Characterization and correction of spherical aberration due to glass substrate in the design and fabrication of Fresnel zone lenses
TL;DR: Two novel schemes for correction of spherical aberration are proposed and studied and the accuracy of the proposed aberration correction schemes is validated.
Abstract: As with a conventional lens, a Fresnel zone lens (FZL) can be used to image objects at infinity or nearby In the latter case, the FZL converts a diverging spherical wavefront into a converging spherical wavefront The glass substrate on which the FZL is fabricated introduces spherical aberration resulting in a shift of the image plane and blurring of the image Two novel schemes for correction of this spherical aberration are proposed and studied in this paper To demonstrate them, FZLs are designed with and without aberration correction They are fabricated using electron beam direct writing The devices are evaluated and the accuracy of the proposed aberration correction schemes is validated
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TL;DR: In this paper, a random-like coded phase mask (CPM) is used to modulate light diffracted by a point object (pinhole) and the intensity pattern is recorded and composed as a point spread hologram (PSH).
Abstract: We present a lensless, interferenceless incoherent digital holography technique based on the principle of coded aperture correlation holography. The acquired digital hologram by this technique contains a three-dimensional image of some observed scene. Light diffracted by a point object (pinhole) is modulated using a random-like coded phase mask (CPM) and the intensity pattern is recorded and composed as a point spread hologram (PSH). A library of PSHs is created using the same CPM by moving the pinhole to all possible axial locations. Intensity diffracted through the same CPM from an object placed within the axial limits of the PSH library is recorded by a digital camera. The recorded intensity this time is composed as the object hologram. The image of the object at any axial plane is reconstructed by cross-correlating the object hologram with the corresponding component of the PSH library. The reconstruction noise attached to the image is suppressed by various methods. The reconstruction results of multiplane and thick objects by this technique are compared with regular lens-based imaging.
37 citations
TL;DR: In this paper, the authors used a randomly multiplexed bifocal binary diffractive Fresnel zone lenses fabricated using electron beam lithography for super-resolution 3D imaging.
Abstract: Fresnel incoherent correlation holography (FINCH) is a self-interference based super-resolution three-dimensional imaging technique. FINCH in inline configuration requires an active phase modulator to record at least three phase-shifted camera shots to reconstruct objects without twin image and bias terms. In this study, FINCH is realized using a randomly multiplexed bifocal binary diffractive Fresnel zone lenses fabricated using electron beam lithography. The object space is calibrated by axially scanning a point object along the optical axis and recording the corresponding point spread holograms (PSHs). An object is mounted within the calibrated object space, and the object hologram was recorded under identical experimental conditions used for recording the PSHs. The image of the object at different depths was reconstructed by a cross-correlation between the object hologram and the PSHs. Application potential including bio-medical optics is discussed.
34 citations
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TL;DR: The reconstruction results of multiplane and thick objects by this technique are compared with regular lens-based imaging.
Abstract: We present a lensless, interferenceless incoherent digital holography technique based on the principle of coded aperture correlation holography. The acquired digital hologram by this technique contains a three-dimensional image of some observed scene. Light diffracted by a point object is modulated using a random-like coded phase mask (CPM) and the intensity pattern is recorded and composed as a point spread hologram (PSH). A library of PSH is created using the same CPM by moving the pinhole to all possible axial locations. Intensity diffracted through the same CPM from an object placed within the axial limits of the PSH library is recorded by a digital camera. The recorded intensity this time is composed as the object hologram. The image of the object at any axial plane is reconstructed by cross-correlating the object hologram with the corresponding component of the PSH library. The reconstruction noise attached to the image is suppressed by various methods. The reconstruction results of multi-plane and thick objects by this technique are compared with regular lens-based imaging.
27 citations
TL;DR: This tutorial discusses one of the basic optical configurations of a lensless QPI technique based on the phase-retrieval algorithm andmented codes in Octave for image acquisition and automation using a web camera in an open source operating system are provided.
Abstract: Quantitative phase imaging (QPI) techniques are widely used for the label-free examining of transparent biological samples. QPI techniques can be broadly classified into interference-based and interferenceless methods. The interferometric methods which record the complex amplitude are usually bulky with many optical components and use coherent illumination. The interferenceless approaches which need only the intensity distribution and works using phase retrieval algorithms have gained attention as they require lesser resources, cost, space and can work with incoherent illumination. With rapid developments in computational optical techniques and deep learning, QPI has reached new levels of applications. In this tutorial, we discuss one of the basic optical configurations of a lensless QPI technique based on the phase-retrieval algorithm. Simulative studies on QPI of thin, thick, and greyscale phase objects with assistive pseudo-codes and computational codes in Octave is provided. Binary phase samples with positive and negative resist profiles were fabricated using lithography, and a single plane and two plane phase objects were constructed. Light diffracted from a point object is modulated by phase samples and the corresponding intensity patterns are recorded. The phase retrieval approach is applied for 2D and 3D phase reconstructions. Commented codes in Octave for image acquisition and automation using a web camera in an open source operating system are provided.
18 citations
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TL;DR: In this article, a modified hologram reconstruction mechanism is presented which introduces the single shot capability in Fresnel incoherent correlation holography (FINCH) in inline configuration requires an active phase modulator and at least three camera shots to reconstruct objects without the twin image and bias terms.
Abstract: Fresnel incoherent correlation holography (FINCH) is a self-interference based super-resolution three-dimensional imaging technique. FINCH in inline configuration requires an active phase modulator and at least three camera shots to reconstruct objects without the twin image and bias terms. In this study, FINCH is realized using a randomly multiplexed bifocal binary Fresnel zone lenses fabricated using electron beam lithography. A modified hologram reconstruction mechanism is presented which introduces the single shot capability in FINCH. A point spread hologram library was recorded using a point object located at different axial locations and an object hologram was recorded. The image of the object at different planes were reconstructed using decorrelation of the object hologram by the point spread hologram library. Application potential including bio-medical optics is discussed.
17 citations
Cites background from "Characterization and correction of ..."
...Earlier studies indicated that the exclusion of the thickness and refractive index of glass plates introduces substantial spherical aberration into the system resulting in a variation in the focal distances and blurring of the focal spot.(19) Two techniques have been proposed to avoid the spherical aberration....
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...The second Fresnel zone lens (FZL2) is designed for finite conjugate mode with u = z1 and v = z2/2.(19) The object wave is focused by FZL2 at z2/2 from the RMBDL....
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References
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TL;DR: The imaging properties of two types of modified Fresnel zone plate are calculated and compared with those of the equivalent normal zone plate, with particular reference to their use in soft X-ray microscopy as mentioned in this paper.
Abstract: The imaging properties of two types of modified Fresnel zone plate are calculated and compared with those of the equivalent normal zone plate, with particular reference to their use in soft X-ray microscopy. The modifications considered are (1) central obstruction of the zone plates, which improves the resolving power but also leads to loss in efficiency and to a higher fraction of the energy in the outer parts of the diffraction pattern; and (2) a central zone plate with first-order focal length ƒ surrounded by outer zones with third-order focal length ƒ. This gives improved resolution and higher focused energy, but a smaller depth of focus and increased background.
90 citations
TL;DR: In this paper, the design and fabrication of the static and dynamic, on-and off-axis Fresnel zone lenses as well as their optical and switching properties are presented, and the switching behavior of the dynamic lenses is studied.
Abstract: Static and dynamic Fresnel zone lenses were fabricated in quartz glass by means of microstructuring techniques. Two types of on-axis and offaxis lenses with different focal lengths and of different apertures were designed to operate at wavelengths of 1·52 μm and 633 nm. The blazed profile of the onaxis and off-axis lenses was approximated by up to 16 and up to four discrete levels respectively. Dynamic, that is electrically switchable, lenses have been realized by filling the structured surface with liquid crystal. The optical properties of the lenses, such as the focal spot sizes and the diffraction efficiencies, were investigated. Further the switching behaviour of the dynamic lenses was studied. The design and fabrication of the static and dynamic, on-and off-axis Fresnel zone lenses as well as their optical and switching properties will be presented.
60 citations
TL;DR: The spherical aberration introduced by the stratified structure of skin is calculated and how the confocal signal is affected when attempting to image at various depths within the dermis is shown.
Abstract: We consider various strategies for confocal imaging of human skin which seek to reduce the effects of the specimen-induced aberrations. We calculate the spherical aberration introduced by the stratified structure of skin and show how the confocal signal is affected when attempting to image at various depths within the dermis. Using simple methods it is shown how images might be improved by compensating for the induced aberration. The methods include the use of an iris to reduce the pupil area, changing the refractive index of the immersion medium and using a lens with variable coverglass correction.
58 citations
"Characterization and correction of ..." refers methods in this paper
...The glass substrate aberration correction can be carried out using a predistortion pattern [16,17], by varying the pupil size of the objective lens [18]....
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TL;DR: The method is based on inverse ray tracing and can generate correction phase patterns whose peak-to-valley values are minimized and is useful in cases where a large phase modulation is needed, such as when employing a high-NA lens or focusing a beam deep inside a sample.
Abstract: We propose a simple method to correct a large amount of spherical aberration caused by a refractive index mismatch The method is based on inverse ray tracing and can generate correction phase patterns whose peak-to-valley values are minimized We also demonstrated spherical aberration correction in a transparent acrylic block using a liquid-crystal-on-silicon spatial light modulator (LCOS-SLM) A distorted focal volume without correction was substantially improved with correction This method is useful in cases where a large phase modulation is needed, such as when employing a high-NA lens or focusing a beam deep inside a sample
54 citations
"Characterization and correction of ..." refers methods in this paper
...The glass substrate aberration correction can be carried out using a predistortion pattern [16,17], by varying the pupil size of the objective lens [18]....
[...]