ngst ifu prototype

Manosque, 25 February 2003

University of Durham Astronomical Instrumentation GroupAstronomical Instrumentation Group

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

• 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

• Pupil Array Design– Zerodur Substrate– Monolithic

Construction– Toleranced– Full Specification

produced– Cost Estimate

~€12,000



Interim Design – Pupil Mirror

• Slit Design– Construction as for

pupil mirror– Fully Toleranced and

specification produced– Cost estimate

~€12,000



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• 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 (Toroidal)



Raster Grinding



Grinding Setup (Line Contact)



Rougness Measurement (test Component)

Ra=10nm



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)

• 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

• 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



Proposal

• 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

ngst ifu prototype

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