Transcript Slide 1

Using Nodal Aberration Theory to
Understand the Aberration Fields of
Multiple Unobscured TMA Telescopes
Kevin P. Thompson/ORA
Tobias Schmid/CREOL
Kyle Fuerschbach/UofR, Institute of Optics
Prof. Jannick P. Rolland/UofR Institute of Optics
2009 SPIE Annual Meeting
San Diego, CA
August 2, 2009
Motivation
• The James Webb Space Telescope (JWST) is a
Three Mirror Anastigmatic telescope (TMA),
corrected for the primary 3rd order
aberrations; spherical, coma, and astigmatism
• In one instrument path, NIRSPEC, there are
in-fact 3 additional unobscured TMAs in a row,
all with higher order aspheres – this may be a
first
• The motivation for this paper is to begin to
study the interaction of multiple TMA
telescopes from the perspective of nodal
aberration theory
Topics
• The JWST TMA form
• The TMAs in the JWST NIRSPEC instrument
• The evolution of the final aberration field for
a NIRSPEC-like configuration
• Plans for future study
The Hubble Space Telescope
and
The James Webb Space Telescope
JWST
HST
JWST
6.6m
HST
2.4m
Astronomical Telescopes
0.4 Deg. @ F/20
1890 - 1930
Cassegrain
1930 - 2000
Ritchey-Chretien
> 2000
JWST TMA
COMA
ASTIG.
JWST
A Field Bias, Obscured TMA
Tertiary
JWST
Segmented
Primary
Secondary
Tertiary
Field Bias used
to implement TMA
The JWST Telescope is
limited by 5th order AST
0.3
The offset field of view
for the instruments
of the JWST
ASTIGMATIC
FIELD CURVES
0.2
ANGLE(deg)
Y Field Angle in Object Space - degrees
X
Y0.20
0.1
0.15
0.0
3rd order
is zero
0.10
-0.1
0.05
-0.2
-0.5
0.0
0.50
FOCUS (MILLIMETERS)
-0.3
-0.3
-0.2
-0.1
0.0
0.1
X Field Angle in Object Space - degrees
0.2
0.3
Y Field Angle in Object Space - degrees
JWST Instrument Format
(SPIE 5437, 2004)
NIRSPEC Field
0.3
ASTIGMATIC
FIELD CURVES
ANGLE(deg)
X Y0.20
0.2
0.1
0.15
0.0
0.10
-0.1
0.05
-0.2
-0.5 0.0
0.50
FOCUS (MILLIMETERS)
-0.3
-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
X Field Angle in Object Space - degrees
NIRSPEC-like
Field ~ NIRCAM
Using 50% less Field of View allows developing a
design using only conics, which is less complex to
explain on a fundamental level
The Instrument is
rotated about 8 deg. from
the JWST axis about the
focal plane
JWST
Tertiary
Instrument
FSM
JWST
Focal
Plane
NIRSPEC Layout
Xavier Gnata PhD 2007
From JWST
Optical Design by J. Kohler
EADS Astrium(?)
See SPIE 5962, 2005
JWST
Axis
An All-Conic
NIRSPEC-like Example
NIRSPEC
Conic+C,D,E,?
NIRSPEC-Like
All-Conic
The Principle of
Multiple TMA Design
• TMA designs are rotationally symmetric
systems that use a combination of
– Field Bias
– Offset (Eccentric) Aperture
• Field Bias does not affect the aberration
field, only the part of it that is used
• Aperture Offset is used to move the
correction zone for the 3rd order aberrations
to the offset field point
TMA Characteristics
• Here
– JWST:
Field Bias 7.2 arc-minutes
• Instrument
Axis rotated 8 deg. about
JWST focal plane (3 TMAs)
– Relay:
Axis Offset ~ 425 mm
– Collimator:
Field Bias 17.5 degrees
Axis Offset 135 mm
– Camera:
Field Bias 17.5 degrees
Axis rotated 4.2 deg.
Aperture decentered 140mm
NIRSPEC
INSTRUMENT TMAs
NIRSPEC
INSTRUMENT TMAs
NIRSPEC
INSTRUMENT TMAs
Relay
Field Bias Only
NIRSPEC
Image Area
JWST
Axis
Collimator
Field Bias Only
17.5 Deg.
Field Bias
System
Optical Axis
Camera Axis
Of Symmetry
Intermediate
Image from
Relay
Camera
Field Bias and Offset
Aperture
System
Focal
Plane
Camera Axis
Of Symmetry
System
Optical Axis
17.5 Deg. Field Bias
Aperture
Decenter
140mm
0.67X Relay
180mm FOV @F/15
RMS
WFE
JWST
Focal
Plane
Astig.
Coma
8 deg.
Aperture
stop
Astig.
Coma
Published Predicted
Nominal Design
Performance - 2005
RMS WFE
vs.
Field
Optical Design of the Near-infrared Spectrograph NIRSpec
Jess Köhler, Markus Melf, Winfried Posselt, Wolfgang Holota, Maurice te Plate
EADS Astrium GmbH, P.O. 88090, Immenstaad, Germany
EADS Astrium GmbH, P.O. 81663, Ottobrunn, Germany
European Space Agency, Keplerlaan 1, PO Box 299, 2200 AG, Noordwijk, The Netherlands
Optical Design & Engineering II, edited by Laurent Mazuray, Rolf Wartmann
Proc. of SPIE Vol. 5962, (2005)
Collimator
17.5 Deg. @F/12.5
RMS
WFE
Astig.
Coma
17.5 Deg.
RMS
WFE
Astig.
Coma
Camera
17.5 deg. @ F/5.6
w/o
Offset
Stop
FINAL
CORRECTION
Offset
Stop
The Final Nominal System
Performance w/Four TMAs
Well-Corrected
JWST
Tertiary
JWST RMS WFE
At 200mm Off-axis
coma
astigmatism
Final
Focal
Plane
NIRSPEC-Like
Instrument Model
CONCLUSIONS
• The NIRSPEC Instrument on the JWST represents one
of the most complex mirror systems ever attempted
• Initial independent work with a system with a similar
geometry and all conics has indicated new aberration
field behavior, not observed previously, particularly
as it relates to higher order terms, like trefoil
(elliptical coma) – it appears the higher order
aberrations are moving to follow the lower order
• Nodal Aberration Theory (NAT) and Full Field
Displays (FFD) provide a unique, independent
method to understand and analyze the performance
of these groups of TMAs that can be extrapolated to
developing insight into what is needed to verify
alignment
• While this model is based on conics, the actual
design use higher order aspheres and operates
50% farther off-axis than this example