DOCSLIB.ORG

Nanophotonics Enhanced Coverslip for Phase Imaging in Biology Lukas Wesemann1,2, Jon Rickett1, Jingchao Song1, Jieqiong Lou1, Elizabeth Hinde1, Timothy J

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Nanophotonics Enhanced Coverslip for Phase Imaging in Biology Lukas Wesemann1,2, Jon Rickett1, Jingchao Song1, Jieqiong Lou1, Elizabeth Hinde1, Timothy J Wesemann et al. Light: Science & Applications (2021) 10:98 Official journal of the CIOMP 2047-7538 https://doi.org/10.1038/s41377-021-00540-7 www.nature.com/lsa LETTER Open Access Nanophotonics enhanced coverslip for phase imaging in biology Lukas Wesemann1,2, Jon Rickett1, Jingchao Song1, Jieqiong Lou1, Elizabeth Hinde1, Timothy J. Davis1 and Ann Roberts 1,2 Abstract The ability to visualise transparent objects such as live cells is central to understanding biological processes. Here we experimentally demonstrate a novel nanostructured coverslip that converts phase information to high-contrast intensity images. This compact device enables real-time, all-optical generation of pseudo three-dimensional images of phase objects on transmission. We show that by placing unstained human cancer cells on the device, the internal structure within the cells can be clearly seen. Our research demonstrates the significant potential of nanophotonic devices for integration into compact imaging and medical diagnostic devices. Introduction Theinventionofthephase-contrastmicroscopebyFrits Phase-contrast microscopy has had a profound impact on Zernike14 earned him the Nobel Prize for Physics in 1953. biology, enabling weakly absorbing microscopic organisms The invention came from Zernike’sanalysisofthephase to be observed without staining or fixing1. Recently, profile of light that he describesasasumofplanewaves fi 15 1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; nanostructured thin- lm devices have been developed with travelling in different directions . The absence of intensity the potential to replace the bulky optics used in traditional contrast results from an ideal convolution of all the plane phase-contrast microscopes. These devices perform mathe- wave components, such that a perturbation to any one of matical operations on wavefields, such as first- and second- them disrupts the convolution creating contrast. The same – order differentiation2 4, and have been used to enhance the concept underpins X-ray phase-contrast imaging with dif- – edges of features in optical amplitude and phase images5 13. fracting crystals that modify the components of the incident – Unlike edge-detection that is easily performed digitally, wave according to their angles of incidence16 18. Similarly, phase visualisation requires processing prior to or at the phase contrast arises on wave propagation far from a phase point of measurement. Here we demonstrate a thin-film object where the propagating wave components experience device, a nanophotonics enhanced coverslip (NEC), that different phase shifts and interfere19, an effect exploited in – generates high-contrast images of pure phase objects on the transport of intensity method20 23. More generally, the transmission. We discuss the underlying principle and phase-contrast mechanism spatially filters the light in an demonstrate the device experimentally by imaging the optical system and can be described by an optical transfer internal structure of human cancer cells (HeLa). Our work function24. highlights the potential of nanophotonic devices in highly The optical transfer function (OTF), which maps the compact phase-imaging systems. incident light field to the transmitted light, can be used to understand how a nanophotonic device can create phase 25 contrast . Consider a simple one-dimensional OTF MðkxÞ that depends on the projection kx of the incident wavevector Correspondence: Lukas Wesemann ([email protected])or across the surface of the device. A pure phase wavefield E(x, ϕ Ann Roberts ([email protected]) z = 0) = ei (x) incident on the surface at z = 0isexpanded 1School of Physics, University of Melbourne, Melbourne, VIC 3010, Australia R ikxx 2ARC Centre of Excellence for Transformative Meta-Optical Systems, School of as a sum of plane waves Eðx; 0Þ¼ aðkxÞe dkx.The Physics, University of Melbourne, Melbourne, VIC 3010, Australia © The Author(s) 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a linktotheCreativeCommons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Wesemann et al. Light: Science & Applications (2021) 10:98 Page 2 of 6 ϕ intensity of this wave I(x,0) = |ei (x)|2 = 1showsnocontrast. interference and inhibiting transmission. Changing the ThenanophotonicdevicemodiR fiesthewaveinFourierspace incidence angle alters the phase relationship between the ikxx according to Emðx; 0Þ¼ aðkxÞMðkxÞe dkx.Closeto beams leading to incomplete cancellation of the transmitted = kx 0 it is alwaysP possible to expand the OTF in a power light. In this way, the device blocks the unscattered light Mð Þ¼ 1 n series kx n¼0 mnkx .Thetermm0 multiplies that from a sample but progressively transmits all other com- part of the wave unperturbed by the sample whereas the ponents as their incidence angles, or equivalently their fi term m1 linear in kx ÂÃrepresents theR rst derivative spatial frequencies, increase. iϕðxÞ ikxx of the phase profile, d e =dx ¼ ikxaðkxÞe dkx ¼ We fabricated the NEC with the geometry in Fig. 1b, using iϕðxÞ ie dϕðxÞ=dx.Whenmn = 0foralln ≠ 1theintensity electron beam lithography (see ‘Methods’ section) and I = |dϕ(x)/dx|2 exhibits phase contrast proportional to characterised its response numerically and experimentally. phase gradients in the wavefield. In this way, a spatial- The grating was overcoated with PMMA to inhibit oxidation frequency filter converts phase differences into intensity and to avoid contamination by the sample. The waveguide contrast. Likewise, higher-order terms in kx lead to combi- thicknessissuchthatitsupportsonlythefundamental nations of higher-order phase derivatives that also yield waveguidemode.Theoperationofthedevicewasmodelled contrast.ThisissimilartoZernike’s method in whichpffiffiffiffiffiffiffi the using the finite element method (FEM) in COMSOL Mul- filtering property is such that m0 = 1andmn ¼ i ¼ À1 tiphysics that includes the polarisation dependence. The for n > 0 that shifts the phase of the diffracted wave by 90°15. optical properties for silver were taken from Johnson and 27 Christy and the refractive index of a TiO2 thin-film similar Results to that used in the waveguide layer was measured experi- Our nanophotonic device exploits the contrast-forming mentally yielding a value nwg = 2.25 at λ = 633 nm. The properties of spatial-frequency filters to reject the calculated electric field distribution for normally incident unscattered wave components from a sample but transmit light polarised parallel to the stripes (Fig. 1b) shows the those components with non-zero phase gradients. Sensi- standing waveguide mode and no transmission. The spec- tivity to propagation direction is achieved with a buried trum (Fig. 1c) has a broad resonance at λ = 650 nm where waveguide that samples and interferes each wavefront transmission is inhibited. At this wavelength, the OTF over a large distance across the surface (Fig. 1a). (Fig. 1d) also shows that normally incident light is blocked Light is coupled into and out of the waveguide by a dif- but that the intensity of light transmitted increases with fraction grating, composed of metal stripes, where the increasing spatial-frequency kx across the surface for s- grating is diffracting into only the higher refractive index of polarisation, as required for phase-contrast imaging. In the waveguide layer26. Light incident between the stripes is addition, the device exhibits a phase transfer function that diffracted into three beams—a zero-order diffracted beam varies within a limited range of approximately π/2, which is (n = 0) that propagates in the incident direction and two important to avoid artefacts in processed images. Here we first-order beams (n = ±1)trappedinthewaveguide.On focus our discussion on s-polarised illumination, where the reaching the metal stripes, the n = ±1 beams reflect with a device exhibits stronger angular sensitivity than for p- π phase shift and diffract to reform the original zero-order polarisation. High-pass spatial-frequency filtering using this beam. This reformed beam propagates in parallel with the device is also reproduced by the simple model in the Sup- incident light but out of phase, resulting in destructive plementary Information, which supports our understanding. abcz d 1 1 1 1 PMMA p Ag t2 2 0.8 0.8 0.8 0.5 d k TiO2 t1 NEC 0.6 0.6 0.6 rad] kz SiO2 0 x incident light Emax 0.4 0.4 abs(t) 0.4 Reflectance kx –0.5 arg(t) [ y Ag Ag Ag Ag Z Ey Transmittance |t| 0.2 0.2 0.2 Y 0 0 –1 E 0 X min 610 620 630 640 650 660 670 680 –0.1 –0.05 0 0.05 0.1 [nm] kx/k0 Fig. 1 The nanophotonics enhanced coverslip (NEC) and simulations of its performance. a A sketch of the NEC showing the geometry and the incident wave vectors. b A cross-section used in a FEM simulation and the calculated electric field distribution (ŷ component) for normally incident light at a wavelength λ = 650 nm, showing the standing wave induced in the waveguide. The design parameters are t1 = 100 nm, t2 = 40 m, d = 200 nm and p = 400 nm. c The calculated frequency response for transmission and reflection of normally incident light identifying the resonance at λ = 650 nm. d The calculated complex optical transfer function for s-polarised light Mðkx Þ at the resonance wavelength λ = 650 nm, expressed as a modulation transfer function jjMðkxÞ and a phase transfer function arg Mðkx Þ Wesemann et al. Light: Science & Applications (2021) 10:98 Page 3 of 6 Input 1 1 a LP c d b 0.9 ky=0 0.8 0.8 1 2 | | ) ) x 0.7 x =0 x H(k H(k 0.6 0.6 | k | y-pol NA=0.4 y NEC 0.5 0.4 0.4 Norm.
Load more

Recommended publications
  • Precise and Fast Spatial-Frequency Analysis Using the Iterative Local Fourier Transform
    Vol. 24, No. 19 | 19 Sep 2016 | OPTICS EXPRESS 22110 Precise and fast spatial-frequency analysis using the iterative local Fourier transform 1 2 2,* SUKMOCK LEE, HEEJOO CHOI, AND DAE WOOK KIM 1Department of Physics, Inha University, Incheon, 402-751, South Korea 2College of Optical Sciences, University of Arizona, 1630 East University Boulevard, Tucson, Arizona 85721, USA *[email protected] Abstract: The use of the discrete Fourier transform has decreased since the introduction of the fast Fourier transform (fFT), which is a numerically efficient computing process. This paper presents the iterative local Fourier transform (ilFT), a set of new processing algorithms that iteratively apply the discrete Fourier transform within a local and optimal frequency domain. The new technique achieves 210 times higher frequency resolution than the fFT within a comparable computation time. The method’s superb computing efficiency, high resolution, spectrum zoom-in capability, and overall performance are evaluated and compared to other advanced high-resolution Fourier transform techniques, such as the fFT combined with several fitting methods. The effectiveness of the ilFT is demonstrated through the data analysis of a set of Talbot self-images (1280 × 1024 pixels) obtained with an experimental setup using grating in a diverging beam produced by a coherent point source. ©2016 Optical Society of America OCIS codes: (300.6300) Spectroscopy, Fourier transforms; (070.4790) Spectrum analysis; (070.6760) Talbot and self-imaging effects. References and links 1. L. M. Sanchez-Brea, F. J. Torcal-Milla, J. M. Herrera-Fernandez, T. Morlanes, and E. Bernabeu, “Self-imaging technique for beam collimation,” Opt. Lett. 39(19), 5764–5767 (2014).
    [Show full text]
  • Fourier Optics
    Fourier Optics 1 Background Ray optics is a convenient tool to determine imaging characteristics such as the location of the image and the image magni¯cation. A complete description of the imaging system, however, requires the wave properties of light and associated processes like di®raction to be included. It is these processes that determine the resolution of optical devices, the image contrast, and the e®ect of spatial ¯lters. One possible wave-optical treatment considers the Fourier spectrum (space of spatial frequencies) of the object and the transmission of the spectral components through the optical system. This is referred to as Fourier Optics. A perfect imaging system transmits all spectral frequencies equally. Due to the ¯nite size of apertures (for example the ¯nite diameter of the lens aperture) certain spectral components are attenuated resulting in a distortion of the image. Specially designed ¯lters on the other hand can be inserted to modify the spectrum in a prede¯ned manner to change certain image features. In this lab you will learn the principles of spatial ¯ltering to (i) improve the quality of laser beams, and to (ii) remove undesired structures from images. To prepare for the lab, you should review the wave-optical treatment of the imaging process (see [1], Chapters 6.3, 6.4, and 7.3). 2 Theory 2.1 Spatial Fourier Transform Consider a two-dimensional object{ a slide, for instance that has a ¯eld transmission function f(x; y). This transmission function carries the information of the object. A (mathematically) equivalent description of this object in the Fourier space is based on the object's amplitude spectrum ZZ 1 F (u; v) = f(x; y)ei2¼ux+i2¼vydxdy; (1) (2¼)2 where the Fourier coordinates (u; v) have units of inverse length and are called spatial frequencies.
    [Show full text]
  • The Representation of Complex Images in Spatial Frequency Domains of Primary Visual Cortex
    9310 • The Journal of Neuroscience, August 29, 2007 • 27(35):9310–9318 Behavioral/Systems/Cognitive The Representation of Complex Images in Spatial Frequency Domains of Primary Visual Cortex Jing X. Zhang,1 Ari Rosenberg,2 Atul K. Mallik,3 T. Robert Husson,2 and Naoum P. Issa4 1Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, and 2Committee on Computational Neuroscience, 3Committee on Neurobiology, and 4Department of Neurobiology, University of Chicago, Chicago, Illinois 60637 The organization of cat primary visual cortex has been well mapped using simple stimuli such as sinusoidal gratings, revealing superim- posed maps of orientation and spatial frequency preferences. However, it is not yet understood how complex images are represented across these maps. In this study, we ask whether a linear filter model can explain how cortical spatial frequency domains are activated by complex images. The model assumes that the response to a stimulus at any point on the cortical surface can be predicted by its individual orientation, spatial frequency, and temporal frequency tuning curves. To test this model, we imaged the pattern of activity within cat area 17 in response to stimuli composed of multiple spatial frequencies. Consistent with the predictions of the model, the stimuli activated low and high spatial frequency domains differently: at low stimulus drift speeds, both domains were strongly activated, but activity fell off in high spatial frequency domains as drift speed increased. To determine whether the filter model quantitatively predicted the activity patterns, we measured the spatiotemporal tuning properties of the functional domains in vivo and calculated expected response ampli- tudes from the model.
    [Show full text]
  • Vision: from Eye to Brain (Chap 3, Part B)
    Vision: From Eye to Brain (Chap 3, Part B) Lecture 7 Jonathan Pillow Sensation & Perception (PSY 345 / NEU 325) Princeton University, Spring 2015 1 more “channels”: spatial frequency channels spatial frequency: the number of cycles of a grating per unit of visual angle (usually specified in degrees) • think of it as: # of bars per unit length low frequency intermediate high frequency 2 Why sine gratings? • Provide useful decomposition of images Technical term: Fourier decomposition 3 Fourier decomposition • mathematical decomposition of an image (or sound) into sine waves. reconstruction: “image” 1 sine wave 2 sine waves 3 sine waves 4 sine waves 4 “Fourier Decomposition” theory of V1 claim: role of V1 is to do “Fourier decomposition”, i.e., break images down into a sum of sine waves • Summation of two spatial sine waves • any pattern can be broken down into a sum of sine waves 5 Fourier decomposition • mathematical decomposition of an image (or sound) into sine waves. Original image High Frequencies Low Frequencies 6 original low medium high 7 Retinal Ganglion Cells: tuned to spatial frequency Response of a ganglion cell to sine gratings of different frequencies 8 The contrast sensitivity function Human contrast sensitivity illustration of this sensitivity 9 Image Illustrating Spatial Frequency Channels 10 Image Illustrating Spatial Frequency Channels 11 If it is hard to tell who this famous person is, try squinting or defocusing “Lincoln illusion” Harmon & Jules 1973 12 “Gala Contemplating the Mediterranean Sea, which at 30 meters becomes
    [Show full text]
  • Visual Performance Theoretical Limit of Resolution
    Visual Performance Aspects Conditions • Resolution Limit • Illumination • Pattern Detection • Monocular vs. Binocular • Pattern Recognition • Distance • Contrast Level • On-axis vs. Off-axis • Color • Single or multiple targets • Temporal Response • Literacy & Verbal ability Theoretical Limit of Resolution θ Rayleigh Criterion 1.22λ θ = radians D For λ = 587.6 nm D ranges from 2 – 8 mm 0.090 ≤θ≤0.358 mrad 0.3 ≤θ≤1.23 minutes of arc 1 Rayleigh Criteria 1 1.6 mm Pupil 0.75 Contrast 14% Airy #1 0.5 Airy #2 Sum Relative Irradiance 0.25 Photorecptor Photorecptor Photorecptor 0 -15 -10 -5 0 5 10 15 20 25 Position (microns) Visual Acuity Visual Acuity is a measure of the smallest detail that can be resolved by the visual system. There are different types of acuity measures. Point Acuity – “Binary Star” test – typically 1 arcmin resolution Vernier Acuity – Two lines slightly offset from each other. Finds smallest detectable offset – typically 10 seconds of arc θ 2 Visual Acuity Grating Acuity – Sinusoidal or Square wave gratings are used to determine the smallest separation between peaks that can be resolved. Typically 2 arcmin. θ Visual Acuity Letter Acuity – Different Letters or Symbols need to be recognized Typically 5 arcmin. E θ F P T O Z L P E D ETDRS Landolt C Tumbling Es Lea 3 Visual Acuity & Pupil Size Visual Acuity Charts 5’ N Visual Acuity Charts are designed so the 20/20 line subtends 5 arcmin. 20/40 subtends 10 arcmin 20/10 subtends 2.5 arcmin 4 Stereo Acuity Given one object slightly closer than the other, find the smallest separation that is resolvable.
    [Show full text]
  • Psychophysical Aspects of Contrast Sensitivity*
    S Afr Optom 2013 72(2) 76-85 Psychophysical aspects of contrast sensitivity* Anusha Y Sukhaa and Alan Rubinb a, b Department of Optometry, University of Johannesburg, PO Box 524, Auckland Park, 2006 South Africa a<[email protected]> b<[email protected]> Received 23 November 2012; revised version accepted 9 June 2013 Abstract demonstrate stereo-pair representation of contrast visual acuities in the context of diabetic eyes. This paper reviews the psychophysical aspects The doctoral research of the first author (AYS) of contrast sensitivity which concerns components that applies similar idea to understanding both of visual stimuli and the behavioural responses inter- and intra-ocular variation of contrast visual and methods used in contrast sensitivity testing. acuities. Some discussion is included of the different types of contrast sensitivity charts available as well Key words: contrast, contrast sensitivity, as a brief background on the different types of contrast visual acuity, vision science, vision graphical representations of contrast sensitivity psychophysics, stereo-pair scatter plots, and contrast visual acuities. Two illustrations also multivariate statistics Introduction (namely spatial frequency, contrast, spatial phase, and orientation) by means of Fourier analysis. Fourier Psychophysics is a scientific discipline designed analysis is an analytical method that calculates to measure internal sensory and perceptual responses simple sine-wave components whose linear sum to external stimuli1. Sensory stimuli and behavioural forms a given complex image2, 3. The visual stimuli responses are the defining or crucial concepts in typically used in contrast sensitivity testing consist of determining contrast thresholds (for example, visual sine-wave or square-wave gratings whose luminance stimuli are used in chart-based contrast sensitivity perpendicular to the bars is modulated in sinusoidal measurements).
    [Show full text]
  • A Tutorial Essay on Spatial Filtering and Spatial Vision
    Spatial Filters/Meese/Nov 2000 A Tutorial Essay on Spatial Filtering and Spatial Vision Tim S Meese Neurosciences School of Life and Health Sciences Aston University Feb 2009: minor stylistic and modifications and technical corrections March 2009: referencing tidied up To follow: Final round-up sections and detailed references added. -1- Spatial Filters/Meese/Nov 2000 1. Introduction To the layperson, vision is all about ‘seeing’—we open our eyes and effortlessly we see the world ‘out there’. We can recognize objects and people, we can interact with them in sensible and useful ways and we can navigate our way about the environment, rarely bumping into things. Of course, the only information that we are really able to act upon is that which is encoded as neural activity by our nervous system. These visual codes, the essence of all of our perceptions, are constructed from information arriving from each of two directions. Image data arrives ‘bottom-up’ from our sensory apparatus, and knowledge-based rules and inferences arrive ‘top-down’ from memory. These two routes to visual perception achieve very different jobs. The first route is well suited to providing a descriptive account of the retinal image while the second route allows these descriptions to be elaborated and interpreted. This chapter focuses primarily on one aspect of the first of these routes, the processing and encoding of spatial information in the two-dimensional retinal image. One of the major success stories in understanding the human brain has been the exploration of the bottom-up processes used in vision, sometimes referred to as early vision.
    [Show full text]
  • Session 2. (1) Spatial Frequency and Fourier Transformation
    2005 Autumn semester Pattern Information Processing Topic 1. Sampling and digital processing of images Session 2. (1) Spatial frequency and Fourier transformation Organization of digital images is explained in this Diffraction of light and imaging and the next sessions. Although an image is natu- We start from the optical phenomenon of imaging. rally a continuous distribution of brightness, it has to The imaging is defined as a collection of diverged be converted into a discrete set of integers for com- light spread from a point of object into one point by puter processing. The conversion into discrete pixels a lens. This phenomenon can be observed from the is called sampling, and the conversion into integers following point of view: The light has the property of is called quantization. The sampling period is quite diffraction. The diffraction of wave is a phenomenon important issue, and it is evaluated by the concept of that the wave reaches beyond an opaque object ob- spatial frequency. The concept of spatial frequency stracting its path. For example, even if the progress and Fourier transformation are explained in this ses- of wave on a water surface is obstructed by a board, sion. it reaches beyond the board. Since the light is a kind of electromagnetic wave, the light has this property. The radio wave reaches beyond obstructing objects from the broadcasting station by diffraction. wavefronts reach beyond divergence of light the obstruction collection of light Opaque object wavefronts Fig. 2: Diffraction. Fig. 1: Imaging. If the light passes through a diffraction grating, of first order, is obtained in this direction.
    [Show full text]
  • Contrast Sensitivity and Spatial Frequency Response of Primate Cortical Neurons in and Around the Cytochrome Oxidase Blobs DAVID P
    Vision Res. Vol. 35, No. 11, pp. 1501-1523, 1995 Pergamon Copyright © 1995 Elsevier Science Ltd 0042-6989(94)00253-3 Printed in Great Britain. All rights reserved 0042-6989/95 $9.50 + 0.00 Contrast Sensitivity and Spatial Frequency Response of Primate Cortical Neurons in and Around the Cytochrome Oxidase Blobs DAVID P. EDWARDS,* KEITH P. PURPURA,*t EHUD KAPLAN*:~ Received 26 January 1994; in revised form 26 September 1994 The striate cortex of macaque monkeys contains an array of patches which stain heavily for the enzyme cytochrome oxidase (CO blobs). Cells inside and outside these blobs are often described as belonging to two distinct populations or streams. In order to better understand the function of the CO blobs, we measured the contrast sensitivity and spatial frequency response of single neurons in and around the CO blobs. Density profiles of each blob were assessed using a new quantitative method, and correlations of local CO density with the physiology were noted. We found that the CO density dropped off gradually with distance from blob centers: in a typical biob the CO density dropped from 75% to 25% over 100 pm. Recordings were confined to cortical layers 2]3. Most neurons in these layers have poor contrast sensitivity, similar to that of the parvocellular neurons in the lateral geniculate nucleus. However, in a small proportion of layers 2]3 neurons we found higher contrast sensitivity, similar to that of the magnocellular neurons. These neurons were found to cluster near blob centers. This finding is consistent with (indirect) parvocellular input spread uniformly throughout layers 2/3, and (indirect) magnoceHular input focused on CO blobs.
    [Show full text]
  • Nanophotonics in Microscopy
    Lecture 12 – Nanophotonics in Microscopy EECS 598-002 Winter 2006 Nanophotonics and Nano-scale Fabrication P.C.Ku Schedule for the rest of the semester Introduction to light-matter interaction (1/26): How to determine ε(r)? The relationship to basic excitations. Basic excitations and measurement of ε(r). (1/31) Structure dependence of ε(r) overview (2/2) Surface effects (2/7): Surface EM wave Surface polaritons Size dependence Case studies (2/9 – 2/16): Quantum wells, wires, and dots Nanophotonics in microscopy Nanophotonics in plasmonics Dispersion engineering (2/21 – 3/7): Material dispersion Waveguide dispersion (photonic crystals) EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 2 Principles of optical microscopy The information contained in the object/image is carried by the light wave to the detector (e.g. eyes). Information = F(x,y) Æ F(,kkxy ) EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku 3 Optical vs electron microscopy Advantages of optical microscopes Photon energy is low (~ eV). Electron energy is high (~10-100 keV) -27 Photon momentum is low (~ 10 kg m/s). Electron momentum is high (~ 10-23 -10-22 kg m/s) Especially good to study optical processes (including nonlinear optical response) in the sample Ultra-short optical pulse is available to study ultra-fast processes Can make the fluorescence work Æ useful for biological imaging Disadvantages of optical microscopes Photon does not have charge. Cannot study the Coulomb interaction in the sample. Photon does not reveal information regarding the chemical composition of the sample (unless we go to the x-ray wavelength).
    [Show full text]
  • Standards for Visual Acuity June 15, 2006 Page 1
    Standards for Visual Acuity June 15, 2006 Page 1 Standards for Visual Acuity A Report Prepared For Elena Messina Intelligent Systems Division National Institute for Standards and Technology In Support Of ASTM International Task Group E54.08.01 On Performance Measures for Robots for Urban Search and Rescue Prepared by John M Evans LLC Newtown, CT [email protected] Under Contract 2006-02-13-01 Through KT Consulting Standards for Visual Acuity June 15, 2006 Page 2 Standards for Visual Acuity 1. Summary Visual acuity is defined as the ability to read a standard test pattern at a certain distance, usually measured in terms of a ratio to “normal” vision. Multiple standard test patterns have been developed and are in use today. Closely related are measures of image quality or imaging or printing system quality, generally referred to as optical resolution. Again, standard test patterns can be used, or the modulation transfer function (MTF) can be measured. The MTF defines the ability of an imaging system to reproduce a given spatial frequency; the MTF of components of a system can be multiplied to give the MTF of the composite system. The problem for defining the quality of vision systems for robots for application in Urban Search and Rescue (USAR) involves viewing a scene with a camera (which includes a lens and sensor chip and digitization circuitry), transmission of the digital data and conversion to an image on a screen that can be viewed by the operator. Hence, either approach is relevant. We will discuss both approaches with emphasis on the first.
    [Show full text]
  • Plasmonic Superlens Imaging Enhanced by Incoherent Active Convolved Illumination
    Plasmonic Superlens Imaging Enhanced by Incoherent Active Convolved Illumination Wyatt Adams, Anindya Ghoshroy, and Durdu O.¨ G¨uney∗ Department of Electrical and Computer Engineering, Michigan Technological University, Houghton, MI 49931-1295, USA E-mail: [email protected] Abstract We introduce a loss compensation method to increase the resolution of near-field imaging with a plasmonic superlens that relies on the convolution of a high spatial frequency passband function with the object. Implementation with incoherent light removes the need for phase information. The method is described theoretically and numerical imaging results with artificial noise are presented, which display enhanced resolution of a few tens of nanometers, or around one-fifteenth of the free space wave- length. A physical implementation of the method is designed and simulated to provide a proof-of-principle, and steps toward experimental implementation are discussed. Keywords arXiv:1801.06583v1 [physics.optics] 19 Jan 2018 plasmonics, superresolution, metamaterials, loss compensation, near-field imaging The theory and experimental demonstration of metamaterials has inspired interesting avenues of imaging,1{12 lithography,13,14 and beam generation15 beyond the diffraction limit, particularly motivated by the prospect of a perfect lens.16 Researchers have quickly realized 1 superlenses,1{6,13,14 hyperlenses,7{10 integrated metalenses,11,15 and non-resonant elliptical lenses,12 which can either amplify or propagate evanescent waves carrying the precious high spatial frequency information of an object. However, these efforts have stopped short of creating a truly perfect lens, since their resolution is limited by losses and they cannot focus light of arbitrary polarization especially at optical wavelengths.
    [Show full text]