Applications Et Realisations De La Technologie Plasma Reactive Atom Plasma (RAP) Pour La Fabrication De Grands Optiques R. Jourdain, M. Castelli, P.

Transcription

1 Applications Et Realisations De La Technologie Plasma Reactive Atom Plasma (RAP) Pour La Fabrication De Grands Optiques R. Jourdain, M. Castelli, P. Morantz, P. Shore Cranfield University, Precision Engineering Centre,

2 Content Aim and objectives Competing technologies Fabrication chain for large optics RAP technology & RAP process RAP figuring results Summary 2

3 Some Facts and Figures Specialist postgraduate institution 3,500 students & 4,500 qualified professionals Strong links between teaching, research and innovation The UK s only wholly STEM focused Postgraduate University 75% of all aerospace engineering postgraduates in the UK graduate at Cranfield 10% of the UK s engineering and sciences PhDs are awarded by Cranfield 3

4 Aims and Applications HiPER (England) Laser Mega Joule (France) National Ignition Facility (USA) Laser fusion program metre scaled optical component Texture < 1 nm RMS Earth orbiters Figuring process Form accuracy <10 nm RMS European Extremely Large Telescope 8 Hours processing time 4 Extreme Ultra Violet Lithography

5 Roughness [nm] RMS Precision Optical Processes 1000 Fixed Abrasive Grinding Ductile Mode Grinding Computer Controlled Polishing Ion Bean figuring Magneto Rheological Finishing Reactive Atom Plasma (RAP300 RAP1200) Material Removal Rate [mm 3 /min] 5

6 Possible processing route metre scale optical component Stage 1 Stage 2 Stage 3 Surface roughness < 1 nm RMS Grinding process 1 mm form accuracy 1 μm form accuracy Polishing RAP process process 300nm form accuracy Form accuracy <10 nm RMS BoX / Ultra precision grinding Polishing machine Helios1200 / Figuring machine 6

7 MRR [ mm 3 /min ] RAP process Reactive Atom Plasma is a dry chemical etching process developed to figure silicon based optical surfaces at atmospheric pressure. Reactive Atom Plasma ULE fused silica Materials such as Si, ULE, Borosilicate, fused silica, SiC can be processed Travelling speed [ mm/min ] 7

8 RAP process -Dwell time 10x1sec - FWHM 11mm - Outer diameter 25mm RAP plume Footprint - Reduced heat transfer - Low contamination - Easily tuneable - Power can be increase - Reliable and deterministic -De-Laval nozzle RAP Torch (RAP1200) 8

9 RAP machine - 3 axis - CNC FANUC controller. - Dedicated software. - Dwell time based tool path algorithm. - Double skin sealed unit. - Scrubber Helios 1200 (Overview) - Optical component facing down - No clamping mechanism. - Can load more than one components - Loading time is about few minutes Helios 1200 (processing capability) 9

10 Tool Path Algorithm The surface is raster-scanned following a reversed staggered meander-type tool-path algorithm. Processing conditions and first tool motion loop are illustrated in the left schematic YY ZZ XX 10

11 RAP Processing time 100mm diameter surface Measurement time [min.] 30 Computational time [ min.] 20 Torch startup-time [ min.] 3 Sample loading time [ min.] 5 Figuring time [ min.] 6 Processing time Processed area Assessed area Roughness after RAP processing (0.5um removal) Roughness after polishing: S a = 1.8nm 11

12 RAP Surface figuring results RMS: 139nm RMS: 31nm Surface profile deformation before processing Targeted surface figure Processed surface profile Results RMS: 31nm Processing time 2x 6min Convergence ratio of about 78 percent RMS: 31nm 12 Residual surface error Interferogram

13 RAP Surface figuring repeatability FINAL SPHERICAL HOLLOWS 31 nm rms 31 nm rms 16 nm rms 16 nm rms RESIDUAL FIGURE ERROR MAPS 13

14 RAP Surface figuring on 6 inches 128nm rms 500nm PV 18nm rms 146nm PV 128 RMS down to 18nm RMS 6inch sphere 79nm rms 374nm PV 16nm rms 158nm PV 79 RMS down to 16nm RMS 6inch flat 14

15 Processing time (hours) Processing time for metre class segmented mirrors and NIF wedge focus lenses Feed Speed (m/min) Scenario: Material removal of a 0.5um thick layer. Processing time prediction based on experimental results involving turbo torch on fused silica material. 15

16 Summary Achievements Development of a new fast figuring process Figure correction: better than Lambda/40 over 6 Development and optimisation of tool path algorithm Understanding of processing parameters Metre scale operational figuring machine Further work Scaling up figuring capability Up to 8 for free form surfaces few micron deep (August) Up to 16 for three metre ROC (November) 16

17 Thank you for your attention! 17