophakics beyond the alterations strictly due to LCA. VA asymmetry for far/near object distance under R and B illumination is clinically detectable in subjects implanted with IOLs with 0th and 1st diffraction orders for far and near vision, respectively. Such VA asymmetry cannot be explained solely from the influence of defocus, as would be derived from a chromatic difference of power, but mainly from the wavelength dependence of the EE.

A novel phase unwrapping method for binocular structured light 3D reconstruction based on deep learning

Fringe projection has been prevalently adopted in the field of three-dimensional(3D) reconstruction. However, it is still a challenge to achieve high-precision and efficient measurement. To achieve real-time and efficient 3D shape measurement of the objects, we must extract the 3D coordinate data of the object from as few fringe patterns as possible. In the paper, we develop a new technique combining composite fringe coding and stair phase coding to solve the high-quality absolute phase and realize binocular 3D morphology reconstruction based on deep learning. This method only needs to project a composite fringe coding pattern to acquire the wrapped phase and a stair phase coding pattern to obtain the fringe order. Then we can recover the unwrapped phase maps of the captured fringe patterns. According to the calibration parameters of the binocular camera, the absolute phase is stereo matched to get the disparity map, and then converted into 3D spatial coordinates of the object. The influence of defocus and noise on the deviation between the wrapped phase and fringe order is solved by staggered phase unwrapping method. We demonstrated the validity and robustness of the novel method by experiments, which provides a promising research direction for 3D shape measurement based on binocular structured light.

Engineering of Aberrated PSF by Asymmetric Apodization with the Complex Shaded Aperture

The point spread function (PSF) produced by a coherent optical system under the influence of defocus, coma, and primary spherical aberration (PSA) is examined in this work. This paper deals with asymmetric apodization and pupil engineering to control monochromatic aberrations. To reduce the influence of monochromatic aberrations on the diffracted PSF, this approach uses amplitude and phase apodization. Analytical investigations on intensity PSF are carried out with varying amounts of aberrations and degrees of amplitude and phase apodization. Computed central peak intensity and full width at half maxima (FWHM) and analyzed. The resolution of a diffraction-limited optical imaging system is improved by using an asymmetric optical filter that minimizes the effect of defocus.

离焦对激光通信接收视场的影响分析

离焦对激光通信接收视场的影响分析

离焦对激光通信接收视场的影响分析

离焦对激光通信接收视场的影响分析

Influence of defocus on quantitative analysis of microscopic objects and individual cells with digital holography.

Digital holography offers a unique method for studying microscopic objects using quantitative measurements of the optical phase delays of transmitted light. The optical phase may be integrated across the object to produce an optical volume measurement, a parameter related to dry mass by a simple scaling factor. While digital holography is useful for comparing the properties of microscopic objects, especially cells, we show here that quantitative comparisons of optical phase can be influenced by the focal plane of the measurement. Although holographic images can be refocused digitally using Fresnel propagation, ambiguity can result if this aspect is not carefully controlled. We demonstrate that microscopic objects can be accurately profiled by employing a digital refocusing method to analyze phase profiles of polystyrene microspheres and red blood cells.

Combined analysis of tunable phase mask within spatial and frequency domain

Wavefront coding technique is a powerful technique which overcomes the defects of traditional way to extend depth of field. By inserting a phase mask into the traditional incoherent imaging system, wavefront coding technique does not reduce the resolution and the light gathering power of the optical system but enlarges the depth of field of incoherent imaging system. Although several kinds of phase masks have been reported, cubic phase mask is still of a classical type which has been investigated widely both in spatial and frequency domain. Since the phase profiles of phase masks adopted in classical wavefront coding systems are predefined with specific optical systems, the extension of depth of field is not tunable. Tunable wavefront coding systems are introduced by using a pair of detachable phase masks, which is possible to control the depth of field and bandwidth of system by changing the position of each component with respect to the pupil center. Ojeda-Castaeda [Ojeda-Castaeda J, Rodrguez M, Naranjo R 2010 Proceedings of Progress in Electronics Research Symposium, Cambridge, July 58, 2010 p531] proposed to use a pair of cosine phase masks to make defocus sensitivity tunable. Zhao [Zhao H, Wei J X 2014 Opt. Commun. 326 35] investigated an improved version of Ojeda- Castaneda's design in frequency domain and found that the proposed system realized tunable bandwidth. The present study, based on the work of Zhao, analyzes the tunable characteristics of a pair of simple modified detachable cubic phase masks in spatial domain and frequency domain. Firstly, the ray aberration theory is adopted to give mathematical analyses and ray aberration maps of the proposed tunable phase mask. Based on the mathematical derivations, the size of point spread function (PSF) of system can be changed not only by profile of each cubic mask but also by the each mask displacement relative to pupil center. Secondly, a mathematical PSF based on the stationary phase method is derived in spatial domain. Simulations indicate that the positions of PSF translate in the image plane with the displacements of phase mask profile and the position of each component with respect to the pupil center. By analyzing the oscillations of PSF, the effective bandwidth is obtained. Through the expression, we can conclude that the effective bandwidth can be changed by the position, mask profile of each component and defocus. Only when the addition of two mask profiles is large enough, can the effective bandwidth be simplified without adding the influence of defocus. In addition, though the approximate expression of magnitude transfer of function (MTF) has been given by adopting stationary phase method in the appendix of previous work, it cannot give an intuitive grasp of the effective bandwidth in MTF map. Unlike the MTF expression derived before, the exact optical transfer function (OTF) expression is derived by adopting Fresnel integral in frequency domain. Exact MTF and phase transfer function (PTF) can be derived from OTF. Based on the exact MTF expression, simulations give an intuitive effective bandwidth in MTF map. Simulations also show the nonlinear property of PTF. The effective bandwidth and MTF can be changed by different phase mask profiles and positions, which indicate that the effective bandwidth and defocus sensitivity can be tuned. Analyses are conducted both in spatial domain and in frequency domain to verify the tunable property of the proposed phase mask, which provides theoretical foundation for tunable wavefront coding system design.

Optical parameters and space–bandwidth product optimization in digital holographic microscopy

This paper considers some of the most important optical parameters that characterize a digital holographic microscope (DHM) and presents their mathematical derivation based on geometrical and diffraction-based models. It supports and justifies the use of the out-of-focus recording of holograms by showing that the field of view can be increased when recording the hologram in front of the in-focus image plane. In this manner a better match between the space-bandwidth product (SBP) of the microscope objective and that of the reconstructed hologram can be obtained. Hence, DHM offers a more cost-efficient way to increase the recorded SBP compared to the application of a high-quality microscope objective (large numerical aperture and low magnification) used in conventional microscopy. Furthermore, an expression for the imaging distance (distance between hologram and image plane), while maintaining the optical resolution and sufficient sampling, is obtained. This expression takes into account all kinds of reference-wave curvature and can easily be transferred to lensless digital holography. In this context it could be demonstrated that an object wave matched reference wave offers a significantly smaller imaging distance and hence the largest recoverable SBP. In addition, a new, to our knowledge, approach, based on the influence of defocus on the modulation transfer function, is used to derive the depth of field (DOF) for a circular aperture (lens-based system) and a rectangular aperture (lensless system), respectively. This investigation leads to the finding that a rectangular aperture offers an increased resolution combined with an increased DOF, when compared to a circular aperture of the same size.

Accuracy Analysis of Centroid Detection Method Used to Star Sensor

Star sensor is important equipment for measuring satellite attitude and motion, and star centroid detection accuracy is the basis of the overall accuracy of star sensor. In star sensors, slightly- defocus method is often adopted to acquire dispersive light spots so as to facilitate centroid detection, and certain motion blur can also be introduced because of the motion of satellites. In this paper, we analyzed several commonly-used centroid detection algorithms by using simulation experiment to study the influence of defocus and motion parameters on the accuracy of centroid detection algorithm and provided acceptable parameter value ranges.

Superresolution lithography from the viewpoint of partially coherent imaging theory Part I: Line and space structures

The influence of the new methods of superresolution lithography on resolution limit and DOF is discussed for line and space structures. It could be shown that SHRINC, CQUEST, optical filtering and Levensons method cannot increase the optical resolution limit, but that they differ in transferable contrast and the influence of defocus.

Measurement of disability glare:the influence of defocus and media opacification

Disability glare, which is the loss of visual performance due to scattered or reflected light, was measured using both letter acuity and contrast sensitivity tasks. Visual performance measurements in the presence and absence of glare were obtained under conditions of simulated media opacification and induced defocus. Media opacification and defocus both affected contrast sensitivity and, for each condition, the reduction in visual performance was more marked at higher spatial frequencies. The addition of glare further reduced visual performance and this was measured more effectively by measurements of contrast sensitivity than by measurements of letter acuity.

Observation of surface treatments on single crystals by reflection electron microscopy

Atomic steps on single-crystal spheres of Au have been directly imaged in a conventional electron microscope in reflection mode. The microscope is equipped with a low-temperature goniometer stage, allowing conditions similar to ultrahigh vacuum for the specimen area. The different steps of UHV treatments for cleaning a surface, such as Ar-ion bombardment and annealing, have been studied. Furthermore, the influence of chemical etching and electro-polishing on the surface has been investigated. Subsequent annealing in UHV led again to atomically flat surface areas with monatomic steps. The UHV treatments were carried out in a separate UHV system. It was found that the same surface topography is observed after heating the crystal sphere in air. The intensity of surface imaging with a Bragg reflection at arbitrary azimuth is compared with imaging under the surface-resonance condition. In the latter case, a gain of intensity by a factor of about 4 for gold with increased contrast for the steps is obtained. The influence of defocus on surface details is discussed in connection with the imaging of surface reconstruction.