Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

Transcription

1 Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

2 Overview of CAT-GS Mission requirements: Effective area > 1000 cm 2 (0.3 1 kev) Spectral resolution E/ΔE > 3000 (FWHM) Implementation: CAT grating array aft of mirrors (< 6 kg) Linear CCD detector array (32 CCDs) on instrument bus (< 40 kg) Flight mirror assembly view Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

3 Transmission Grating Spectrometer Heritage: Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

4 Diffraction Gratings for X-ray and EUV Spectroscopy Transmission Gratings Blazed Reflection Gratings Relaxed alignment & surface flatness tolerance Low diffraction efficiency (absorption, etc.) High diffraction efficiency Requires precise alignment, flat & smooth surface Grating Equation mλ = p(sinα + sin β ) m m: diffraction order λ: wavelength p: grating period α: incident angle, β m : diffracted angle Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

5 Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

6 Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

7 Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

8 Diffraction efficiency comparison bw. Chandra and CAT gratings Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

9 Mirror only (12.5 HPD) Observatory (15.0 HPD) Effect of sub-aperturing on resolution (Courtesy Andrew Rasmussen) λ/δλ ~ 2200 λ/δλ ~ 1350 Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27, 2009

10 Short history of the Space Nanotechnology Laboratory at MIT - Fabricated 200 (HEG) and 400 (MEG) nm-period Au transmission phase gratings for Chandra HETGS (> 500 gratings, > 1in 2, ) - SNL gratings flown on other missions: - SOHO (1995) - IMAGE (2000) - GOES N, O, P (2004, 2007, 2008) - TWINS A,B (2004, 2006) - Developed advanced high-precision grating patterning and nanofabrication tools and techniques Silicon CAT gratings Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

11 MIT Nanoruler Scanning-Beam Interference Lithography Tool Uses phase-locked, scanning beams to pattern large substrates (up to 300 mm) Tight control of grating phase & duty cycle (< 3 nm) Can pattern up to 5000 l/mm Recently demonstrated spatial frequency division which enables patterning up to 20,000 l/mm Heilmann et al., Nanotechnology 15, S504 (2004). C.-H. Chang et al., Opt. Lett. 33, 1572 (2008) Nanoruler with 300 mm silicon wafer Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

12 Nanoruler II 91 cm x 42 cm pulse compression grating Plymouth Grating Laboratory Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

13 Diffraction Gratings for X-ray and EUV Spectroscopy Transmission Gratings Blazed Reflection Gratings Relaxed alignment & surface flatness tolerance Low diffraction efficiency (absorption, etc.) High diffraction efficiency Requires precise alignment, flat & smooth surface Grating Equation mλ = p(sinα + sin β ) m m: diffraction order λ: wavelength p: grating period α: incident angle, β m : diffracted angle Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

14 How do you go from a blazed reflection grating to a blazed transmission grating? 2m+1 1m 0m-1 0 Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

15 Critical-Angle Transmission Gratings Oblique incidence, normal grating bars Normal incidence, tilted grating bars Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

16 Critical Angle Transmission (CAT) Grating Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

17 Critical-Angle Transmission (CAT) Grating Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

18 CAT Grating Design Issues Design Parameters (IXO) Period, p = 200 nm (large dispersion) Duty cycle (b/p) = 0.2 (high throughput) Critical angle, θ = 1.5º (high reflectivity) d = a/tanθ = 6 µm (optimum filling ) Sidewall roughness < 1 nm (high reflectivity) Fabrication Challenges High aspect ratio (d/b ~ 150) Thin grating bars (b = 40 nm) Freestanding structure Smooth sidewalls (roughness < 1 nm) Fine period gratings (p = 200 nm) Initial prototype: p = 574 nm, d = 10 μm Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

19 Recent 200 nm-period CAT grating fabrication results - Smaller period - Smaller sidewall angle - Higher etch anisotropy - Larger process latitude - Larger open area (> 45%) Scanning electron micrographs: (a) Top view (b) Bottom view (c) Cross section (destructive) As of January 2009: IXO design parameters achieved: d = 6 μm, <b> = 40 nm Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

20 Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

21 -2-3 Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

22 First x-ray data from 200 nm-period CAT gratings intensity [arb. units] nm 1.6 nm 2.4 nm nm nm 17.5 nm α ~ 2.6 o - strong blazing - reduced blazing for λ with θ c (λ) < α -0 th order transmitted at shortest wavelengths (CAT grating becomes weak phase grating) α = 2.6 deg (blaze 5.2 deg from 0 th order) Raw data (not normalized) detector angle [deg] Heilmann et al. Proc. SPIE 7011 (2008) Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

23 Normalized Diffraction Efficiency Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

24 efficiency wavelength [nm] 0th order -1st order -2nd order -3rd -4th -5th -6th -7th -8th -9th -10th order 0th order -1st order -2nd order sum(-1:-10) sum on det. Model calculations: Silicon CAT grating p = 200 nm θ= 1.5 deg 20 m focal length: 78 cm CCD array (32 CCDs) th order -1st order -2nd order 0.7-3rd order -4th 0.6-5th efficiency th -7th -8th -9th -10th order th -12th -13th sum(-1:-10) sum on det. energy [kev] Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

25 The CCD array covers a range of m*λ = 7.2 nm to 15 nm mλ = p(sinα + sin β ) m 0.7 efficiency m*lambda [nm] Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

26 Order Sorting Capability of CAT-GS detector read-out at blaze Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

27 Baseline CCD for CAT MIT/Lincoln, 1024 x 1024, 24-micron pixels, 4 outputs High-performance backside treatment On-chip binning for nominal ~50 fps readout rate Chandra/Suzaku heritage: ~100 CCD-years on-orbit & counting Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

28 Detector Array Linear array of 32 CCDs (25 mm x 25 mm, 24 μm pixel size) Mass: Camera kg (depending on shielding requirement) Detector electronics and power supply (DEA) 22 kg Digital processor 14 kg Power: Camera DEA Digital processor 5 W (thermal control) 28 W 20 W Courtesy David Robinson Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

29 Resolution (FWHM): black CAT-GS <R> ~ 3000 red XMS (ΔE = 2eV) BUT: for A = 1000 cm 2 subaperturing provides R = 4500 Figure of Merit sqrt(a*r): black CAT-GS <R> ~ 3000 A = 3000 cm 2 red XMS (ΔE = 2eV) green no gratings For more detail and response files go to Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,

30 Summary - CAT grating spectrometer easily meets & exceeds IXO requirements - CAT gratings combine advantages of transmission and blazed reflection gratings (low mass, relaxed alignment tolerances, high resolution, polarization insensitive - CAT-GS opens window into high-resolution soft x-ray spectroscopy Technology development: Increase open area (pre-etch techniques, etc.) Increase grating size (hierarchical support structures) Acknowledgements Eric Gullikson, Bob Fleming, Kathy Flanagan, Andrew Rasmussen, Chih-Hao Chang, Yong Zhao NSL & MTL (MIT) NASA ROSES APRA, Samsung scholarship program, Kavli Instrumentation Fund Ralf K. Heilmann CAT-GS: Critical-Angle Transmission Grating Spectrometer January 27,