detailed optical design

Detailed Optical Design

6/27/2011 DL-NIRSP PDR, Tucson, AZ, June 23-24, 2011 76

Zemax Modeling of the Instrument

• An end-to-end (M1 to DL-NIRSP Focus) zemax model actually DOES NOT properly model the optical performance of the instrument

– Spectrograph slit performs a spatial filtering of the image in the spectral direction

– Slit diffraction cannot be properly modeled by zemax.

• Zemax does not allow for anisotropic Gaussian apodization

• Best Practice (using Zemax)…

→Model the feed optics and spectrograph separately

→Using Gaussian apodization to approximate the beam profile in the spectral direction

→Restrict the beam width in the spatial direction to the geometrical beam width

Feed Optics


Design Requirements for Feed Optics

DRD Description Requirements Comp

4.1.3 Feed Optics

4.1.3.

1

Feed Optics Construction All Reflecting Optics

4.1.3.

2

Resolution & FOV Coverage Dual Resolution/FOV

4.1.3.

3

Feed Optics Feature High-Resolution F/63 Mode

4.1.3.

4

F/63 Mode Resolution Diffraction-limited at 900 nm

4.1.3.

5

Feed Optics Feature Large-FOV F/24 Mode

4.1.3.

6

F/24 Mode Resolution Diffraction-limited at 2500 nm

4.1.3.

7

Feed Optics Feature Flexible Feed Optics Focal Plane

Location

6/27/2011 79 DL-NIRSP PDR, Tucson, AZ, June 23-24, 2011

Dual-Resolution/FOV Feed Optics – May, 2008

• OAP 1 re-images telescope pupil (AO mirror) to OAP2

• OAP 2 re-collimates the beam

• OAP 3 forms a F/24 image on the slit

• Fold mirrors 2 & 3 re-route the beam through a long focal length

mirror to forma F/93 focus on the slit

Dual-Resolution Feed Optics

April 2011 – Toleranced Version

Slitjaw & Context Imager

M10 – AO DM

OAP2

F/24 OAP3

OAP1 Fold Mirror, FM1

Fold Mirror, FM2 Fold Mirror, FM3

F/63 Spherical Mirror

• OAC 1,2, & 3

– fl =4,800 mm

– = 400 mm

– OAD = 750 mm

• Spherical Mirror

– fl = 12,400 mm

– = 400 mm

• Field Scanning Mirror

– OAC2

• Add 6 deg tilt to the focal plane to feed Context Imager

– Reduce the tilt of the spectrograph focal plane also…

Feed Optics & Context Imager – Current Design

• Relocate F/63 mirror to resolve interference with other instruments

• Add one more fold mirror before the spectrograph to resolve mechanical interference between the field scanning mirror and the grating

• Use Off-Axis Conic located at the pupil plane for field scanning

Feed Optics – DRD Flowdown

• All Reflecting Optics [DRD 4.1.3.1] • Dual Resolution/FOV [DRD 4.1.3.2] • High-Res. F/63 Mode [DRD 4.1.3.3] • F/63 Mode Diffraction-Limited @ 900

nm • Large FOV F/24 Mode [DRD 4.1.3.5] • F/24 Mode Diffraction-Limited @

2500 nm • Flexible Focus Location [DRD 4.1.3.7]

DL-NIRSP in Coudé Room

• Last exit on Autobahn…


Feed Optics Specifications

• DLF-FM1 – 6: Fold mirrors

– Flat mirror

• DLF-OAM1: Off-Axis Conic

– FL=4,800 mm

– = 400 mm

– OAD = 750 mm

– Conic = -0.838

• DLF-OAM2: Off-Axis Conic

– FL=4,800 mm

– = 225 mm

– OAD = 750 mm

– Conic = -1.193

• DLF-MF24: Off-Axis Conic

– FL=4,800 mm

– = 325 mm

– OAD = 1,000 mm

– Conic = -0.973

F/24

Feed Optics Optical Performance

H4RG upgrade ready

• F/63 Mode Diffraction-Limited @ 900 nm

• F/24 Mode Diffraction-Limited @ 2500 nm

F/63

Design Requirements for Feed Optics

DRD Description Requirements Comp

4.1.3 Feed Optics

4.1.3.

1

Feed Optics Construction All Reflecting Optics Y

4.1.3.

2

Resolution & FOV Coverage Dual Resolution/FOV Y

4.1.3.

3

Feed Optics Feature High-Resolution F/63 Mode Y

4.1.3.

4

F/63 Mode Resolution Diffraction-limited at 900 nm Y

4.1.3.

5

Feed Optics Feature Large-FOV F/24 Mode Y

4.1.3.

6

F/24 Mode Resolution Diffraction-limited at 2500 nm Y

4.1.3.

7

Feed Optics Feature Flexible Feed Optics Focal Plane

Location

Y


Context Imager


Design Requirements for Context Imager

DRD Description Requirement Comp

4.1.5 Context Imager

4.1.5.1 Context Imager

Construction

All Reflecting Optics

4.1.5.2 Context Imager Filter

Wheel No. of Position

5

4.1.5.3 Context Imager Camera

Wavelength Coverage

500 nm to 2500 nm


Pixel Format

Diffraction-limited spatial sampling

resolution with 1/2 science FOV coverage


Context Imager Optical Design


• All Reflecting Optics

– Offner Imager with Spherical Mirrors

Context Imager – DRD Flowdown


• All Reflecting Optics [DRD 4.1.5.1]

• No. of Wavelength: 5 [DRD 4.1.5.2]

Context Imager Mechanical Design


• All Reflecting Optics [DRD 4.1.5.1]

• No. of Wavelength: 5 [DRD 4.1.5.2]

Context Imager Wavelengths

λc [nm] λ [nm] Tmin [%] Φ [mm]

DLCI-BF1 500 5 40 50

DLCI-BF2 800 8 40 50

DLCI-BF3 1,100 11 40 50

DLCI-BF4 1,600 16 40 50

DLCI-BF5 2,200 22 40 50


F/24

Context Imager Optical Performance

F/63

• Diffraction-limited spatial sampling resolution with 1/2 science FOV coverage [DRD 4.1.5.4]

Design Requirements for Context Imager


4.1.5 Context Imager

4.1.5.1 Context Imager

Construction

All Reflecting Optics Y

4.1.5.2 Context Imager Filter

Wheel No. of Position

5 Y


Wavelength Coverage

500 nm to 2500 nm Y


Pixel Format

Diffraction-limited spatial sampling

resolution with 1/2 science FOV coverage

*


* Camera will be provided by the project

Spectrograph

Design Requirements for Spectrograph


4.1.7 Spectrograph

4.1.7.1 Spectrograph Construction All-Reflection Optics

4.1.7.2 Spectrograph Feature Flexible Entrance Slit Location

4.1.7.3 Multiple-Slit Capability ≥ 8 slits

4.1.7.4 Spectrograph Feature Motorized 4-Position Slit

Mask Wheel

4.1.7.5 Spectrograph Feature Motorized 3-Position Grating

Turret

4.1.7.6 Spectrograph Feature Dichroic Beamsplitter System

4.1.7.7 Spectrograph Feature Relay Optics System


Spectrograph Characteristics

• Reflecting Littrow

– 500 nm – 2500 nm wavelength coverage

– Off-Axis Conic Collimator/Camera Mirror, FL=1500 mm

• Using slit diffraction to fill the grating

– Default 36 um slit width

• Coarsely-ruled echelle grating

– Dispersion of grating beta angles for the spectral lines are roughly the

same (increase with wavelength), allowing for simultaneous multiple

spectral line observation

• 3-Grating turret for gratings with different blaze

– 7.9 line/mm, 26.7 deg blaze, R ~ 80,000 sampling

– 15.6 line/mm, 53 deg blaze, R ~ 200,000 sampling

– 23.2 line/mm, 63 deg blaze, R ~ 300,000 sampling

• Dichroic Beam Splitters

Simulation of

36-μm Slit

Diffraction

Spectral Resolution R = 50,000 – 200,000 [ISRD-2]

• Solid Line:

– No Slit

Diffraction

• Dashed Line:

– Slit Diffraction


H4RG

F/63, 30 um slit F/63, 24 um slit

F/63, 36 um slit F/24, 36 um slit

H2RG

Spectrograph Performance

Fx/12, Fy/24

*Airy disk size is a factor of 2 smaller than actual size…

Coarsely-Ruled Gratings

• Wavelength Range 500 nm – 2500 nm [ISRD-1]

⇒ All-Reflecting Spectrograph [DRD 4.1.7.1]

⇒Off-Axis Reflecting Littrow Spectrograph

The image quality of off-axis reflecting Littrow degrades very quickly as the location of the exit slit moves away from the position that is symmetric to the entrance slit around the chief ray of the on-axis focal point of the parent parabola.

• Simultaneous 4 wavelengths [ISRD-10] + Reflecting Littrow

⇒ Coarsely-Ruled Grating

Given a fixe grating α, the exit slits of all the wavelengths emerge within a small range in grating β, making it possible to maintain good image quality for all the wavelengths.

⇒ Dichroic Beam Splitters [DRD 4.1.7.6]


Spectrograph Optical Design

Dec. 2010

Context Imager

Spectrograph

Feed Optics Field Scanning Mirror

Spectrograph Optical Design

Current Version

• Add one fold mirror - Remove interference

between grating turret , slit mask, and field scanning mirror

• Reduce OAD (400 mm – 300 mm) of the off-axis conic mirror - Improved image quality - Eliminate cylindrical lenses in

the relay arms

Slit Mask

Grating

Off-Axis Conic, Collimator, Camera Mirror

Fold Mirror

Dichoric Beamsplitters

Air-spaced Doublet Relay Collimator

Wollaston DWDM Filter

Liquid Crystal x 2 (not shown)

Final Focus, FPA Int. Focus Spectral Field Mask

Air-spaced Doublet Relay Camera Lens

4.1.7.5 3-Position Grating Turret

• [ISRD-2] Spectral resolving power from 50,000 to 200,000

– In order to meet the large spectral resolution requirements (from

R ~ 50,000 to 200,000), the spectrograph will be equipped with a

3-slot grating turret to accommodate gratings with different blaze

angle.

• Grating Blaze and Resolution (assuming 1,500 mm focal length)

R [sampling resolution]

Groove Density [line/mm]

Blaze Angle [deg]

~ 300,000 TBD 63

~ 200,000 TBD 53

~ 80,000 TBD 26.7

~ 50,000 TBD 6.18


4.1.7.5 3-Position Grating Turret

• [ISRD-2] Spectral resolving power from 50,000 to 200,000

– In order to meet the large spectral resolution requirements (from

R ~ 50,000 to 200,000), the spectrograph will be equipped with a

3-slot grating turret to accommodate gratings with different blaze

angle.

• Default Grating List (with 1,500 mm focal length)

R [sampling resolution]

Groove Density [line/mm]

Blaze Angle [deg]

Availability

~ 300,000 23.2 63 Off-the-Shelf

~ 200,000 15.6 53 Custom

~ 80,000 7.9 26.7 Off-the-Shelf

~ 50,000 31.7 6.18 Off-the-Shelf


Grating Efficiency

• Coarsely-Ruled echelle gratings operate at high order for the

spectral lines within the working range of the spectrograph.

• Small variation of grating βs for a fixed grating α for the spectral

lines

⇒ High diffraction efficiency for most of the lines…


Why R = 200,000 with Custom 15.6 line/mm,

53 deg blaze grating?

• Increased number of slits

– Better system efficiency

• Relaxed DWDM filter specification

– broader bandpass

– Lower filter cost

– An important design goal of DL-NIRSP is to achieve high system

efficiency to improve the temporal resolution of the observation,

which is critical for the study of the dynamic of solar magnetism.


Relay Optics

• 1:1 relay with fl=400 mm air-spaced doublet

• Spectral Field Masks at spectrograph focus

– Relaxed DWDM filter bandwidth specification

• Intermediate pupil plane available for

– DWDM Bandpass Isolation Filter

– Polarization Modulators (Liquid Crystal Variable Retarders)

– Wollaston Polarizing Beamsplitter

– Reduce size requirement for optics

Dual-Beam Polarimetry

Spectrograph Focus

With Spectral Mask

Final Focus With Wollaston Beamsplitter



4.1.7 Spectrograph

4.1.7.1 Spectrograph Construction All-Reflection Optics Y

4.1.7.2 Spectrograph Feature Flexible Entrance Slit Location

4.1.7.3 Multiple-Slit Capability ≥ 8 slits ?


Mask Wheel


Turret

4.1.7.6 Spectrograph Feature Dichroic Beamsplitter System Y

4.1.7.7 Spectrograph Feature Relay Optics System Y


Motorized Slit Mask Wheel and Grating Turret


Flexible Entrance Slit Location

Scanning Long-Slit Spectrograph Mode


Flexible Entrance Slit Location

Fiber-Optic IFU Mode




4.1.7 Spectrograph

4.1.7.1 Spectrograph Construction All-Reflection Optics Y

4.1.7.2 Spectrograph Feature Flexible Entrance Slit Location Y

4.1.7.3 Multiple-Slit Capability ≥ 8 slits ?


Mask Wheel

Y


Turret

Y

4.1.7.6 Spectrograph Feature Dichroic Beamsplitter System Y

4.1.7.7 Spectrograph Feature Relay Optics System Y


Fiber-Optic IFU

for Coronal Magnetometry


Design Challenges of Coronal Magnetometry

• One of the promises of the 4-m aperture of the ATST is to deliver

high photon flux required by coronal magnetometry

• From 0.4-m Evans Coronagraph to 4-m ATST is real nice, but…

– Focal Plane Array pixel size does not increase by 10x…

– Focal plane array chip size does not increase by 10X…

– Grating size does not increase by 10X…

– F/# of optics wants to stay the same…

⇒ It is very difficult to do low spatial resolution, large FOV

observation with large telescope!


Fiber-Optic IFU for Coronal Magnetometry

• Optical fiber can be used to create large pixel detector array…

• Maintain a compact form factor at the exit end so that current small

grating and spectrograph can still be used…


Microlens Array

Optical Fibers

From Telescope

Telescope Focal Plane

Design Requirements for Fiber-Optic IFU


4.1.6 Fiber-Optic IFU

4.1.6.1 Fiber-Optic IFU Spatial

Sampling Resolution

1 arcsec

4.1.6.2 Fiber-Optic IFU FOV Coverage 1 arcmin

4.1.6.3 Telescope-to-Fiber Coupling Microlens Array Coupled IFU

4.1.6.4 Fiber-Optic IFU Feature Multiple-Slit Exit Array


Fiber-Optic IFU Design Requirements Flowdown

• [DRD 4.1.6.1] Fiber-Optic IFU Spatial Sampling Resolution 1”

– 0.500 mm pitch for F/24 feed

• [DRD 4.1.6.2] Fiber-Optic IFU Spatial Field of View Coverage 1 arcmin

– 64 x 64 Input Array

• [DRD 4.1.6.3] Microlens Array Coupled IFU

– Duh…

• [DRD 4.1.6.4] Multiple-Slit Exit Array

– 16 x (1 x 256) exit array

– 0.144 mm pitch


Coronal Fiber-Optic IFU with F/24 Feed


Design Requirements for Fiber-Optic IFU


4.1.6 Fiber-Optic IFU

4.1.6.1 Fiber-Optic IFU Spatial

Sampling Resolution

1 arcsec Y

4.1.6.2 Fiber-Optic IFU FOV Coverage 1 arcmin Y

4.1.6.3 Telescope-to-Fiber Coupling Microlens Array Coupled IFU Y

4.1.6.4 Fiber-Optic IFU Feature Multiple-Slit Exit Array Y


Polarimetry


Polarimetry

• Polarization measurements of all ATST instruments are strongly

coupled to the telescope polarization property…

– Close collaboration with ATST Project is needed to achieve the

polarization accuracy required for the science…


Polarimeter Design Requirements


4.1.8 Polarimeter

4.1.8.1 Polarimeter Feature In-Instrument, High-Speed

Wavelength-Specific Polarization

Modulation Units

4.1.8.2 Polarimeter Feature Broadband Polarization

Modulation Unit

4.1.8.3 Polarimeter Feature Polarization Calibration Optics

4.1.8.4 Polarization Accuracy 5 x 10-4

4.1.8.5 Polarization Feature Dual-beam Polarimetry Capable


Polarimeter Requirements Flowdown

• [DRD 4.1.8.1] In-Instrument, High-Speed Wavelength-Specific Polarization Modulation Units – Default Meadowlark SWIFT dual-LCVR Modulator for each relay arm

• [DRD 4.1.8.2] Broadband Polarization Modulation Unit

– Utilize facility GOS modulator for coronal IFU

• [DRD 4.1.8.3] Polarization Calibration Optics – Utilize facility GOS polarization calibration optics

• [DRD 4.1.8.4] Polarization Accuracy 5 x 10-4

– Working with Project Instrument Scientist…

• [DRD 4.1.8.5] Dual-beam Polarimetry Capable – Designed-In for scanning long-slit mode – Need additional Wollaston beamsplitter before fiber-optic IFU – Decreased fiber-optic IFU FOV coverage (60” x 30”)


Fiber-Optic IFU Mosaic


Fiber-Optic IFU FOV Option

• Increase input fiber-optic IFU array pitch to 2 mm

– 4”/fiber spatial sampling

– 256” x 128” FOV in single beam

– 128” x 128” FOV in dual beam


Microlens Array

Optical Fibers

From Telescope

Telescope Focal Plane

Polarimeter Design Requirements Compliance


4.1.8 Polarimeter

4.1.8.1 Polarimeter Feature In-Instrument, High-Speed

Wavelength-Specific Polarization

Modulation Units

Y

4.1.8.2 Polarimeter Feature Broadband Polarization

Modulation Unit

Y

4.1.8.3 Polarimeter Feature Polarization Calibration Optics Y

4.1.8.4 Polarization Accuracy 5 x 10-4 Y*

4.1.8.5 Polarization Feature Dual-beam Polarimetry Capable Y


*Project activities…

detailed optical design

Documents