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NGST IFU Prototype. Slit/Pupil Mirror Design. Original Design. Both Pupil and Slit mirrors required raster grinding to produce freeform surfaces in monolithic substrate Full tolerance analysis and specification produced. Pupil Mirror. Slit Mirror. Interim Design.

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NGST IFU Prototype

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Ngst ifu prototype

NGST IFU Prototype

Slit/Pupil Mirror Design

Original design

Original Design

  • Both Pupil and Slit mirrors required raster grinding to produce freeform surfaces in monolithic substrate

  • Full tolerance analysis and specification produced

Pupil Mirror

Slit Mirror

Interim design

Interim Design

  • IFU re-designed to eliminate need to use raster (freeform) grinding

  • Compromise in output slit performance (each “slitlet” focuses in different position in focal plane)

  • Considered easier by LFM to manufacture

Interim design pupil mirror

Interim Design – Pupil Mirror

  • Pupil Array Design

    • Zerodur Substrate

    • Monolithic Construction

    • Toleranced

    • Full Specification produced

    • Cost Estimate ~€12,000

Interim design pupil mirror1

Interim Design – Pupil Mirror

  • Slit Design

    • Construction as for pupil mirror

    • Fully Toleranced and specification produced

    • Cost estimate ~€12,000

Issues with manufacture

Issues With Manufacture

  • Development of Raster Grinding of Zerodur still in early stages of development

  • Proposed a “simplified” IFU design to use line contact method of grinding

  • IFU re-designed to accommodate line contact method of manufacture (but…)

Issues still remaining

Issues Still Remaining

  • Steps between Pupil/Slit facets will cause problems when grinding (unable to control quality/shape of surface close to step)

  • Either:

    • Larger gaps between facets

    • Modified grinding wheel (experimental)

Line contact grinding spherical

Line Contact Grinding (Spherical)

Line contact grinding toroidal

Line Contact Grinding (Toroidal)

Raster grinding

Raster Grinding

Grinding setup line contact

Grinding Setup (Line Contact)

Rougness measurement test component

Rougness Measurement (test Component)


Interferometry test component

Interferometry (test component)

  • This should have a picture of the interferometry data however including it crashes my laptop

  • Aperture 4mm x 6mm

  • Spherical – ROC = 66.2mm

  • PV : 0.174

  • rms : 0.023

Next stages zerodur optics

Next Stages (Zerodur Optics)

  • Produce spherical “proof of concept” monolithic mirror

  • Toroid production tests

  • Tackle issue of stepped facets

  • Produce line contact ground components

  • Develop raster grinding techniques

Timescale for development

Timescale For Development

  • To develop repeatable/reliable process for production of monolithic components in Zerodur (line contact method with steps between facets)

    – not possible before August 03

  • This gives a problem with IFU schedule



  • Develop IFU system with replacement metal (Aluminium) Pupil and Slit arrays

  • Perform all warm/vibration tests with metal components – replace with Zerodur when techniques fully developed

  • Durham shall provide metal components (already have much experience with GNIRS IFU)

  • Pursue Zerodur components in parallel

Gnirs ifu slit mirror

GNIRS IFU Slit Mirror

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