Optical transfer function analysis of circular-pupil wavefront coding systems with separable phase masks

Transfer function estimation of turboalternator from practical operating data by spectral analysis

: The end-to-end performance achieved by an adaptive optical (AO) imaging system is determined by a combination of the residual time-varying phase distortions associated with atmospheric turbulence, and the quasi-static unsensed and uncorrectable aberrations in the optical system itself. Although the effects of these two errors on the time averaged Strehl ratio and the time averaged optical transfer function (OTF) of the AO system are not formally separable, such an approximation is found to be accurate to within a few per cent for a range of representative residual wave-front errors. In these calculations, we have combined static optical system aberrations and time-varying residual phase distortion characteristic of deformable mirror (DM) fitting error, wave-front sensor (WFS) noise, and anisoplanatism. The static aberrations consist of focus errors of varying magnitudes as well as a combination of unsensed and uncorrectable mirror figure errors derived from modeling by the Gemini beta-meter Telescopes project. The overall Strehl ratios and OTF's due to the combined effect of these error sources are well approximated as products of separate factors for the static and time-varying aberrations, as long as the overall Strehl ratio due to both errors is greater than about 0.1. For lower Strehl ratios the products provide lower bounds on the actual values of the Strehl ratio and OTF. The speckle transfer function (STF) is also well approximated by a product of two functions, but only where AO compensation is sufficiently good that speckle imaging techniques are usually not required.

Image restoration of the open-loop adaptive optics retinal imaging system based on optical transfer function analysis

I investigate the optical transfer function of three-dimensional display systems. Moreover, I obtain an average sampled modulation transfer function describing discrete, sampled display systems and show that in the proper limit of geometrical optics it is equivalent to the shift-invariant optical transfer function. I apply the theory to describe holographic stereograms and discuss the effects of amplitude and phase filters on the optical resolution.

The optical transfer function (OTF) of an IR imaging system using coherent (laser) illumination was compared to its performance when imaging with incoherent (thermal) radiation. The imaging system under consideration is a basically passive framing infrared system in which the IR detector is scanned throughout an 8°x10° field of view (FOV) to develop an IR image. The system can be operated in the laser imaging (active) mode by synchronously scanning a CO2 laser beam with the detector. The linespread function method was used to derive the respective OTFs. From the measured lineshape response, the OTF was computed using Fast Fourier Transform (FFT) techniques. These measurements and analyses have shown that (1) the OTF is a valid and reproducible measure of the system's frequency response, even when coherent illumination is used, and (2) the active mode tended to give a reproducibly higher MTF than the passive mode for all wire targets used.

For (i), sufficiently small aberrations or (ii), arbitrary aberrations but a sufficiently small spatial frequency, the modulation and phase transfer functions of a lens system may be expressed as polynomials of the second degree in frequency. In this paper the coefficients of these polynomials are related to the aberrations of a lens system which in general does not have an axis of symmetry. Hence, under assumption (ii) the derived expressions for the modulation and phase transfer functions are applicable to any fabricated lens system, over a limited range of spatial frequencies. In addition, the coefficient of the linear term in the phase function expansion is shown to be the first moment of the spread function, and to be linear in its dependence on aberrations. Advantage may be taken of this relation between a physical observable (the first moment) and the aberrations by using it to generate a set of linear equations having only aberrations as unknowns. By its solution some aberrations of (a), axial sym...

Wavefront coding (WFC) is used to extend the field depth of an incoherent optical system by employing a phase mask on the pupil. We uses a Fisher information (FI) metric based optimization method to design a phase mask by taking the modulation transfer function (MTF) of the practical optical system into consideration. This method can modulate the wavefront so that the point spread function and optical transfer function are insensitive to the object distance. The simulation results show that the optimized phase mask based on the proposed method can further improve the defocusing image quality while maintaining the focusing image quality.

Several methods are available to measuring the presampled modulation transfer function (MTF) of a digital radiography system by using a slit camera, a slanted edge test device or a bar phantom. Many studies demonstrated the advantages of the edge method compared to the slit method. However, the method of processing to estimate the MTF is slightly different for each publication. The purpose of this study is to compare the effects of various processing steps with an edge image on estimating the presampled MTF. A digital image of a slanted edge test device was acquired and then examined using different image processing such as windowing the edge spread function (ESF), determining a region of interest (ROI) and locally smoothing the ESF data. The results of this study indicated that the impact of determining a ROI on the MTF is relatively modest and that the truncation of the ESF due to a finite window width causes an incorrect inflation error in the MTF estimate and loss of detail at high frequency. Moreover, the influence of ESF smoothing on the MTF is demonstrated, and more rigorous smoothing of the ESF produces a less noisy MTF and, consequently, a high data loss at high-frequency. In conclusion, an ESF processing technique can moderately impact the MTF estimates, and an adequate ROI and window width without a smoothing process is suggested.

Several microscope techniques namely confocal microscopy have a huge number of applications in metrology reported in literature. Although they are essentially imaging techniques metrology and particularly profilometry is a very attractive field of application owing to their ability to obtain depth discrimination. In recent years there has been a growth of three dimensional microscopy methods namely those based on structured incoherent illumination. In spite of different implementation approaches they are based on the fact that the optical transfer function (OTF) of the imaging system attenuates with defocus for every spatial frequency with the exception of zero-frequency. In this way it is able to get depth information through the projection of a grid structure so it is suitable for application in profilometry. The purpose of this work is to develop and test a profilometer based on a low-cost bench microscope. The optical layout is an epi-illuminated configuration of scanning-stage type for reflection microscopy. Tests with structured incoherent illumination in this case line-illumination are being carried out in order to achieve depth discrimination using a linear image sensor of CMOS type as detector. This paper presents a description of the optical arrangement as well as the acquisition and control system. Preliminary results are shown that were obtained using a plane mirror to measure its axial resolution and a micromachined component to test the application of this bench microscope in profilometry.

Structured illumination microscopy (SIM) is an attractive choice for fast super-resolution imaging. The generation of structured illumination patterns made by interference of laser beams is broadly employed to obtain high modulation depth of patterns, while the polarizations of the laser beams must be elaborately controlled to guarantee the high contrast of interference intensity, which brings a more complex configuration for the polarization control. The emerging pattern projection strategy is much more compact, but the modulation depth of patterns is deteriorated by the optical transfer function (OTF) of the optical system, especially in high spatial frequency near diffraction limit. Therefore, the traditional super-resolution reconstruction algorithm for interference-based SIM will suffer from much artifact in the case of projection-based SIM that possesses a low modulation depth. Here, we propose an alternative reconstruction algorithm based on image recombination transform (IRT), which provides an alternative solution to address this problem even in a weak modulation depth. We demonstrated the effectiveness of this algorithm in the multicolor super-resolution imaging of BPAE cells in our developed projection-based SIM system, which applies a computer controlled digital micro-mirror device (DMD) for fast fringe generation and multicolor LEDs for illumination. The merit of the system incorporated with the proposed algorithm allows for a low excitation intensity fluorescence imaging even less than 1W/cm2, which is beneficial for the long-term, in vivo super-resolved imaging of live cells and tissues.

We use aberration theory to derive a generalized pupil function of the Golay3 imaging system when astigmatisms exist in its submirrors. Theoretical analysis and numerical simulation using ZEMAX show that the point spread function (PSF) and the modulation transfer function (MTF) of the Golay3 sparse aperture system have a periodic change when there are piston errors. When the peak-valley value of the wavefront (PV(tilt)) due to the tilt error increases from zero to λ, the PSF and the MTF change significantly, and the change direction is determined by the location of the submirror with the tilt error. When PV(tilt) becomes larger than λ, the PSF and the MTF remain unvaried. We calculate the peaks of the signal-to-noise ratio (PSNR) resulting from the piston and tilt errors according to the Strehl ratio, and show that the PSNR decreases when the errors increase.

The presampling modulation transfer function (MTF) of a digital imaging system is commonly determined by measuring the system’s line spread function (LSF) using a narrow slit or differentiating the detector’s edge spread function (ESF) with an edge device. The slit method requires precise fabrication and alignment of a slit as well as a high radiation exposure. The edge method [3] is a complicated image processing procedure, requiring determination of the edge angle, reprojection, sub-binning, smoothing and differentiating the ESF, and spectral estimation. In this paper, a simple method is employed to evaluate the MTF using an edge device. The image processing procedures required by this method involve simply the determination of the over-sampling rate and the Fourier transform of the modified ESF. Differentiation and signal to noise ratio (SNR) improvement are jointly applied in the Fourier domain. The MTFs obtained by this simple method are compared to the theoretical MTF and the previously proposed more complicated edge method. The experimental results show that the proposed method provides a simple, accurate and convenient measurement of the presampling MTF for digital imaging systems.

The joint impact of atmospheric refraction and turbulence effects on the modulation transfer function (MTF) of an incoherent imaging system is analyzed using numerical simulations based on the brightness function technique. Atmospheric refractivity is described by a combination of the standard MUSA76 and inverse temperature layer (ITL) models, and atmospheric turbulence effects are accounted for using the classical Kolmogorov turbulence framework. We show that ITL-induced refractivity located in the vicinity of an air volume essential for image formation can create strongly spatially anisotropic phase aberrations, which may significantly impact imaging system performance. Numerical analysis demonstrates that these phase aberrations may change the image size, and cause spatial frequency shifts in observed images of horizontally oriented sine-patterns. Numerical simulations show the that combined effects of atmospheric turbulence and ITL-induced refractivity cause the MTF to be a nonlinear function that is dependent on the imaging system characteristics, propagation path geometry, and atmospheric turbulence and ITL-induced refractivity parameters.

On the dynamic system identification of the response behaviour of linear viscoelastic materials

In this paper,a refractive optical system with secondary image is adopted to realize 1. 67 F number and 4. 6 zoom ratio,and the ratio between the total length and focal length is 1,and the zooming lens group is driven by solenoid pilot actuated valve switching structure to complete zooming in 60 ms. In addition,an optical passive compensation method is used to realize an athermalized design in the range of- 40 ~ + 50 ℃ by choosing proper optical and structural materials. The design results show that the optical system's modulation transfer function in each field is close to the diffraction limit at different temperatures under the characteristic frequency of 20 lp /mm and the system size is compact with fast FOV switching. Finally,it is proved that this dual-FOV infrared optical system can meet the requirements for application.