Optical system design
This presentation is the property of its rightful owner.
Sponsored Links
1 / 45

Optical System Design PowerPoint PPT Presentation


  • 159 Views
  • Uploaded on
  • Presentation posted in: General

Optical System Design. N. Geis MPE. Telescope. Entrance Optics -- chopper -- calibration optics. Bolometer. Spectrometer. Field splitter. To Slicer. Bolometer Optics. Image Slicer. Grating Spectrometer. Dichroic. Anamorphic System. Dichroic. Bolometer Optics. Bolometer Optics.

Download Presentation

Optical System Design

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Optical system design

Optical System Design

N. Geis

MPE

Optical System Design


Pacs optical system overview

Telescope

Entrance Optics

-- chopper

-- calibration optics

Bolometer

Spectrometer

Field splitter

To Slicer

Bolometer Optics

Image Slicer

Grating Spectrometer

Dichroic

Anamorphic System

Dichroic

Bolometer Optics

Bolometer Optics

Filter

Filter Wheel

Filter

Filter Wheel

Red Bolometer Array

Blue Bolometer Array

Red Photoconductor Array

Blue Photoconductor Array

Pacs Optical System Overview

Optical System Design


Definition of image scale

Definition of Image Scale

Optical System Design


Optical design top optics

Optical Design – Top Optics

  • Optical design for astronomical optical path

  • Image inverter (3 flats) at the beginning to compensate for telescope image tilt

  • Chopper assembly on outer side of FPU (servicing)

  • Labyrinth configuration for baffling (see straylight analysis)

  • Chopper throw (on sky) reduced to 1 full array size to allow for larger FOV of bolometers with same entrance field-stop/mirror sizes as previous design.

Optical System Design


Optical design top optics1

Optical Design – Top Optics

  • Optical design for calibration sources

  • Acceptable image quality of pupil

    • Köhler-type illumination (pupil on source aperture + a field stop)

    • Source aperture is projected onto M2/Cold Stop

    • No physical match in source for “field” stop => excellent uniformity expected

  • Re-use of existing entrance optics mirrors in reverse

  • Excellent baffling situation

    • Sources are outside of Instrument Cold Stop

    • Initial calibration path & field stop outside of Instrument Cold Stop

Optical System Design


Uniformity of illumination by calibrators

Uniformity of Illumination by Calibrators

The two sources produce mirrored illumination distributions, as seen from the detectors

Maximum (unwanted) modulation of the calibration signal by non-uniformity is ~ 5%

Compatible with the goal of having relative signal changes of 10% when chopping.

E.g., one could set operating points such that the range of signal is 7.5–12.5% when chopping.

Optical System Design


Top optics astronomical

Telescope

TO Fold 1

TO Fold 2

TO Fold 3

TO Active 1

Lyot Stop

TO Active 2

TO Active 3

Pupil

Field

TO Fold 4

Chopper

TO Active 4

TO Active 5

Common Focus, Top Optics

Top OpticsAstronomical

Optical System Design


Top optics calibration

Telescope

C2 Active 3

C1 Active 3

Cal. Source 1

Cal. Source 2

TO Fold 1

C1 Active 1 (Lens)

C2 Active 1 (Lens)

TO Fold 2

C1 Active 2

C2 Active 2

TO Fold 3

TO Active 1

Calibrator 1

Calibrator 2

Lyot Stop

TO Active 2

TO Active 3

Pupil

Field

TO Fold 4

Chopper

TO Active 4

TO Active 5

Common Focus, Top Optics

Top OpticsCalibration

Optical System Design


Optical components after top optics

Common Focus

Top Optics

Spectrometer

S Collimator 1

S Collimator 1

B Active 1

S Fold 1

S Collimator 2

S Collimator 2

Dichroic Beamsplitter

S Active 1

Grating

S Active 2

S Fold 2

B Fold R1

B Fold B1

S Fold 3

Slicer

Optics

B Active R1

B Active B1

S Fold 4

B Active R2

B Active B2

S Active 3

Filter

Filter Wheel

S Active 4

Red

Bolometer

Array

Blue

Bolometer

Array

Pupil

S Active 5

Field

S Active 6

Dichroic Beamsplitter

Filter

Filter Wheel

S Fold 5

Red

Spectrometer

Array

Blue

Spectrometer

Array

Optical componentsafter Top Optics

Photometer

Optical System Design


Optical design photometers

Optical Design – Photometers

  • Optical design for bolometer cameras finished

  • very good image quality

  • good geometry

  • excellent baffling situation

    • fully separate end trains

    • extra pupil and field stops possible on the way to detectors (use for alignment and baffling purposes)

    • exit pupil with filter at entrance window to cold (1.8K) detector housing

  • Bolometer arrays mounted close together on top of cryocooler

  • Photometers are a self-contained compact unit at FPU external wall

Optical System Design


Optical design spectrometers

Optical Design – Spectrometers

  • No Changes in optical design for spectrometer since IIDR

  • ILB column

  • Slicer output was reconfigured such that one pixel’s worth of space is intentionally left blank between slices at the slit focus and on the detector array

    • Reduces (diffraction-) cross-talk

    • helps with assembly of detector filters & alignmentgap of 0.75 mm between slit mirrorsgap of 3.6 mm between detector blocks for filter holder

  • Image quality diffraction limited

  • Excellent baffling situation

    • end optics for both spectrometers separated on “ground floor”

    • exit field stop of spectrometer inside a “periscope”

    • extra pupil and field stops possible in end optics (alignment, baffles)

Optical System Design


The image slicer

The Image Slicer

Optical System Design


Image slicer and grating in

Image Slicer and Grating (in)

Slit Mirror

Slicer Mirror

Capture Mirror

Grating

Optical System Design


Image slicer and grating in out

Image Slicer and Grating (in+out)

Slit Mirror

Periscope Optics

Capture Mirror

Slicer Stack

Grating

Optical System Design


Optical design summary

Optical Design Summary

  • Clean separation between optical paths – a result of the incorporation of the bolometers.

  • Realistic accommodation for mechanical mounts.

  • Significant savings in number of mirrors from the photoconductor-only design

  • Excellent image quality in both, photometers, and spectrometers

Optical System Design


Pacs envelope filled

PACS Envelope -filled

Optical System Design


Pacs optical functional groups

PACS Optical Functional Groups

Optical System Design


Optical system design

Photometer Optics

Filter Wheel I

Slicer

Optics

Blue Bolometer

0.3 K Cooler

Red Bolometer

Grating

Grating Drive

Encoder

sGeGaDetector

Red Spectrometer

Spectrometer

Optics

Chopper

Calibrator I and II

Calibrator Optics

sGeGa Detector

Blue Spectrometer

Filter Wheel II

Entrance Optics

Optical System Design


Optical system design

Entrance Optics & Photometer

Chopper

Lyot Stop

Telescope Focus

Dichroic

Calibrator I+II

FilterWheel

Blue

Bolometer

Cryocooler

Red

Bolometer

Optical System Design


Optical system design

Chopping Left

Optical System Design


Optical system design

Chopping Right

Optical System Design


Optical system design

The Spectrometer Section

Optical System Design


Pacs filter scheme

PACS Filter Scheme

Optical System Design


Filter rejection requirements determined from template observation scenarios

Filter Rejection Requirements(determined from template observation scenarios)

  • The requirements from 3 demanding astronomical scenarios...

  • planet with high albedo

  • deep imaging (Galactic/extragalactic)

  • FIR excess around bright star

  • ...lead to the required filter suppression factors.

  • Solid red line: total required suppression

  • Dashed blue line: model detector responsivity

(bolometers

only)

Suppression factor

detector response

filter transmission

overall response

Dotted green line: resulting required filter suppression factor

Wavelength [µm]

Optical System Design


Pacs filters

PACS Filters

  • Filter Functions

    • definition of spectral bands

      • photometric bands

      • order sorting for spectrometer grating

    • in-band transmission (high)

    • out-of-band suppression (thermal background, straylight, astronomical)

  • Filter implementation

    • Filter types (low-pass, high-pass, band-pass, dichroic)

    • Technology: Metal mesh filters developed at QMW

      • Proven technology

      • Robust

      • Excellent Performance

    • Filter location in optical path chosen for

      • rejection of thermal radiation from satellite

      • instrument stray light management

Optical System Design


Pacs filtering scheme

PACS Filtering Scheme

Optical System Design


Example prototype of long pass edge filter

Examples of QMW filters

Example: Prototype of Long Pass Edge filter

Examples of QMW filters

Optical System Design


Example filter chain long wavelength photometer

Example Filter Chain: Long-Wavelength Photometer

Dichroic beam splitter130.µm

Long-pass edge filters

52.µm

110.µm

125.µm

Short-pass edge filter 210.µm

Optical System Design


Filter summary

Filter Summary

  • Filter scheme with 4 or 5 filters in series in each instrument channel provides sufficient out-of-band suppression

  • Measured/expected in-band transmission

    • > 80 % for long-pass and dichroic filters

    • ~ 80 % for band-pass filters

    • > 40 % for filter combination

    • ~ 50 % expected

  • Requirements will be met

Optical System Design


Geometrical optics performance

Geometrical Optics Performance

Optical System Design


Optical system design

Optical Performance - Blue Bolometer

Optical System Design


Optical system design

Optical Performance - Geometry Blue Bolometer

3

2

1

Optical System Design


Optical system design

Optical Performance - Red Bolometer

Optical System Design


Optical system design

Optical Performance - Geometry Red Bolometer

Optical System Design


Optical system design

Optical Performance - Spectrometer

Center of Array, center l

Corner of Array, extreme l

Optical System Design


Optical system design

Optical Performance - Geometry Spectrometer

174.6 µm

175.0µm

175.4µm

75% Strehl @ 80 µm

90% Strehl @ 80 µm

“ILB”

Optical System Design


Optical system design

New Req?

New Goal?

PACS Optical Performance in a System Context

Optical System Design


Diffraction

Diffraction

Optical System Design


Illumination of lyot stop

2 Strategiesdepending on outcome of system straylight analysis

  • M2 as system stop (baseline):oversize cold stop by ~ 10% area (if only cold sky visible beyond M2, and straylight analysis allows)

  • Lyot stop as system stop (optional):undersize cold stop by ~ 10% area — throughput loss(if diffracted emission/reflection from M2 spider, M2 edge, or straylight is problematic)

Intensity (arb. units)

Radius [cm]

Illumination of Lyot Stop

  • M2 is system aperture

  • Image quality of M2 on Lyot stop determined by diffraction from PACS entrance field stop

  • Diffraction ring ~10% of aperture area

  • Cannot block “Narcissus effects” from M2 center at Lyot stop without throughput loss

GLAD 4.5

diffraction analysis

l=175 µm

Optical System Design


Diffraction analysis slicer spectrometer

Diffraction Analysis - Slicer/Spectrometer

  • Diffraction Analysis of the Spectrometer repeated with final mirror dimensions and focal lengths, and for a larger range of wavelengths.

  • The results were used

  • as inputs to a detailed grating size specification

  • for optimizing mirror sizes in the spectrometer path

=> Diffraction on the image slicer leads to considerable deviations from the geometrical footprint on the grating at all wavelengths

Optical System Design


Diffraction gallery at 175 m

Diffraction Gallery at 175 µm

telescope focus, re-imaged

“slice” through point spread function

entrance slit field mirror

capture mirror

Detector

array

pixel

grating

Optical System Design


Optical system design

Grating: The worst offenderat long wavelength

  • Considerable difference from geometrical optics footprint.

  • No noticeable spillover problem at short wavelength

  • Non-uniform illumination profile will lead to change in effective grating resolution => calculate/measure

Optical System Design


Optical system design

Grating: The worst offenderat long wavelength

  • Major difference from geometrical optics footprint.

  • Spillover of ~ 20% energy past grating & collimators at longest wavelength

  • Non-uniform illumination profile will lead to change in effective grating resolution => calculate/measure

Optical System Design


Diffractive walk off

Diffractive Walk-Off

  • Off-axis pixel diffraction throughput

    • For edge pixels, and long wavelength, asymmetric diffraction losses move the PSF peak ~ 0.3 pixel (3’’) from its expected spatial position.

    • Image scale on the sky for the spectrometer depends on wavelength  Effect needs to be fully characterized for astrometry/mapping.

Optical System Design


Optical system design

Diffraction Summary

  • System stop should be M2 - oversize PACS cold stop accordingly

  • Diffraction lobes introduced by slicer mirrors can still be transferred through most of the spectrometer optics (i.e., image quality is intact)

  • Considerable clipping occurs on collimator mirrors and grating at long wavelength

  • Losses due to “spill-over”:

    • up to 20% (205 µm), 15% (175 µm) other wavelengths tbd.

    •  80% “diffraction transmission” to detector for central pixel

  • Diffraction induced “chromatic aberration” needs further study

Optical System Design


  • Login