Shaping Thin Glass Mirrors using Air Bearings
1 / 20

Shaping Thin Glass Mirrors using Air Bearings - PowerPoint PPT Presentation

  • Uploaded on

Shaping Thin Glass Mirrors using Air Bearings Mark L. Schattenburg , Mireille K. Akilian and Ralf K. Heilmann Space Nanotechnology Laboratory Kavli Institute for Astrophysics and Space Research Massachusetts Institute of Technology, Cambridge, MA 02139

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' Shaping Thin Glass Mirrors using Air Bearings' - vahe

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

Shaping Thin Glass Mirrors using Air Bearings

Mark L. Schattenburg, Mireille K. Akilian and Ralf K. Heilmann

Space Nanotechnology Laboratory

Kavli Institute for Astrophysics and Space Research

Massachusetts Institute of Technology, Cambridge, MA 02139

International Workshop on Astronomical X-Ray Optics

Prague, Czech Republic

Dec. 9, 2009

Thin sheet glass is produced in high volume with high quality
Thin Sheet Glass is Produced in High Volume with High Quality

Hard Disk Drives

Liquid Crystal Displays

Sheet glass manufacturing processes
Sheet Glass Manufacturing Processes Quality

Slot Draw Process

Corning’s Fusion Process

Traditional slumping technology
Traditional Slumping Technology Quality

  • Large thermal asymmetry:

  • Very long slumping cycles

  • Edge curl up

  • CTE mismatch ripples

Problems with conventional slumping technology
Problems with Conventional Slumping Technology Quality

  • Sticking

  • Dust particles, ripples …

  • Large thermal asymmetry

  • Long thermal cycles (days)

The traditional approach is not working …

We need a new idea!

Glass sheet slumped on dusty mandrel

Problem: How to faithfully replicate mandrel surface. QualitySolution: Porous air bearing prevents glass from touching mandrel.

Glass surface from manufacturer

Glass surface after slumping

Flatness ~400 μm P-V (Peak-to-Valley)

Flatness <0.4 μm RMS

Air bearing slumping concept
Air Bearing Slumping Concept Quality

Glass sheet is mechanically supported by tungsten wires

100 mm

Glass centerline is forced to bearing mid-point

Fluid dynamics governing equations
Fluid Dynamics Governing Equations Quality

Flow inside porous mandrel

Where k: permeability

p’: pressure in porous mandrel

p: pressure in gap

h: air gap height

H: porous mandrel thickness

Flow in gap

h = 15 μm

h = 5 μm

h = 10 μm

Glass is pushed to centerline with 1 h 3 restoring force
Glass is Pushed to Centerline with 1/h Quality3 Restoring Force

Assume: h is constant


Fact:permeability k << h2

h1 > h2 p1 < p2

Slumping onto flat surfaces easiest plan to start
Slumping onto Flat Surfaces Easiest Plan to Start Quality


  • Crawl: Slump onto flat mandrels:

    • Low cost mandrels

    • Simplified metrology

    • Develop understanding of fluid dymamics

  • Walk: Slump onto Wolter mandrels (new effort)

  • Run: Continuous slumpingprocess

  • Prototype mandrel assembly concept
    Prototype Mandrel Assembly Concept Quality

    • Tantalum spacers maintain 50 mm glass-mandrel gaps

    • (temporary solution).

    • Spacers eliminated in future design.

    MIT-Kavli Institute

    Mandrel plumbing layout
    Mandrel Plumbing Layout Quality

    All experiments to date performed with open-loop pressure control.

    Closed-loop control has been implemented and is under test.

    Slumping results glass sheet surface metrology
    Slumping Results: Glass Sheet Surface Metrology Quality

    P-V 2.26 μm; RMS 0.39 μm


    RMS 12.22 arcsec

    RMS 7.53 arcsec



    Slumping repeatability sheet to sheet
    Slumping Repeatability: Sheet-to-Sheet Quality

    RMS 0.35 μm


    RMS 8.13 arcsec

    RMS 3.30 arcsec



    Deep-UV ( Qualityl=250 nm) Shack-Hartmann Metrology Tool

    Repeatability ~ 40 nm P-V

    Thin Optic Constraint Quality


    flexures (3)

    Silicon wafer

    Reference block


    55 nm

    Vertical tilt stage

    Antenna flexures (4)

    Horizontal tilt stage

    The next steps for air bearing slumping
    The Next Steps for Air Bearing Slumping … Quality

    • Implement closed-loop pressure control.

    • (Completed and under test.)

    (3) Develop continuous processing

    of Wolter Optics

    (2) Eliminate spacers

    Summary Quality

    • Demonstrated a new method for slumping glass using porous air bearings.

    • Eliminates high-frequency errors due to dust particles

      1/h3 restoring force.

    • Demonstrated sheet-to-sheet repeatability of 3.3 arc sec.

    • New funding source obtained (2010-2014)

      Two new Mech. E. Ph.D. students hired

      Larger slumping facility under development

      We are grateful to the NASA ROSES program

      for financial support.