Amplitude Point Spread Function Research Articles

Metric-Based Visual Acuity and Defocus Curve Simulation of Two Multifocal Intraocular Lens Models.

PurposeTo predict clinical defocus curve performance of the PanOptix intraocular lens (IOL) model TFNT00, a population-based image quality metric was applied to a pseudophakic eye model.MethodsVisual acuity (VA) was simulated using a 2-surface reduced eye model. For each virtual eye, the derived corneal surface was combined with scaled IOL surface. Corneal power and aberration, anterior chamber depth, and pupil size were iterated using a Monte-Carlo approach. Image quality of the IOLs was assessed using the total aberration map to compute the amplitude point spread function. A diffraction-normalized light-in-the-bucket metric was calculated for each virtual eye for defocuses from −3.5 D to +1.0 D (step size 0.25 D) and transformed to VAs and defocus curves. Simulated VA for the ReSTOR +3.0 D lens was used to generate a calibration function by linear regression correlation of simulated data with clinical VA data. Simulated TFNT00 VA was then validated by comparing defocus curves to clinical TFNT00 data.ResultsFrom −3.5 D to +1.0 D, the simulated defocus curve was generally consistent with the defocus curve from the TFNT00 clinical trial. The mean absolute difference was 0.022 logMAR (~1 letter) for simulated VA versus clinical trial VA.ConclusionIOL image quality can be assessed using a population-based virtual eye model to simulate VA and predict clinical performance. Computational modeling and simulation can be applied to future IOL development before clinical trials are conducted.

Digital coronagraph algorithm

The detection of faint stellar companions requires high contrast techniques such as coronagraphy. To achieve such high contrast coronagraphs must work with the aid of adaptive optics or be mounted on space telescopes. We propose a new coronagraphic technique that consists of the digital processing of non-coronagraphic images. The only requirement is a priori knowledge of the telescope amplitude point spread function. This digital coronagraph algorithm presents the advantage that it avoids problems associated with manufacture, implementation, and alignment of optical coronagraphs. The digital coronagraph algorithm is successfully checked with laboratory generated images. Moreover, numerical simulations show that the digital coronagraph presents contrast curves similar to that of the optical coronagraph. Finally, speckle noise can be cancelled out as effectively as in optical coronagraphs.

Hybrid pupil filter design using Bessel series

We propose a simple method of designing pupil filters for transverse super-resolution. For this end we represent the amplitude Point Spread Function (PSF) as a series expansion, constructed from the Fourier transform of a basis of Bessel functions. With this representation we optimize the intensity PSF according to certain desired characteristics, such as a smaller disk diameter than the corresponding, clear aperture, Airy disk. It is proved that by using few basis functions, it is possible to design pupils with similar or better PSF characteristics than previously reported.

Simulation and experiment on generation of an arbitrary array of intense spots by a tiledhologram

We present a method that allows accurate simulation of the output intensity of an arbitraryarray of intense spots generated by a tiled hologram. In this method zero padding ofn times the number of data points in the matrix of the incident laser beam is appliedbefore Fourier transform to fully reveal the speckles and the reconstruction error.The resulting matrix is reduced to a smaller one by resampling at an interval ofn. The convolution of a matrix representing the amplitude point spread function of theoptical system and the reduced matrix gives the final output amplitude distribution. Awedge target is used as a test image. The experimental results are in excellent agreementwith the simulation.

Laser confocal microscope with wavelet-profiled point spread function

We report a laser-scanning confocal reflectance microscope with a wavelet-profiled point spread function (PSF) for rapid multi-resolution extraction and analysis of microscopic object features. The PSF is generated via holography by encoding a π-phase shifting disk unto a collimated laser beam via a phase-only spatial light modulator (SLM) that is positioned at the pupil plane of the focusing objective lens. Scaling of the transverse PSF distribution is achieved by selecting a suitable ratio of the π-phase shifting disk radius and the pupil aperture radius. With one and the same objective lens and one SLM to control the phase profile of the pupil function, we produce amplitude PSF distributions that are accurate scaled representations of the circularly-symmetric Mexican hat mother wavelet.

Amplitude point-spread function measurement of high-NA microscope objectives by digital holographic microscopy

We present here a three-dimensional evaluation of the amplitude point-spread function (APSF) of a microscope objective (MO), based on a single holographic acquisition of its pupil wavefront. The aberration function is extracted from this pupil measurements and then inserted in a scalar model of diffraction, allowing one to calculate the distribution of the complex wavefront propagated around the focal point. The accuracy of the results is compared with a direct measurement of the APSF with a second holographic system located in the image plane of the MO. Measurements on a 100 x 1.3 NA MO are presented.

On the complex three‐dimensional amplitude point spread function of lenses and microscope objectives: theoretical aspects, simulations and measurements by digital holography

The point spread function is widely used to characterize the three-dimensional imaging capabilities of an optical system. Usually, attention is paid only to the intensity point spread function, whereas the phase point spread function is most often neglected because the phase information is not retrieved in noninterferometric imaging systems. However, phase point spread functions are needed to evaluate phase-sensitive imaging systems and we believe that phase data can play an essential role in the full aberrations' characterization. In this paper, standard diffraction models have been used for the computation of the complex amplitude point spread function. In particular, the Debye vectorial model has been used to compute the amplitude point spread function of x63/0.85 and x100/1.3 microscope objectives, exemplifying the phase point spread function specific for each polarization component of the electromagnetic field. The effect of aberrations on the phase point spread function is then analyzed for a microscope objective used under nondesigned conditions, by developing the Gibson model (Gibson & Lanni, 1991), modified to compute the three-dimensional amplitude point spread function in amplitude and phase. The results have revealed a novel anomalous phase behaviour in the presence of spherical aberration, providing access to the quantification of the aberrations. This work mainly proposes a method to measure the complex three-dimensional amplitude point spread function of an optical imaging system. The approach consists in measuring and interpreting the amplitude point spread function by evaluating in amplitude and phase the image of a single emitting point, a 60-nm-diameter tip of a Near Field Scanning Optical Microscopy fibre, with an original digital holographic experimental setup. A single hologram gives access to the transverse amplitude point spread function. The three-dimensional amplitude point spread function is obtained by performing an axial scan of the Near Field Scanning Optical Microscopy fibre. The phase measurements accuracy is equivalent to lambda/60 when the measurement is performed in air. The method capability is demonstrated on an Achroplan x20 microscope objective with 0.4 numerical aperture. A more complete study on a x100 microscope objective with 1.3 numerical aperture is also presented, in which measurements performed with our setup are compared with the prediction of an analytical aberrations model.

Analysis of optical systems with extended depth of field using the Wigner distribution function

We describe the use of a Wigner distribution function approach for exploring the problem of extending the depth of field in a hybrid imaging system. The Wigner distribution function, in connection with the phase-space curve that formulates a joint phase-space description of an optical field, is employed as a tool to display and characterize the evolving behavior of the amplitude point spread function as a wave propagating along the optical axis. It provides a comprehensive exhibition of the characteristics for the hybrid imaging system in extending the depth of field from both wave optics and geometrical optics. We use it to analyze several well-known optical designs in extending the depth of field from a new viewpoint. The relationships between this approach and the earlier ambiguity function approach are also briefly investigated.

Manufacture of pupil filters for 3D beam shaping

In a previous work we presented a new method for binarizing pupil filters designed to control the three-dimensional (3D) irradiance distribution in the focal volume of apodized systems. The method is based in the fact that the 3D amplitude point spread function of an axially-symmetrical system can be recovered entirely from a one-dimensional (1D) set of regularly spaced amplitude samples. Hence we proposed the use of 1D iterative Fourier transform algorithm to binarize a, properly mapped, version of the amplitude transmittance of the filter. The binary masks obtained consist of a set of opaque and transparent concentric annular zones. In this paper we have built two of these masks with opposing properties and we have experimentally verified their abilities in a focusing system. These experimental results strongly agree previous theoretical predictions.

Point-spread function reconstruction in high aperture lenses focusing ultra-short laser pulses

In this paper we discuss the measurement of the amplitude point-spread function (PSF) of high aperture lenses focusing ultrashort laser pulses. In the experimental set-up a Twyman–Green interferometer and an autocorrelator are combined to function as a phase-shifting interferometer which is then used to measure the phase distribution in the pupil plane of the lens. Numerical reconstruction of the interferograms permits us to calculate the spatial distribution of the amplitude and phase of the point-spread function. Our work is relevant for cases when ultra-short laser pulses are focused for applications such as two- and three-photon fluorescence, second- and third-harmonic generation microscopy, optical coherence tomography and microscopy, and optical data storage.

The measurement of the amplitude point spread function of microscope objective lenses

We present a simple method of directly measuring the complex amplitude point spread function of a microscope objective lens. The method is based on an optical fibre interferometer. Experimental results are presented for a high‐aperture water‐immersion objective lens.

Analysis of confocal microscopy under ultrashort light-pulse illumination: comment

We show that the three-dimensional (3-D) amplitude point-spread function (APSF) under ultrashort light-pulse illumination reported by Kempe and Rudolph [ J. Opt. Soc. Am. A10, 240 ( 1993)] neglects some factors. A complete expression for the 3-D APSF for general cases is given.

Analysis of confocal microscopy under ultrashort light-pulse illumination: reply to comment

The importance and physical meaning of the terms neglected in the amplitude point-spread function in J. Opt. Soc. Am. A10, 240 ( 1993) are discussed.

Vector Wave Imagery with a Lens Masked by Polarizers

Abstract The optical transfer function (OTF) of an imaging system using polarization devices depends in general on the state of polarization of the input beam. In fact, the ‘amplitude point spread function’ (APSF) of such a system is different for different linearly polarized components of the input beam. This implies that the APSF of a system using polarizing devices behaves as a vector quantity. The nature of the final image is determined by the relative contribution of the two components of the vector APSF. The specific imaging system considered in the present study consists of a circularly symmetric polarization mask with linear polarizers having different orientations for the central circular and annular regions of an ideal lens aperture. If the light originating from an object point is in general elliptically polarized, the OTF of such a system with an analyser at the output is seen to have three additive components, which are, in fact, the Fourier coefficients of the OTF which varies periodically w...

Speckle intensity mean value dependence on the number of scatterers

The number of scatterers contributing to the speckle amplitude can be determined by the spot size of the incident light or by the amplitude point spread function of the optical system. The speckle intensity mean value measurement results with two methods of choosing the number of scatterers applied are presented. The values of the rms phase deviation and correlation length obtained from two methods agree well. The properties of both methods are discussed. The possibilities for the roughness measurement are suggested.

A contrast variation of image speckle intensity under illumination of partially coherent light

Speckle patterns are formed by completely and partially coherent light at the image plane of a diffusing object. The general formula is derived for the contrast variation of the image speckle intensity distribution as a function of the spatial coherence of the illuminating light, the amplitude point-spread function of the optical imaging system and the statistical characteristic of the diffusing object. The effect of spatial coherence of the illuminating light on the contrast variations of the image speckle intensity distribution is theoretically evaluated under various statistical conditions of the diffusing object. The theoretical results are confirmed experimentally.