optical and infrared telescope fundamentals

Optical and Infrared

Telescope Fundamentals

Peter WizinowichDunlap Summer School – 26 July, 2018Ethan Tweedie Photography

Pre-Keck

2

Keck Staff

3

Telescope Design Considerations

• Science goals

– Type of science, science instruments

• Performance

– Image quality, angular resolution, field of view,

wavelength coverage, throughput, background,

observing efficiency

• Cost & Schedule

4

Performance

Image Quality Error Budget

5

Image Quality

Optics Environment Other

Optical Figure (M1, M2, M3)

Optical Alignment

Instrument Optics

Atmospheric Seeing

Dome Seeing

Wind Shake

Vibrations

Active Control System Noise

Scattered Light

Sky & Thermal Background

Maunakea

6

7

Dennis Crabtree, 2018

Some Optics Basics

Human Eye

9

Resolution & Sensitivity Gains

10θ ~ λ/r0 λ/D

Diffraction-limited Imaging

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0

0.2

0.4

0.6

0.8

1

0 0.05 0.1 0.15 0.2 0.25

Stre

hl R

atio

RMS Wavefront Error (waves)

Perfect Keck image

SR=0.62 SR=0.25

Optical Aberrations - Phase

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Optical Aberrations - Image

13

14

Optical Aberrations - Distortion

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Keck Telescope Optics

Telescope Error Budget

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1818

Telescope Alignment

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Scott Foundation 21

Glass Fabrication

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0

100

200

300

400

500

0 1 2 3 4 5

Sph

ere

, z (

mm

)

S (m)

-2.0

-1.5

-1.0

-0.5

0.0

0 1 2 3 4 5Pa

rab

ola

-S

ph

ere

, ∆z

(mm

)

S (m)

Primary Mirror Focus

23

Sphere z = 𝑟 − 𝑟2 − 𝑆2

r = 35 m for Keck

Material to be removed =

Parabola 𝑧 =𝑆2

2𝑟- Sphere

Sphere

z

S

r

f

Focal length f = r/2

Polishing

24

Optical Testing

25

Ion Figuring

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Primary Mirror Segment

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Segment Support

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Mirror Segment

Axial Insert

Axial Flex Rod

Inner or Outer Whiffletree Tripod

Secondary Whiffletree Beam

Primary Whiffletree Beam

Actuator

Radial Support Pad

Radial Pad Flexure

Radial Flex Ring

Diaphragm

Radial Post

Mirror Segment Subcell

Telescope Mirror Cell

Primary Mirror Segment

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30

Large

Monolithic

Mirrors

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Large

Monolithic

Mirrors

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33

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Shack Hartmann Wavefront Sensor

35

f

Telescope Alignment

• Segment tilts

• Secondary piston & tilt

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Segment Warping

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Segment Warping

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Segment Phasing

Science Instruments

40

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Dome Design

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43

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The Future

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Keck Opportunities• Akamai• AstroTech• Keck Visiting Scholars• Postdoc Positions

46

Questions?

Adaptive Optics at

Keck Observatory

K1: OSIRISK2: NIRC2

K2: NIRSPEC

ElevationRing

Enclosure withroof removed

AO Optics Bench

Rails to deck

NasmythPlatform

ElectronicsRacks

AO Enclosure

49

Light from Telescope

NIRC2

NIRSPEC

1 meter

Keck II AO Bench

Keck I AO Bench

50

OSIRIS

AO Bench

Keck II Laser(2016)

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Keck II Laser Launch Telescope

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Launch

Telescope

Keck AO Science

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Keck LGS

HST

Keck II Near-Infrared

Wavefront Sensing with

NIRC2 Vortex

& NIRSPEC Fiber Injection

Pyramid WFS & Fiber Injection

55

Optical FeedFi

ber

Ext

ract

ion

U

nit

(FE

U)

NIRC2 Vortex Coronagraph

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Pyramid & Fiber Injection Layout

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1 meter

FIU Plate

PWS Plate

FSM Assembly

Near-IR Pyramid Wavefront Sensor

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Near-IR Pyramid

Wavefront Sensor

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Ethan Tweedie Photography

Other Keck AO

Developments

Star = PSF PSF-R Difference

On-axis PSF Demo

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Point Spread Function

Reconstruction

Profiler

New Keck II Real-time Controller

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Keck All sky Precision AO (KAPA)

• Laser tomography

– TOPTICA laser

– Asterism generator

– New WFS camera

– New RTC

• Near-IR tip-tilt

– Multiple NGS

• PSF-R for OSIRIS

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Ethan Tweedie Photography

Thanks / Merci