0.1-meV Optics Update: Progress, Challenges, and Future Plan

1. 0.1-meV Optics Update Yong Cai Inelastic X-ray Scattering GroupExperimental Facilities Division, NSLS-II Experimental Facilities Advisory Committee Meeting April 23-24, 2009

2. The IXS Group • Current Members • Xianrong Huang, 0.1 meV crystal optics • Marcelo Honnicke, multilayer mirrors for analyzer system • Jeff Keister, R&D beamline operation, upgrade and support • Zhong Zhong, NSLS D&I beamline spokesperson (M) • Scott Coburn, engineering design (50%) • Leo Reffi, mechanical design (on loan from design group) • Bill Struble, crystal cutting and lab support • Yong Cai, IXS beamline, group leader • Future Members (per staffing plan) • Postdoctoral Fellow (Crystal fabrication, optics testing, etc.) – offer accepted, to start around June 1 • Scientific Associate (Crystal fabrication lab) – Searching • Beamline Scientist (IXS beamline) - Searching

3. Outline Summary of progress to date, issues & plan Current optical scheme and technical challenges Near-term milestones and longer-term plan Summary

4. Summary of Progress to Date, Issues & Plan Since last EFAC Meeting (May 5-7, 2008) • Major progress in building up the infrastructure to support the R&D program • R&D beamline and optics test end station at NSLS (X16A) • Crystal fabrication labs (Bldg 703) • R&D activities have been focused on gaining a better understanding of the technical requirements and challenges of the optics • 0.1meV crystal optics • Multilayer mirrors • Issues and plan • Crystal fabrication capabilities (equipment & staffing) • Access to more advanced light source(s) for prototyping

5. 0.1meV Crystal Optics • CDW and CDDW optics schemes at 9.1 keV proposed by Yu. Shvyd’ko, verified by our dynamical theory calculations (Xianrong Huang) CDW CDDW • Large angular acceptance (>100 µrad) • High efficiency (~50%) • Sharp tails (Borrmann effect), more important than resolution! 0.11 meV

6. Beamline and Spectrometer Optics Layout ~20 μrad Divergence • Major parameters determined and verified for E = 9.13 keV, Δθe = 5 µrad, and h = 0.5 mm • Comb crystal proposed by Yu. Shvyd’ko: a possible solution to the long D crystal length, but a major challenge to fabricate (in progress)

7. Comb Crystal Fabrication Current approach employed by APS: Cut directly from a monolithic crystal. Polishing the diffraction surface a major challenge. Alternative approach to be explored: Prepare reference Si(100) surface from a monolithic block Cut individual fins allowing fine polishing of diffraction surface Align individual blocks using reference surface on symmetric backscattering Si(800) reflection Mechanical positioning a challenge, but more solvable As-cut surface roughness 35.4 nm by AFM Reference Si(800) reflection Fine polishing Tilting  (rad) Θ Reference surface 100mm 5mm

8. CDDW for 1meV + Channel Cut 5 Collimated 20rad Channel-cut (grazing 7) • No need for long D crystal • Switchable between 0.1 and 1 meV • Require incident beam collimated to ≤20 rad no problem for monoanalyzer needs high-precision mirror. • CC causes ~20% efficiency loss Tails sharper than Lorentz

9. Other Major Technical Challenges • Lattice homogeneity of the crystal: d/d = ΔE/E ~ 10-8 (0.1 meV/10 keV) • Temperature uniformity and stability: ΔT ≤ 4 mK (Δd/d = αΔT and thermal coefficient of Si: α=2.5610-6 K-1) • Surface qualityslope errors (straightness of surface): < 10 µrad, crystal bending (due to mounting or gravity sag): < 0.2 µrad, surface roughness (causes diffused scattering): < 2 nm • Crystal angular stability: < 0.2 µrad as a result of energy tuning by angular rotation, independent of resolution 0.1 – 1 meV, • CDW/CDDW analyzer requires 50~100:1 multilayer focusing mirrors for 5~10 mrad acceptance

10. Angular Stability • Energy Tuning by D crystal rotation : Tuning rate: 0.07 meV/µrad • This implies also: • Angular vibrations of C,W, D all change , must be stable < 0.2 rad (independent of targeted energy resolution E) • Lattice bending due to gravity sag or mounting changes , so must be < 0.2 rad, for all C, W, D.

11. Laterally Graded Multi-layer Mirror • Design Objectives: • Angular acceptance: 5 mrad x 5 mrad • To retain a q resolution of 0.01 nm-1 • Corresponding to ~0.1 mrad in horizontal acceptance at 9.1 keV or 20 µm transverse width at 200 mm from source. Possiblesolution: use area detector! • Laterally projected source size due to sample thickness may be a limiting factor, but not a severe problem due to lessen q resolution required at higher q. (0.1 mrad = 20 µm projected source size at 200mm) 0.2 – 0.3 mm CDW or CDDW Strip Detector 0.1 mrad 5 mrad Horizontal Scattering Plane

12. Ideal Mirror Figure • Parabolic ellipsoid (focusing collimator) • Horizontal collimation to 0.1 mrador better is required in order to retain the q resolution! • Vertical focusing (up to 0.1 mrad) to minimize D crystal length for analyzer, but may limit the horizontal q resolution at low q. • Vertical collimation to less than 20 µradmay allow the use of 2nd channel cut for resolution switching between 0.1 and 1 meV for the analyzer, and/or possible energy dispersive and q resolved detection in the vertical direction with an area detector • A real challenge to make! • Sample – first focus (f1) • Sample • CDW/CDDW

13. Alternative Mirror Configurations • A single toroidal mirror to approximate the ideal surface • Montel optics: parabolic (collimator) in a double bounce geometry (involving beam inversion of L-R and U-D) • KB configuration • A single mirror only for vertical focusing/collimating • Horizontal angular acceptance of C crystal ~ 3mrad!Horizontal energy dispersion of D crystal: E(φ) = E0(1-φ2/2) • Montel Optics (collimating) 0.2 m 10 m

14. Other Works Accomplished Multilayer parameters determined and optimized both for parabolic and elliptical figures. Mirror specifications for a non-graded flat surfaceSi or B4C layer 1.5 nm, W layer 1.0 nm, 100 bi-layers on Si substrateTheoretical peak reflectivity: 85% Figure specifications In-house ray-tracing codes developed to examine performance of the multilayer mirrors including effects of slope error, roughness, and interlayer thickness fluctuation (δd/d). Actively in contact with possible vendors for test mirrors Test plan using R&D beamline at NSLS developed.

15. First CDW-CDW Test at NSLS • Proof of Principles: • Collimation effect of C crystal • Enhanced Bormann transmission of W crystal • Most importantly, the dispersion effect of the D crystal • E = 10 meV achieved, possible causes being analyzed D C,W Tilting  (rad) ΔE = 10 meV

16. New CDW-CDW Test • Aim for a more controlled study of the optics to understand conditions to achieve the targeted energy resolution. • Verify sharp tail in resolution functionwith new optical path • New C/W crystal to minimize strain Bill Struble’s first crystal With help from Shu Cheung

17. Optics Test End Station D crystal in oven C/Wcrystal • Current components designed to test CDW-CDW scheme with temperature control ovens • Include a double-crystal diffraction / imaging stage for characterizing crystal quality • Flexible and adaptable for other schemes (e.g., CDDW, comb crystals, …) • Most components fabricated and assembled, and being installed on R&D beamline

18. Temperature Control Oven Room T D crystal Outer Oven, ΔT ≤ 0.5 mK Inner Oven, ΔT ≤ 0.25 mK ~15 hr • First oven tests: passive controlling on both inner (~45 C) and outer (~35 C) ovens. • Excellent stability; uniformity to be tested.

19. Dedicated R&D Beamline at NSLS An existing PRT beamline, revived after major clean-up and repair effort of shielding, vacuum, safety and user interlock, beamline and endstation control, to allow initial testing of 0.1 meV resolution optics Existing beamline optics (a 1:1 focusing mirror and a DCM) found to be functional but required optimization, to be upgraded within 6-12 months. Beamline granted operation status since April 10, 2009 after beamline review and readiness walkthrough. (took just 1 year from inception to operation, but still a lot of work!) Endstation Mirror(1:1) Source Mono R&D beamline assembly

20. Crystal Fabrication Labs EQUIPMENT • Two labs being fit out, to be completed in April: • Cutting / Lapping Lab major equipments: • Crystal Diffractometer (NSLS equipment) • Mark Blade Saw (NSLS equipment) • Diamond wire saw (delivered) • Lapping machine (delivered) • Strasbaugh Spindle Polisher (rough polishing) • Polishing / Etching Lab major equipments: • ADT dicing saw (delivered) • Strasbaugh CMP polisher (superfine ~ 0.1 nm) • Strasbaugh Spindle Polisher (fine polishing) • Chemical etching hood and wet bench • Partial operation in April • Need to consolidate fabrication equipment and streamline fabrication process • Too few staff with expertise in polishing and etching X-ray Diffractometer / Blade Saw / Diamond Wire Saw Lapping Machine / Spindle Polisher / CMP Polisher High-precision dicing saw for Comb crystal fabrication Etching Hood

21. Overall Strategy and Near-Term Milestones Overall strategy and timeline: 2009 2010 2011 CDW/CDDW prototypes 1meV0.5meV0.1meV Comb crystals fabrication and test Design and Develop collimating multilayer mirrors 0.1 meV prototype spectrometer

22. Longer-Term Plan & Milestones 2010 • Develop a prototype with 1meV resolutionStrategy being considered: a Partner User Proposal with APS for Sector 30 • Demonstration experiments on Plexiglas with 1meV resolution (real test of energy resolution and tail by scattering rather than diffraction) • Full work on CDDW prototype to test 0.5 meV resolution (with comb crystals), including detailed exploration of crystal quality (defects, impurities, inhomogeneities), fabrication issues. • Test and improve collimating/focusing multilayer mirrors • Seek alternative approaches if encounter unexpected showstoppers • 2011 • Test and improve analyzer optics with multilayer mirrors • Full work on CDDW prototype to test 0.1 meV resolution (with comb crystals) • Finalize design

23. Summary Excellent progress has been made in establishing the essential infrastructure to support the R&D program. Initial test results of the asymmetric dispersion optics prove the working principles of the optics. Key technical challenges to achieve the 0.1meV resolution for both the monochromator and analyzer are now well understood and being addressed. Need to streamline crystal fabrication capability within the NSLS-II project, and for prototyping a 1meV resolution instrument. A modified approach with intermediate staged goals may be necessary for the development of the IXS beamline.