Introduction to Radio Interferometers
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Interferometric Spectrometers
LBNL-40663 UC-410 . ERNEST ORLANDO LAWRENCE BERKELEY NATIONAL LABORATORY Interferometric Spectrometers Anne Thome and Malcolm Howells Accelerator and Fusion Research Division June 1997 To be published as a chapter in Techniques ofVacuum Ultraviolet Physics, J~A-. Samson and D A. Ederer, eds.-, ·..-:~-:.:-':.::;:::;;;;r,;-:·.::~:~~:.::~-~~'*-~~,~~~;.=;t,ffl;.H;~:;;$,'~.~:~~::;;.:~< :.:,:::·.;:~·:..~.,·,;;;~.· l.t..•.-J.' "'"-""···,:·.:·· \ '-· . _ .....::' .~..... .:"~·~-!r.r;.e,.,...;. 17"'JC.(.; .• ,'~..: .••, ..._i;.·;~~(.:j. ... ..,.~1\;i:;.~ ...... J:' Academic Press, ....... ·.. ·... :.: ·..... ~ · ··: ·... · . .. .. .. - • 0 • ···...::; •• 0 ·.. • •• • •• ••• , •• •• •• ••• •••••• , 0 •• 0 .............. -·- " DISCLAIMER. This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain cmTect information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legahesponsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the -
Radio Astronomy & Radio Telescopes
Radio Astronomy & Radio Telescopes Tasso Tzioumis ([email protected]) Australia Telescope National Facility (ATNF) sms2020, Stellenbosch 2-6 March 2020 CSIRO ASTRONOMY AND SPACE SCIENCE Radio Astronomy – ITU definition 1.13 radio astronomy: Astronomy based on the reception of radio waves of cosmic origin. 1.5 radio waves or hertzian waves: Electromagnetic waves of frequencies arbitrarily lower than 3 000 GHz, propagated in space without artificial guide. • Astronomy covers the whole electromagnetic spectrum • Radio astronomy is the “low energy” part of the spectrum é 3 000 GHz Radioastronomy & Radio telescopes | Tasso Tzioumis Radio Astronomy “special” characteristics Technical challenges • Very faint signals – measured in 10-26 W/m2/Hz (-260 dBW) • “Power collected by all radiotelescopes since the start of radio astronomy would light a 1W bulb for less than 1 second” • à Need “sensitivity” i.e. large antennas and/or arrays of many antennas • à Very susceptible to intereference • Celestial structures at all scales: from very large to very small • à Need “spatial resolution” i.e. ability to see the details at all scales • à Need large antennas and/or arrays of many antennas • Astronomical events at all timescales(from < 1ms to > millions years) & and at all spectral resolutions (from < 1 Hz to GHz) • à Need very high time and frequency resolution • à Sensitive telescopes and arrays & extreme technical challenges Radioastronomy & Radio telescopes | Tasso Tzioumis Radio Astronomy “special” characteristics Scientific challenges • Radio -
Radio Astronomy
Theme 8: Beyond the Visible I: radio astronomy Until the turn of the 17th century, astronomical observations relied on the naked eye. For 250 years after this, although astronomical instrumentation made great strides, the radiation being detected was still essentially confined to visible light (Herschel discovered infrared radiation in 1800, and the advent of photography opened up the near ultraviolet, but these had little practical significance). This changed dramatically in the mid-20th century with the advent of radio astronomy. 8.1 Early work: Jansky and Reber The atmosphere is transparent to visible light, but opaque to many other wavelengths. The only other clear “window” of transparency lies in the radio region, between 1 mm and 30 m wavelength. One might expect that the astronomical community would deliberately plan to explore this region, but in fact radio astronomy was born almost accidentally, with little if any involvement of professional astronomers. Karl Jansky (1905−50) was a radio engineer at Bell Telephone. In 1932, while studying the cause of interference on the transatlantic radio-telephone link, he discovered that part of the interference had a periodicity of one sidereal day (23h 56m), and must therefore be coming from an extraterrestrial source. By considering the time at which the interference occurred, Jansky identified the source as the Milky Way. This interesting finding was completely ignored by professional astronomers, and was followed up only by the radio engineer and amateur astronomer Grote Reber (1911−2002). Reber built a modern-looking paraboloid antenna and constructed maps of the radio sky, which also failed to attract significant professional attention. -
The Methods and Experiments of Shape Measurement for Off-Axis
materials Article The Methods and Experiments of Shape Measurement for Off-Axis Conic Aspheric Surface Shijie Li 1,2,*, Jin Zhang 1,2, Weiguo Liu 1,2, Haifeng Liang 1,2, Yi Xie 3 and Xiaoqin Li 4 1 Shaanxi Province Key Laboratory of Thin Film Technology and Optical Test, Xi’an Technological University, Xi’an 710021, China; [email protected] (J.Z.); [email protected] (W.L.); hfl[email protected] (H.L.) 2 School of Optoelectronic Engineering, Xi’an Technological University, Xi’an 710021, China 3 Display Technology Department, Luoyang Institute of Electro-optical Equipment, AVIC, Luoyang 471009, China; [email protected] 4 Library of Xi’an Technological University, Xi’an Technological University, Xi’an 710021, China; [email protected] * Correspondence: [email protected] Received: 26 March 2020; Accepted: 27 April 2020; Published: 1 May 2020 Abstract: The off-axis conic aspheric surface is widely used as a component in modern optical systems. It is critical for this kind of surface to obtain the real accuracy of the shape during optical processing. As is widely known, the null test is an effective method to measure the shape accuracy with high precision. Therefore, three shape measurement methods of null test including auto-collimation, single computer-generated hologram (CGH), and hybrid compensation are presented in detail in this research. Although the various methods have their own advantages and disadvantages, all methods need a special auxiliary component to accomplish the measurement. In the paper, an off-axis paraboloid (OAP) was chosen to be measured using the three methods along with auxiliary components of their own and it was shown that the experimental results involved in peak-to-valley (PV), root-mean-square (RMS), and shape distribution from three methods were consistent. -
Optical Low-Coherence Interferometry for Selected Technical Applications
BULLETIN OF THE POLISH ACADEMY OF SCIENCES TECHNICAL SCIENCES Vol. 56, No. 2, 2008 Optical low-coherence interferometry for selected technical applications J. PLUCIŃSKI∗, R. HYPSZER, P. WIERZBA, M. STRĄKOWSKI, M. JĘDRZEJEWSKA-SZCZERSKA, M. MACIEJEWSKI, and B.B. KOSMOWSKI Faculty of Electronics, Telecommunications and Informatics, Gdańsk University of Technology, 11/12 Narutowicza St., 80-952 Gdańsk, Poland Abstract. Optical low-coherence interferometry is one of the most rapidly advancing measurement techniques. This technique is capable of performing non-contact and non-destructive measurement and can be used not only to measure several quantities, such as temperature, pressure, refractive index, but also for investigation of inner structure of a broad range of technical materials. We present theoretical description of low-coherence interferometry and discuss its unique properties. We describe an OCT system developed in our Department for investigation of the structure of technical materials. In order to provide a better insight into the structure of investigated objects, our system was enhanced to include polarization state analysis capability. Measurement results of highly scattering materials e.g. PLZT ceramics and polymer composites are presented. Moreover, we present measurement setups for temperature, displacement and refractive index measurement using low coherence interferometry. Finally, some advanced detection setups, providing unique benefits, such as noise reduction or extended measurement range, are discussed. Key words: low-coherence interferometry (LCI), optical coherence tomography (OCT), polarization-sensitive OCT (PS-OCT). 1. Introduction 2. Analysis of two-beam interference Low-coherence interferometry (LCI), also known as white- 2.1. Two-beam interference – time domain description. light interferometry (WLI), is an attractive measurement Let us consider interference of two beams emitted from method offering high measurement resolution, high sensi- a quasi-monochromatic light source located at a point P, i.e. -
Phase Tomography by X-Ray Talbot Interferometry
Phase Tomography by X-ray Talbot Interferometry X-ray phase imaging is attractive for the beamline of NewSUBARU, SPring-8. A SEM observation of weakly absorbing materials, such as (scanning electron microscope) image of the grating soft materials and biological tissues. In the past is shown in Fig. 1. The pitch and pattern height were decade, several techniques of X-ray phase imaging 8 µm and 30 µm, respectively. were reported and demonstrated [1]. Recently, we Through the quantitative measurement of the have developed an X-ray Talbot interferometer differential phase shift by the sample, extremely high- for novel X-ray phase imaging, including phase sensitive three-dimensional imaging, that is, X-ray tomography. This method is unique in that phase tomography, is attainable by X-ray Talbot transmission gratings are used to generate differential interferometry [3]. We demonstrated this with phase contrast (Fig. 1). Two gratings are aligned biological samples using monochromatic undulator along the optical axis with a specific distance X-rays at beamline BL20XU. Figure 2 shows a rabbit determined by the X-ray wavelength λ and the grating liver tissue with VX2 cancer observed by X-ray phase pitch d. The influence of refraction on the sample tomography using a CCD-based X-ray image detector placed in front of the first grating is observed just whose effective pixel size was 3.14 µm [4]. The behind the second grating. The detailed principle of cancerous lesion is depicted with a darker gray level the contrast generation is described in Refs. [2,3]. than the surrounding normal liver tissue. -
History of Radio Astronomy
History of Radio Astronomy Reading for High School Students Getsemary Báez Introduction form of radiation involved (soon known as electro- Radio Astronomy, a field that has strongly magnetic waves). Nevertheless, it was Oliver Heavi- evolved since the end of World War II, has become side who in conjunction with Willard Gibbs in 1884 one of the most important tools of astronomical ob- modified the equations and put them into modern servations. Radio astronomy has been responsible for vector notation. a great part of our understanding of the universe, its A few years later, Heinrich Hertz (1857- formation, composition, interactions, and even pre- 1894) demonstrated the existence of electromagnetic dictions about its future path. This article intends to waves by constructing a device that had the ability to inform the public about the history of radio astron- transmit and receive electromagnetic waves of about omy, its evolution, connection with solar studies, and 5m wavelength. This was actually the first radio the contribution the STEREO/WAVES instrument on wave transmitter, which is what we call today an LC the STEREO spacecraft will have on the study of oscillator. Just like Maxwell’s theory predicted, the this field. waves were polarized. The radiation emissions were detected using a 1mm thin circle of copper wire. Pre-history of Radio Waves Now that there is evidence of electromag- It is almost impossible to depict the most im- netic waves, the physicist Max Planck (1858-1947) portant facts in the history of radio astronomy with- was responsible for a breakthrough in physics that out presenting a sneak peak where everything later developed into the quantum theory, which sug- started, the development and understanding of the gests that energy had to be emitted or absorbed in electromagnetic spectrum. -
Resolution Limits of Extrinsic Fabry-Perot Interferometric Displacement Sensors Utilizing Wavelength Scanning Interrogation
Resolution limits of extrinsic Fabry-Perot interferometric displacement sensors utilizing wavelength scanning interrogation Nikolai Ushakov,1 * Leonid Liokumovich,1 1 Department of Radiophysics, St. Petersburg State Polytechnical University, Polytechnicheskaya, 29, 195251, St. Petersburg, Russia *Corresponding author: [email protected] The factors limiting the resolution of displacement sensor based on extrinsic Fabry-Perot interferometer were studied. An analytical model giving the dependency of EFPI resolution on the parameters of an optical setup and a sensor interrogator was developed. The proposed model enables one to either estimate the limit of possible resolution achievable with a given setup, or to derive the requirements for optical elements and/or a sensor interrogator necessary for attaining the desired sensor resolution. An experiment supporting the analytical derivations was performed, demonstrating a large dynamic measurement range (with cavity length from tens microns to 5 mm), a high baseline resolution (from 14 pm) and a good agreement with the model. © 2014 Optical Society of America OCIS Codes: (060.2370) Fiber optics sensors, (120.3180) Interferometry, (120.2230) Fabry-Perot, (120.3940) Metrology. 1. Introduction description of their resolution limits is of a great interest. Considering the wavelength scanning interrogation, an analysis Fiber-optic sensors based on the fiber extrinsic Fabry-Perot of errors provoked by instabilities of the laser frequency tuning is interferometers (EFPI) [1] are drawing an increasing attention present in [18], still only slow and large instabilities are from a great amount of academic research groups and several considered. companies, which have already started commercial distribution In this Paper, a mathematical model considering the main of such devices. -
Increasing the Sensitivity of the Michelson Interferometer Through Multiple Reflection Woonghee Youn
Rose-Hulman Institute of Technology Rose-Hulman Scholar Graduate Theses - Physics and Optical Engineering Graduate Theses Summer 8-2015 Increasing the Sensitivity of the Michelson Interferometer through Multiple Reflection Woonghee Youn Follow this and additional works at: http://scholar.rose-hulman.edu/optics_grad_theses Part of the Engineering Commons, and the Optics Commons Recommended Citation Youn, Woonghee, "Increasing the Sensitivity of the Michelson Interferometer through Multiple Reflection" (2015). Graduate Theses - Physics and Optical Engineering. Paper 7. This Thesis is brought to you for free and open access by the Graduate Theses at Rose-Hulman Scholar. It has been accepted for inclusion in Graduate Theses - Physics and Optical Engineering by an authorized administrator of Rose-Hulman Scholar. For more information, please contact bernier@rose- hulman.edu. Increasing the Sensitivity of the Michelson Interferometer through Multiple Reflection A Thesis Submitted to the Faculty of Rose-Hulman Institute of Technology by Woonghee Youn In Partial Fulfillment of the Requirements for the Degree of Master of Science in Optical Engineering August 2015 © 2015 Woonghee Youn 2 ABSTRACT Youn, Woonghee M.S.O.E Rose-Hulman Institute of Technology August 2015 Increase a sensitivity of the Michelson interferometer through the multiple reflection Dr. Charles Joenathan Michelson interferometry has been one of the most famous and popular optical interference system for analyzing optical components and measuring optical metrology properties. Typical Michelson interferometer can measure object displacement with wavefront shapes to one half of the laser wavelength. As testing components and devices size reduce to micro and nano dimension, Michelson interferometer sensitivity is not suitable. The purpose of this study is to design and develop the Michelson interferometer using the concept of multiple reflections. -
Essential Radio Astronomy
February 2, 2016 Time: 09:25am chapter1.tex © Copyright, Princeton University Press. No part of this book may be distributed, posted, or reproduced in any form by digital or mechanical means without prior written permission of the publisher. 1 Introduction 1.1 AN INTRODUCTION TO RADIO ASTRONOMY 1.1.1 What Is Radio Astronomy? Radio astronomy is the study of natural radio emission from celestial sources. The range of radio frequencies or wavelengths is loosely defined by atmospheric opacity and by quantum noise in coherent amplifiers. Together they place the boundary be- tween radio and far-infrared astronomy at frequency ν ∼ 1 THz (1 THz ≡ 1012 Hz) or wavelength λ = c/ν ∼ 0.3 mm, where c ≈ 3 × 1010 cm s−1 is the vacuum speed of light. The Earth’s ionosphere sets a low-frequency limit to ground-based radio astronomy by reflecting extraterrestrial radio waves with frequencies below ν ∼ 10 MHz (λ ∼ 30 m), and the ionized interstellar medium of our own Galaxy absorbs extragalactic radio signals below ν ∼ 2 MHz. The radio band is very broad logarithmically: it spans the five decades between 10 MHz and 1 THz at the low-frequency end of the electromagnetic spectrum. Nearly everything emits radio waves at some level, via a wide variety of emission mechanisms. Few astronomical radio sources are obscured because radio waves can penetrate interstellar dust clouds and Compton-thick layers of neutral gas. Because only optical and radio observations can be made from the ground, pioneering radio astronomers had the first opportunity to explore a “parallel universe” containing unexpected new objects such as radio galaxies, quasars, and pulsars, plus very cold sources such as interstellar molecular clouds and the cosmic microwave background radiation from the big bang itself. -
Moiré Interferometry
Moiré Interferometry Wei-Chih Wang ME557 Department of Mechanical Engineering University of Washington W.Wang 1 Interference When two or more optical waves are present simultaneously in the same region of space, the total wave function is the sum of the individual wave functions W.Wang 2 Optical Interferometer Criteria for interferometer: (1) Mono Chromatic light source- narrow bandwidth (2) Coherent length: Most sources of light keep the same phase for only a few oscillations. After a few oscillations, the phase will skip randomly. The distance between these skips is called the coherence length. normally, coherent length for a regular 5mW HeNe laser is around few cm, 2 lc = λ /∆λ , (3) Collimate- Collimated light is unidirectional and originates from a single source optically located at an infinite distance so call plane wave (4) Polarization dependent W.Wang 3 Interference of two waves When two monochromatic waves of complex amplitudes U1(r) and U2(r) are superposed, the result is a monochromatic wave of the Same frequency and complex amplitude, U(r) = U1(r) + U2 (r) (1) 2 2 Let Intensity I1= |U1| and I2=| |U2| then the intensity of total waves is 2 2 2 2 * * I=|U| = |U1+U2| = |U1| +|U2| + U1 U2 + U1U2 (2) W.Wang 4 Basic Interference Equation 0.5 jφ1 0.5 jφ2 Let U1 = I1 e and U2 = I2 e Then 0.5 I= I1_+I2 + 2(I1 I2) COSφ(3) Where φ = φ2 −φ1 (phase difference between two wave) Ripple tank Interference pattern created by phase Difference φ W.Wang 5 Interferometers •Mach-Zehnder •Michelson •Sagnac Interferometer •Fabry-Perot Interferometer -
Wide-Band, Low-Frequency Pulse Profiles of 100 Radio Pulsars With
A&A 586, A92 (2016) Astronomy DOI: 10.1051/0004-6361/201425196 & c ESO 2016 Astrophysics Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR M. Pilia1,2, J. W. T. Hessels1,3,B.W.Stappers4, V. I. Kondratiev1,5,M.Kramer6,4, J. van Leeuwen1,3, P. Weltevrede4, A. G. Lyne4,K.Zagkouris7, T. E. Hassall8,A.V.Bilous9,R.P.Breton8,H.Falcke9,1, J.-M. Grießmeier10,11, E. Keane12,13, A. Karastergiou7 , M. Kuniyoshi14, A. Noutsos6, S. Osłowski15,6, M. Serylak16, C. Sobey1, S. ter Veen9, A. Alexov17, J. Anderson18, A. Asgekar1,19,I.M.Avruch20,21,M.E.Bell22,M.J.Bentum1,23,G.Bernardi24, L. Bîrzan25, A. Bonafede26, F. Breitling27,J.W.Broderick7,8, M. Brüggen26,B.Ciardi28,S.Corbel29,11,E.deGeus1,30, A. de Jong1,A.Deller1,S.Duscha1,J.Eislöffel31,R.A.Fallows1, R. Fender7, C. Ferrari32, W. Frieswijk1, M. A. Garrett1,25,A.W.Gunst1, J. P. Hamaker1, G. Heald1, A. Horneffer6, P. Jonker20, E. Juette33, G. Kuper1, P. Maat1, G. Mann27,S.Markoff3, R. McFadden1, D. McKay-Bukowski34,35, J. C. A. Miller-Jones36, A. Nelles9, H. Paas37, M. Pandey-Pommier38, M. Pietka7,R.Pizzo1,A.G.Polatidis1,W.Reich6, H. Röttgering25, A. Rowlinson22, D. Schwarz15,O.Smirnov39,40, M. Steinmetz27,A.Stewart7, J. D. Swinbank41,M.Tagger10,Y.Tang1, C. Tasse42, S. Thoudam9,M.C.Toribio1,A.J.vanderHorst3,R.Vermeulen1,C.Vocks27, R. J. van Weeren24, R. A. M. J. Wijers3, R. Wijnands3, S. J. Wijnholds1,O.Wucknitz6,andP.Zarka42 (Affiliations can be found after the references) Received 20 October 2014 / Accepted 18 September 2015 ABSTRACT Context.