麻省理工学院：《Satellite Engineering》Lecture 6 Introduction to Optics part I

Introduction to Optics part I Overview lecture Space Systems Engineering presented by: Prof. David Miller prepared by: Olivier de Weck Revised and augmented by Soon-Jo Chung Chart: 1 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

Introduction to Optics part I Overview Lecture Space Systems Engineering presented by: Prof. David Miller prepared by: Olivier de Weck Revised and augmented by: Soon-Jo Chung Chart: 1 16.684 Space Systems Product Development MIT Space Systems Laboratory February 13, 2001

Or utline Goal: Give necessary optics background to tackle a space mission, which includes an optical payload Light .Interaction of light w/environment o Optical design fundamentals Optical performance considerations .Telescope types and CCd design interferometer types Sparse aperture array Beam combining and control Chart: 2 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

Outline Goal: Give necessary optics background to tackle a space mission, which includes an optical payload •Light •Interaction of Light w/ environment •Optical design fundamentals •Optical performance considerations •Telescope types and CCD design •Interferometer types •Sparse aperture array •Beam combining and Control Chart: 2 16.684 Space Systems Product Development MIT Space Systems Laboratory February 13, 2001

Examples- Motivation Spaceborne Astronomy NGC 6543 HST WFPC2 Planetary nebulae NGc 6543 September 18, 1994 Hubble space telescope Chart: 3 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

Examples - Motivation Spaceborne Astronomy Planetary nebulae NGC 6543 September 18, 1994 Hubble Space Telescope Chart: 3 16.684 Space Systems Product Development MIT Space Systems Laboratory February 13, 2001

Properties of light Wave nature Duality Particle nature VE Energy of Q=hv Solution Photons are E-Ae(kr-ol+o)"packets of energy E Electric field vector H: Magnetic field vector Ponting vector: S=EXH 4兀 Spectral Bands (wavelength 2: Wavelength: n=v 2丌 Ultraviolet(UV)300 A-300 nm Visible light 400 nm-700 nm 2丌 Near IR(NIR)700 nm-2.5 um Wave Number:k Chart: 4 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

Properties of Light Wave Nature Particle Nature 2 2 HP w E Duality ’ E Energy of  2 0 a photon Q=hQ Detector c wt 2 Solution: Photons are ( i kr ZtI ) “packets of energy” E Ae E: Electric field vector H: Magnetic field vector Poynting Vector: S c E u H 4S Spectral Bands (wavelength O): Wavelength: O Q 2S QT Ultraviolet (UV) 300 Å -300 nm Z Visible Light 400 nm - 700 nm 2S Near IR (NIR) 700 nm - 2.5 Pm Wave Number: k O Chart: 4 16.684 Space Systems Product Development MIT Space Systems Laboratory February 13, 2001

Reflection - mirrors Mirrors (reflective devices)and Lenses refractive devices) are both"Aperturesand are similar to each other Law of reflection Mirror geometry given as a conic section rot surface z(p) k+1 k+1)P Reflected wave is also in the plane of incidence Specular Circle: k=0 Ellipse-1<k<0 Reflection Parabola: k=-1 Hyperbola: K<-1 SU mirror Detectors resolve Images produced by (solar)energy reflected from detector a target scene* in visual and nir rather than self-emissions Target Scene Chart: 5 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

Reflection-Mirrors Mirrors (Reflective Devices) and Lenses (Refractive Devices) are both “Apertures” and are similar to each other. Ti To Law of reflection: Ti=To Mirror Geometry given as a conic section rot surface: 1 2 z( )  U r  r  k 1 U  Reflected wave is also k 1 in the plane of incidence Circle: k=0 Ellipse -1<k<0 Specular Reflection Parabola: k=-1 Hyperbola: k<-1 Detectors resolve Images produced by (solar) energy reflected from a target scene* in Visual and NIR. *rather than self-emissions Target Scene sun mirror detector Chart: 5 16.684 Space Systems Product Development MIT Space Systems Laboratory February 13, 2001 2

Transmission-Refraction Medium 1 Medium 2 n Recall snell's law Incident ray n, sin b,=n sin e Refracted ray Light Intensity S Ar vetz C Dispersion if index of refraction is wavelength dependent n(n) Refractive devices not popular in space imaging since we need different lenses for uV. visual and ir Chart: 6 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

Transmission-Refraction Medium 1 Medium 2 n1 n 2 Recall Snell’s Law n1 sin T n 2 Incident ray 1 2 sin T Refracted Ray H E 2 Light Intensity S c 4S Dispersion if index of refraction is wavelength dependent n( O ) Refractive devices not popular in space imaging , since we need different lenses for UV, visual and IR. Chart: 6 16.684 Space Systems Product Development MIT Space Systems Laboratory February 13, 2001

Polarization Light can be represented as a transverse electromagnetic wave made up of mutually perpendicular t fluctuating electric and magnetic fields Ordinary white light is made up of waves that fluctuate at all possible angles. Light is considered to be linearly polarized"when it contains waves that only fluctuate in one specific plan( Polarizers are shown) In-phase=> 45 degrees linearly polarized 90 degree out of phase->circular Chart: 7 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

Polarization Light can be represented as a transverse electromagnetic wave made up of mutually perpendicular, fluctuating electric and magnetic fields. Ordinary white light is made up of waves that fluctuate at all possible angles. Light is considered to be "linearly polarized" when it contains waves that only fluctuate in one specific plan (Polarizers are shown) In-phase=> 45 degrees linearly polarized 90 degree out of phase->circular Chart: 7 16.684 Space Systems Product Development MIT Space Systems Laboratory February 13, 2001

Interference Interference: Interaction of two or more light waves yielding a resultant irradiance that deviates from the sum of the component irradiances If the high part of one wave (its crest)overlaps precisely with the high part 十〓 of another wave we get enhanced light Crest crest= strong light (-1)=2m/k=m If the high part of one wave overlaps precisely with the low part of another 十 wave(its trough), they cancel each other out Crest Trough= Darkness (-12)=mm/k=m Conditions of interference need not be in phase with each source but the initial phase difference remains constant coherent a stable fringe pattern must have nearly the same frequency. But, white light will produce less sharp, observable interference should not be orthogonally polarized to each other Chart: 8 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

QuickTime™ and a Cinepak decompressor are needed to see this picture. Interference Interference: Interaction of two or more light waves yielding a resultant irradiance that deviates from the sum of the component irradiances If the high part of one wave (its crest) overlaps precisely with the high part of another wave, we get enhanced light. (r1  r2 Crest + Crest = Strong Light ) 2Sm / k mO If the high part of one wave overlaps precisely with the low part of another wave (its trough), they cancel each other out. (r1  r2 ) Sm / k 1 Crest + Trough = Darkness mO 2 MIT Space Systems Laboratory (coherent) each other Conditions of Interference: • need not be in phase with each source, but the initial phase difference remains constant • A stable fringe pattern must have nearly the same frequency. But,white light will produce less sharp, observable interference • should not be orthogonally polarized to Chart: 8 16.684 Space Systems Product Development February 13, 2001

Diffraction Diffraction occurs at the edges of optical elements and field stops, this limits the Field-of-View(FOv) This is THE limiting factor, which causes spreading of screen J=IEl light and limits the"sharpness u of an image 入 pinhole u=-bsin e Incoming light B Intensity B-aperture sIze 0-angle of boresight pattern Fraunhofer diffraction Thoery (very distant object) is applied sine function is replaced by J, for a circular aperture Chart: 9 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

Diffraction Diffraction occurs at the edges of optical elements and field stops, this limits the Field-of-View (FOV). This is THE limiting factor, Intensity T 2 §sin u · which causes spreading of screen I E Io ¨ ¸ light and limits the “sharpness © u ¹ of an image” O pinhole S u BsinT O Incoming light B B - aperture size T - angle of boresight pattern Fraunhofer Diffraction Thoery (very distant object) is applied. sine function is replaced by J1 for a circular aperture Chart: 9 16.684 Space Systems Product Development MIT Space Systems Laboratory February 13, 2001 2

Derivation of angular resolution hnkensty Pattem(PSF) of Crcuar Apertur 2 =|E2 1: Bessel function of the first kind(order 1) =3.83=- Bine=-B6 383元12B aperture sIze rB b 0-angle of 383(1tN词 7.02(2ndN = Rayleigh criterion Angular Resolution(Resolving Power): the two star points (i.e, two Airy discs Goal is to design optical system to be diffraction limited at the wavelength of interest Chart: 10 February 13, 2001 16.684 Space Systems Product Development MIT Space Systems Laboratory

Derivation of Angular Resolution T I E 2 Io 2 J1( u ) u § ©¨ · ¹¸ 2 u 3.83 S O Bsin T S O B T T 3.83 O SB 1.22 O B telescope's ability to clearly separate, or resolve, two star points (i.e., two Airy discs) J ) B - aperture size - angle of boresight Angular Resolution(Resolving Power) :the => Rayleigh Criterion 1:Bessel function of the first kind(order 1 Goal is to design optical system to be diffraction limited at the wavelength of interest. Chart: 10 16.684 Space Systems Product Development MIT Space Systems Laboratory February 13, 2001