Interferometer Types

26 Pages·2004·0.97 MB·English

Introduction to Optics
part II
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
Interferometer Types (NASA, AirForce)
SIM-2006 Space Technology 3-2005 Air Force UltraLITE
Michelson Interferometer Michelson Interferometer Fizeau Interferometer
Precision Astrometry
Earth Observing Telescope
TPF - 2011
NGST - 2007
Michelson Interferometer A Common Secondary Mirror (MMT, Fizeau)
Primary Mirror = 8 m diameter
Chart: 2 16.684 Space Systems Product Development MIT Space Systems Laboratory
February 13, 2001
Interferometer Types (Ground)
Keck Interferometer-2006
Michelson Interferometer (Infrared)
Twin 10 m Keck Telescopes and four 1.8 m outriggers
Baseline 85m
Palomar Testbed Interferometer
Michelson Interferometer (Infrared)
Testbed for Keck and SIM
Mark III Interferometer
Michelson Interferometer (Visible)
Keck Observatory:
Multiple Mirror Telescope (MMT)
Fizeau Interferometer (Visible, Infrared)
36 hexagonal segments => 10 m overall aperture
Chart: 3 16.684 Space Systems Product Development MIT Space Systems Laboratory
February 13, 2001
Michelson Interferometer
Michelson Interferometer
Stellar Imaging with Michelson Interferometer
wa
vefr y v v v y
o
nt
+
x u u u x
FT -1
"FT "
Beamsplitter
Object u-v (Fourier plane) Reconstructed
Collector
image
Baseline orientations:
Detector
Collector
Optical delay
Detector line
Independent Light Collectors feed light to a common beam
combiner. Get interfered fringes => Inverse Fourier Transform
(CLEAN,MEM)
Suitable for Astronomical Objects:
Unchanged over a long period of time
Chart: 4 16.684 Space Systems Product Development MIT Space Systems Laboratory
February 13, 2001
Fizeau Interferometer
Fizeau Interferometer
Detector Detector
Telescopes
"Beam combiner"
Sparse aperture
Telescope Fizeau Interferometer
Telescope
1 2 3
Gives a direct image of a target from a large combined primary
mirror, and a wide field of view (Imaging applications in space
and MMT)
Suitable for Wide Angle Astrometry
And for rapidly changing targets (Terrestrial, Earth Objects)
Chart: 5 16.684 Space Systems Product Development MIT Space Systems Laboratory
February 13, 2001
Comparison (Fizeau, Michelson)
Fizea u Miche lson Inte rferomete r
Int erferomet er
Produce a direct im age o f its Takes a subset of u-v points
targ et (Full Instant u-v c overage obtaine d a period o f time.
provided)
Wide angle(f ield) of view Ast rome try,
imaging app lications Nulling Interferom etry
Rapidly Cha nging targe ts Targ et unchan ged
(Terre strial, Ea rth Objects) (Ast ron omical Objects)
Takes the comb ined sci ence Me asure s points in Fourier
light from all the apertures and tran sform of ima ges => Inverse
focuses it into C CD FFT needed
U-V resolution depends on both Angula r re solution de pend s
the separa tion and the size of solely on the separa tion of
aperture s aperture s
Optima l Configuration: The angul ar resolution im proves
Golay (m inim um aper ture size) as the separation increases
Chart: 6 16.684 Space Systems Product Development MIT Space Systems Laboratory
February 13, 2001
Common Secondary vs Sub Telescope
Common
Secondary Mirror
Array
Phased Sub-
Telescope Arrays
Beam
CCD
Combiner
Common Primary Sub Telescope Fizeau
Precise Off Axis Configuration Need Combiner + Phase sensing and
Off Axis Optical Aberration compensater mechanism (complex)
Less Central Obstruction(Off Axis) On Axis Suffers Central Obstruction
Hard to change the Configuration Can employ Off-the-shelf telescopes
AirForce is studying two options for UltraLITE(Golay 6)
Chart: 7 16.684 Space Systems Product Development MIT Space Systems Laboratory
February 13, 2001
Optical Arrays
Instead of using a single aperture use several
and combine their light to form a single image
Aperture positions (uv) are critical -
look at combined PSF / Transmissivity
of the Optical Array
Optical Array Configuration
0.25
0.2
0.15
0.1
m]
e [ 0.05
c
n
a 0
st
Di
-0.05
-
Y
Transmissivity Function: -0.1
-0.15
-0.2
Derivation see separate
-0.25
handout (Mennesson)
-0.3 -0.2 -0.1 0 0.1 0.2 0.3
X -Distance [m]
Chart: 8 16.684 Space Systems Product Development MIT Space Systems Laboratory
February 13, 2001
CDIO: Breaking the Paradigm
Optical Array Configuration
Optical Array Configuration
PPhhyyssiiccaall 0.4
0.3
AAppeerrttuurree 0.3
0.2
LLaayyoouutt 0.2
m] 0.1 m] 0.1
e [ e [
Distanc 0 Distanc 0
Y - -0.1 Y - -0.1

-0.2 Compare -0.2
-0.3 Architectures -0.3
with -0.4
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
X - Distance [m] Quantitative -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5
X - Distance [m]
GGoollaayy--33 00..66 mm tteelleessccooppee
MMoonnoolliitthhiicc 00..66 mm tteelleessccooppee
Metrics
PPSSFF
Chart: 9 16.684 Space Systems Product Development MIT Space Systems Laboratory
February 13, 2001
Effective Radius of Optical Array
How to find the effective
radius(Reff) of the array?
R
• =the radius of the array
eff
thought as that of a monolithic
aperture.
• UV coverage plot
x − x y − y
u = ± 2 1 v = ± 2 1
λ λ
x,y is any point within aperture
R
• : the maximum radius of
uv
uv plot without any holes
• R = 0.5R
eff uv
• Fill Factor: the array’s total
collecting area over the area of a
filled aperture with the same uv
coverage(the same Reff)
Chart: 10 16.684 Space Systems Product Development MIT Space Systems Laboratory
February 13, 2001