Characterisation of a novel super-polished bimorph mirror Kawal Sawhney 1, Simon Alcock 1, Hongchang Wang 1, John Sutter 1 and Riccardo Signorato 2 1 Diamond Light Source Ltd. UK 2 BASC, D-51429 Bergisch Gladbach, Germany Kawal.sawhney@diamond.ac.uk ACTOP11, Apr 11
Outline Motivation & Concept Metrology testing (Diamond-NOM) X-ray testing (Beamline B16) Summary and future
The ideal synchrotron mirror Pure focal spot Ellipse with slope & figure error ~100nrad & ~1nm rms Adaptive Change focal distance / size Correct upstream optical errors Remove heat-load / mounting deformations Can this be realised???
Next generation adaptive optics No single technique can provide flexibility & quality, so combine two! Super-polished substrate: mid & high spatial frequency roughness (JTEC) Piezo bimorph (8 channels): figure / slope error (SESO) Adaptive optic with exceptional quality Micro- & nano-focussing Coherence preservation Wavefront correction,
Super-Polished Bimorph 8 piezo bimorph (SESO), 150mm long, fused silica substrate EEM treatment (JTEC) on central ~120mm [Figuring with sub nanometre-level accuracy by numerically controlled elastic emission machining, K Yamauchi et al, Rev. Sci. Instrum. 73, 4028 (2002)] Elliptical pre-figure (p=41.5m, q=0.4m, θ=3mrad) Height error before and after EEM polishing JTEC, Osaka novel super-polished bimorph mirror
Super-Polished Bimorph < 0.5 nm rms (< 2 nm PV) height error! 0.1 µrad rms slope error! < 0.1 µrad rms slope error! Error profiles along the tangential direction from the nominal ellipse No bimorph corrections applied! JTEC, Osaka
Figure Error Figure error < 1nm rms p=41.5m, q=0.4m, θ=3mrad Diamond NOM Slope error ~0.15 µrad rms
Micro-Roughness Diamond Micro-interferometer Objective Field of View EEM region Sq Non-EEM region Sq 2.5X 3446 x 2563µm 1.92Å rms No data 10X 864 x 643µm 2.03Å rms 1.83Å rms 50X 173 x 129µm 1.90Å rms 1.91Å rms No change in micro-roughness by EEM polishing
Range of Bending p = 41.5 55m, q = 200 400mm, θ = 1.22 3mrad Apply 300V. Does figure error worsen? Only by 1nm PV! Diamond NOM
B16 Test Beamline For testing optics & detectors For developing novel experiments & techniques Flexibility & versatility to enable wide range of experiments Large energy range (2 kev 25 kev) Several operational modes: mono, white, micro-focused, Range of beam sizes : 1 micron to 100 mm Experimental Hutch Optics: DCM Toroidal Mirror - DMM
B16 experimental Monochromatic, unfocused beam: 8 kev Double Multilayer Mono (Ni/B4C) for higher order suppression Detectors: Au-wire scan on piezo stage X-ray eye camera (for initial alignment) High resolution X-ray Microscope: (20x objective, 5µm-thick Eu:LuAG scintillator, PCO CCD camera, 0.18µm effective pixel size) Optics Table EEM Mirror Optique Peter
Preliminary X-ray Measurements B16 Mirror parameters: As fabricated : 41.4m 0.3m 3 mrad On B16 : 46.5m 0.3m 3 mrad Depth of Focus Variation of Bimorph Voltages All electrodes -100V of NOM 9 8 #21920-21929 Depth of Focus from wire scans 0.02 0.00 NOM NOM-100V 7-0.02 fwhm (um) 6 5 4 Derivative Y1-0.04-0.06 #21975, 21973 NOM 3 2-0.08-0.10 fwhm: 1.45 um NOM 1.22 um NOM-100V NOM-100V is more smooth 1 200 210 220 230 240 250 260 270 280 290 300 fwhmum(mm) -0.12 20 21 22 23 24 25 26 27 28 29 30 piezo1y Focal spot ~1.2 µm for NOM-100V
Measured Focus Size B16 Image & line profile using Optique Peter camera Derivative of transmission signal [a.u] 0.0-0.1-0.2-0.3-0.4 fwhm=1.2 µm Equation y=y0 + (A/(w*sqrt(PI/2)))*ex p(-2*((x-xc)/w)^2) Reduced Chi-Sq 2.47991E-4 r Adj. R-Square 0.97342 Value Standard Error Derivative Y1 y0-0.00458 0.00209 Derivative Y1 xc 25.32463 0.01385 Derivative Y1 w 1.06894 0.02887 Derivative Y1 A -0.52874 0.01327 Derivative Y1 sigma 0.53447 Derivative Y1 FWHM 1.25858 Derivative Y1 Height -0.39467 Au wire scan 20 25 30 Wire vertical position [µm] 0.75 0.60 0.45 0.30 0.15 0.00 Transmission signal [a.u]
Stability/ Reproducibility Tests B16 ~ 6 hours [0 V] on Bimorph Wait 10 minutes Perform wire scan Set Voltages derived from NOM Wait 10 minutes Perform wire scan Relative transverse focal position (µm) 65 60 55 50 Stability over 6 hours Red: No voltages Blue: NOM voltages ~ 0.6 um drift in 1 hour at 0 voltages ~ 0.8 um drift in 1 hour at NOM voltages 6 hours B ExpDec1 of B ExpDec1 of B 0 5 10 15 20 25 30 35 40 Time (a.u) No change in beam size Drift in peak position of <1 µm in 1 hour Cause of drift: bimorph / beamline?
Ex-situ Vs in-situ Slope error measured by Diamond NOM and slit scans on B16 B16 Good correlation between ex-situ (DLS-NOM) and in-situ (B16) measurements
Wavefront Characterisation using Shearing Interferometer Interferometer placed out of focus (E=14.8keV θ=0.05 ) Interferometer G 1 G 2 Detector
Shearing Interferometer: Moiré Fringe analysis method averages data along the whole width fov (~1.4mm) Miror slope difference tested with Diamond_NOM Wavefront slope difference tested with interferometer
Shearing Interferometer: Phase stepping method Wavefront Slope Mirror Length Mirror Width Phase stepping methods give high resolution for detailed information on wavefront divergence mismatch of the gratings Data still being processed
Summary / Future A novel super-polished bimorph mirror developed Characterised using Diamond-NOM and B16 Test beamline EEM gives elliptical shape with exceptional figure and slope error Bimorph provides wide range of elliptical shapes & sub-nm figure correction Preliminary X-ray tests performed on B16 Test beamline Slit scans, wavefront analysis, Use an ID beamline B16 : vary focal distance : out-of-focus beam (and minimise structures) : Wavefront analysis using shearing interferometer - use divergence matched gratings More tests on B16 in July 2011
Acknowledgments B16: Igor Dolbnya, Andrew Malandain, Slava Kachkanov Geoff Ludbrook for micro-roughness data Lucia Alianelli Christian David, PSI for providing the gratings for the interferometer JTEC (Japan) for their expert EEM polishing skills SESO (France) for designing & manufacturing high quality, custombuilt, bimorph optic Sincrotrone Trieste (Italy) for providing state-of-the-art, high voltage, power supply