NSLS II Metrology R&D Activities

1. NSLS II Metrology R&D Activities Peter Z. Takacs Experimental Facilities Advisory Committee Review 20 Oct 2006

2. Rationale for Metrology R&D for NSLS II • Every new advance in SR source design has driven improvements in optical components: • Pre-NSLS (<1980) SR mirror slope error quality: >2 arc sec (10µrad) • Original NSLS mirror specs: 1 arc sec (5µrad) for <10µm spot size. • This was difficult for manufacturers to achieve • NSLS upgrade: 1 µrad for <1µm spot size. • This is now routine • NSLS II requirements are now 100 nrad (!) • “If you can’t measure it, I can make it.” - Norm Brown, LLNL, 1980s • BNL developed the metrology to force manufacturers to improve their fabrication processes: surface roughness, then slope error • We need to do it again.

3. Where are mirrors in NSLS II beamlines? • X-ray scattering/crystallography - KB mirrors, bendable • Small-angle x-ray scattering (SAXS) - KB primary pair and KB secondary pair, both bendable • Scanning transmission x-ray microscope (STXM) - spherical grating monochromator (SGM) and steering mirrors for beam line branches. • High resolution inelastic x-ray scattering (IXS) beam line - spherical collimating mirror after pre-mono and KB pair after the high-res mono. • Superconducting wiggler - vertical focusing mirror for 50-100keV photons. • Soft x-ray beam lines - collimating and focusing optics Gratings, spheres, cylinders, paraboloids, ellipsoids, etc. Add “real world” slope error to soft x-ray beamline KB mirror surface:

4. Challenges in NSLS II mirror development • Need to develop reliable source(s) of nm-quality mirror components. • Work with vendors to insure required mirror parameters are met. • Provide metrology feedback • Need to develop in-house metrology instrumentation and techniques adequate for nm figure and 100nrad slope errors. • Plan for mirror metrology R&D -- near-term and longer-term tasks: • Develop Next-Generation Long Trace Profiler for reliable 100nrad measurements. • Develop stitching interferometry system for high-resolution figure over complete 2D surface area of mirror. • Evaluate new polishing techniques • QED MagnetoRheological Finishing (MRF) • Develop in-situ LTP for beam line diagnostics • At-wavelength testing capability

5. 1. Next Generation LTP • Present LTP III limited by systematic errors at the 1-2 µrad level. • Need to improve internal optical components and air bearing stage. • Glass quality affects measurement accuracy • Replace commercial PBS with custom PBS - $5K to $20K estimates • Replace Al beam (100µrad err) with ceramic beam (<5µrad err) • New linear motor drive system • 2D camera • Explore high resolution LTP options for spatial periods <1mm BNL LTP III measuring Si cylinder

6. NG-LTP: Resources required • Zygo Wavelength-shifting PMI required for internal glass quality measurement. • New technique allows separation of front and back surface from interior • NewView Micro-PMI (or equivalent) required for surface roughness control of internal LTP components. • Essential for replacement of defunct MicroMap profiler (vintage 1985) • Also use for profilometry of mirrors and quantitative topography of nanostructures, e.g. refractive kinoform optics • Also requires software development to add 2D camera and speed data acquisition. • Collaboration with LBL • Software development • Quantity discount in custom optics procurement

7. 2. Stitching metrology development QED SSI uses conventional Zygo Fizeau interferometer head combined with 6-axis positioning manipulator. Measured and predicted 40nm image shape from SSI on 100mm long elliptical cylinder. Yumoto,et al., RSI 76, 063708 (2005) • Subaperture stitching interferometry (SSI) necessary for 2D surface map • Required for deterministic surface info at ~50µm spatial periods • QED has the SSI metrology - companion to MRF machine. QED-developed algorithm solves for test surface error AND reference optics errors => self-calibrating, < 2nm residual errors. • Combine high resolution Fizeau PMI with LTP optical head. • Estimate 3 years to develop operational stitching system. View from interferometer in stitching of Osaka elliptical cylinder

8. 3. Polishing R&D Elastic Emission Machining Y. Mori, Osaka • Lessons from Osaka: • EEM technology 20 years in development • EEM can produce nm-level figure accuracy • Requires novel metrology techniques • Not (yet) available commercially. • BNL will NOT go into fabrication business. • We must rely on commercial optical fabricators • Need to explore new polishing technologies to achieve 100nrad optics • Need for in-house metrology instrumentation • Replacement needed ASAP for defunct MicroMap (former NCP-1000) for surface roughness measurement • Magnetorheological finishing (MRF) is most promising new technique for SR optics • Developed by QED Technologies, Rochester High speed rotating tool

9. 3. MRF polishing evaluation • Need to demonstrate Angstrom-level surface finish capability of MRF process. • Basic process limitations? uses diamond grit • Need to fine-tune machine parameters: slurry chemistry, dwell time • Establish collaboration with QED • Produce super-polished Si flat • Produce KB elliptical cylinders • Develop SSI metrology for non-rot symmetry parts • We will evaluate surface quality in lab and performance in NSLS and/or APS beam line. • Use NewView surface profiler and NG-LTP. • Requires stitching metrology software development for rectangular substrate shape. • Successful results => transfer technolgy to MRF-capable vendor. • Zeiss has expressed interest in meeting our needs • Heavily invested in MRF machines

10. Long-term metrology tasks • 4. In-situ LTP • In-situ LTP needed for beam line diagnostics. • Measure thermal and mechanical distortion on high heat load optics. • Look for transient heating effects on rigid body alignment. • Locate beam footprint on optical surface for alignment check. • Need to design essential interface ports into mirror chambers. • View through window normal to surface • Use scanning penta prism inside chamber • 5. At-wavelength metrology • Develop phase retrieval image evaluation system for x-ray wavelengths. • Similar to Souvorov technique at SPring8 • Useful for evaluating wavefront quality of various microfocusing optics • Zone plates, refractive optics, Bragg-Fresnel • Potential collaboration with J. Fienup at Rochester • Postdoc will be available in ~2yrs • Requires wavelength converter and camera hardware, software development • Test beam line would be useful for this and other at-wavelength methods.