K-D-PR-1100-009

Fabrication and testing of KGMT Fabrication and testing of KGMT FSM prototypeFSM prototype

Oct. 4. 2010

Ho-Soon Yang, Hak-Yong Kihm, Il-Kwon Moon, Jae-Bong Song, Yun-Woo Lee

Korea Research Institute of Standards and Science, Korea

Young-Soo KimKorea Astronomy & Space Science Institute, Korea

Contents

Objective of project Recent experiences in KRISS Manufacturing flow diagram Optical testing Working cell design Future works

2

Objective

3

Technology development related to manufacturing of FSM for

GMT project in advance

For FSMP

Use a model very close to FSM FSM prototype in KGMT project

Fabrication of FSMP with its own working cell designed by KRISS

Optical testing of FSMP after assembly with a cell (very close to real

FSM cell)

4

Recent experiences @ KRISS

800 mm lightweighted mirror for space application (1/2)

Gravity

Quilting (30 g/cm2)

And other environmental effects …

5

Recent experiences @ KRISS

800 mm lightweighted mirror for space application (2/2) - Measurement of wavefront error with two different methods : CGH (computer generated hologram) and conventional null lenses

CGHConventional null lens

/30 rms

6

1 m off-axis paraboloid for collimator (1/2) - Focal length = 6 m - Distance between the center of OAP and optical axis = 700 mm

Recent experiences @ KRISS

Flat mirror

Interferometer

OAP

7

1 m off-axis paraboloid for collimator (2/2)

Reference flat Interferometer

OAP mirror

Alignment telescope

Recent experiences @ KRISS

8

Fabrication facilities in KRISS

Rotating table with aspheric surface under test

Measuring tower with null interferometer

2 m CNC machine

1 m polishing machine

2 m coating chamberAssembly room

0.6 m polishing machine & testing tower

2 m polishing machine

9

Manufacturing flow diagram

Curve Curve generationgeneration

Curve Curve generationgeneration

Chemical Chemical EtchingEtching

Chemical Chemical EtchingEtching

Assembly Assembly with cellwith cell

Assembly Assembly with cellwith cell FATFATFATFAT

10% larger size 10% larger size Mirror blank Mirror blank procurementprocurement

10% larger size 10% larger size Mirror blank Mirror blank procurementprocurement

LightweightingLightweightingLightweightingLightweighting

PolishingPolishingPolishingPolishing GrindingGrindingGrindingGrinding InspectionInspectionInspectionInspection

InspectionInspectionInspectionInspection

Figuring Figuring (98%)(98%)

Figuring Figuring (98%)(98%)

InspectionInspectionInspectionInspection

Rounding to Rounding to target target

dimension dimension

Rounding to Rounding to target target

dimension dimension

Final Final figuring figuring

Final Final figuring figuring

10

SpherometerProfilometer

~ mm

Grinding

ProfilometerInterferometer

~ μm

Polishing

Interferometer with CGH

~ nm

Figuring

Scheme of Optical testing

Efficient testing process is a key for successful fabrication of mirror

11

KRISS profilometer

Measurement accuracy ~ 1 um Compensation of measurement errors of probe system using a high quality reference mirror

Reference mirror

150 mm

CGH layout :(Line spacing : ~ 20 um)

Adjustment between interferometer and CGH

Test configuration of FSMP off-axis segment (off-axis type CGH )

Interferometric testing using CGH

12

3

4

Adjustment I between CGH and FSMP segment

Adjustment II between CGH and FSMP segment

CGH alignment

12

3

4

14

Turn-over tool

KRISS Profilometer

Testing tower setup

15

Optical testing during fabrication Optical testing after assembly with FSMP cell

Testing configuration

Concept for working cell design

Minimization of print through Load cell on the back plate of the mirror 24 axial support location Polishing pressure at the pocket of mirror with 0.1 psi

FE Model of M2

Thin shell elements Material : Zerodur Diameter : 1064 mm Thickness : 140 mm Hole size : 100 mm Mass : 94 kg Face sheet : 20 mm Back plate : 14 mm Rib : 5 mm Web : 10 mm

Top view

bottom view

Axial support

x

y

support Radius (mm) Force (N)

Ring 1 157.5 21

Ring 2 242.5 33

Ring 3 367.5 42

Ring 4 424.4 58

Support locations

Print through

Gravity z

Displacement PV 165 nm

Surface error Without correction

PV 166 nmRMS 48 nm

Surface error With correction

PV 50 nmRMS 9 nm

Print through

Gravity z

10-2

10-1

100

101

102

101

102

103

separation (cm)

rms

wav

efro

nt e

rror

(nm

)

Structure function of M2

M2 structure function

Surface error

Quilting effect from polishing pressure of 0.1 psi

Surface error Without correction

PV 110 nmRMS 31 nm

Surface error With correction

PV 35 nmRMS 6 nm

Displacement PV 110 nm

Surface error

Polishing pressure 0.1 psi

10-2

10-1

100

101

102

101

102

103

separation (cm)

rms

wav

efro

nt e

rror

(nm

)

Structure function of M2

M2 structure function

23

Future works

Manufacturing of two types of CGH Manufacturing of testing tower Optimization of mirror working cell Fabrication of FSMP by the end of next year

We hope to take parts in the fabrication of FSM in future