# Presentation: 716401

## Hybrid Mirror Optical Processing and Metrology

**Eric Ruch  SAGEM**

## NMSD Hybrid Mirror

**Glass Meniscus.**
**Polishing Strategy.**
**Testing Strategy.**
**The Sub Apertures Measurements.**
**Cryo Test Results.**

## Glass Meniscus

**Plano - Plano Zerodur Blank: 30 mm thick**
**Hexagonal outer contour shaping**
**Plano - Concave shape:**
**Front concave surface milling, grinding and polishing**
**Meniscus shape:**
**Back convex surface milling down to 5 mm thickness**
**Back convex surface grinding down to 3 mm thickness**
**Back surface polishing**

## Granite Blocking Body

**Convex granite: spherical shape with about 6 μm accuracy**
**Vacuum grooves to hold the meniscus during processing**

**Granite Blocking Body**

## NMSD Mensicus on Granite

**NMSD Mensicus on Granite**

## NMSD Meniscus Grinding

**NMSD Meniscus Grinding**

## NMSD Polishing Strategy

**The Polishing Strategy must be able to:**
**correct for the meniscus distortion induced by the bonding.**
**limit the quilting effect of this extreme lightweighted structure.**
**The polishing strategy is demonstrated on a 300 mm flat subscale mirror.**
**The selected polishing process:**
**Low pressure polishing technique.**
**Ion - Figuring.**

## NMSD Mirror Polishing

**NMSD Mirror Polishing**

## NMSD Mirror Polishing

**NMSD Mirror Polishing**

## In-Process Testing Strategy

**CMM Measurements:**
**High dynamic range, moderate accuracy, used in early stage of polishing.**
**IR Interferometry:**
**High dynamic range, medium range accuracy, used on poor polished surfaces.**
**Visible Interferometry:**
**SPSI has one of the largest dynamic range of the existing interferometers.**

##    CMM Measurements

**   ****CMM Measurements**

**Spatial resolution:**
**100 x 100 points**
**Vertical Resolution:**
**5 μm over 2 x 2 meters**
**Estimated Accuracy:**
**5 μm RMS.**
**Measurement Duration:**
**2 hours**

## NMSD Composite Pathfinder on Test Stand

**NMSD Composite Pathfinder on Test Stand**

##    NMSD IR Fringes

**   ****NMSD IR Fringes**

**Spatial resolution:**
**100 x 100 points**
**Estimated Accuracy:**
**1 μm RMS.**
**Measurement Duration:**
**8 hours**

##    IR Interferometry

**   ****IR Interferometry**

## SPSI Full Aperture Interferometry

**SPSI Full Aperture Interferometry**

**Spatial resolution:**
**500 x 500 points**
**Estimated Accuracy:**
**0,1 μm RMS.**
**Measurement Duration:**
**8 hours**
**Single Shot  Measure is not possible**

## SPSI Set-up

- Reference
- Sphere

- Folding
- Mirrors

## NMSD Predicted Quilting for Initial Optical Processing

##  Second Cryo Correction:  CMM Results

** ****Second Cryo Correction:  CMM Results**

##  Second Cryo Correction: IR Interferometry

** ****Second Cryo Correction: IR Interferometry**

##  Second Cryo Test

**The stitching process:**
**mirror fiducialization **
**18 individual sub-apertures measurements**
**Each sub-aperture is resized and positioned on the mirror surface**
**Surface reconstruction by least squares minimization**** **
**The stitching accuracy is function of:**
**the sub-apertures measurement accuracy.**
**the fiducials location accuracy.**
**the stitching algorithm accuracy.**
**estimated accuracy 0,2 μm RMS in NMSD case****.   **

## Sub Apertures

##   39K Measurement

**  ****39K Measurement**

##   60K Measurement

**  ****60K Measurement**

##   80K Measurement

**  ****80K Measurement**

## Ambient Measurement

**Ambient Measurement**

##   Second Cryo Test Results

**Measurement accuracy greatly improved wrt first test:**
**better surface finish **
**better cryo correction**
**The remaining cryo correction can be done by ion figuring.   **

##   Cryo Figuring Correction Simulation

**  ****Cryo Figuring Correction Simulation**