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SYNCHROTRON LIGHT SOURCE

SYNCHROTRON LIGHT SOURCE. grating monochromators. Josep Nicolas. 31.03.2005. What is a monochromator?. A device that transmits a single wavelength of the incoming radiation. “monochromatic” radiation. monochromator. “white” radiation. Photon #. Photon #. E = h n. E = h n.

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SYNCHROTRON LIGHT SOURCE

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  1. SYNCHROTRON LIGHT SOURCE grating monochromators Josep Nicolas 31.03.2005

  2. What is a monochromator? A device that transmits a single wavelength of the incoming radiation “monochromatic” radiation monochromator “white” radiation Photon # Photon # E = hn E = hn Bandwidth Range Efficiency

  3. Monochromator: Grating or Crystal ? Gratings monochromators Crystal monochromators G.I. N.I. UV VIS SXR HXR 2K 5K 30K 1.7 3 250 hn[eV] • Inter-atomic distance must be larger than diffracted wavelength • volume diffraction • A discrete number of wavelengths are reflected for a given incidence angle • Bragg Law equation • Gratings have low efficiency at HXR • Surface diffraction • A continuum number of wavelengths are reflected for each incidence angle • Grating equation

  4. 2 of the beamlines proposed to SAC for evaluation require grating monochromators XMCD XRMS POLUX (80-2000 eV) XPEEM EXES UV & SXR (150-1500 eV)

  5. Monochromators for XMCD Monochromator Facility Beamline Energy Range Resolution Flux on sample VLSPGM Spring 8 BL25SU 220 - 2000 ~10000 1.00E+11 SX700 ALS 4.0.2 52 - 1900 ~7000 UE56/PGM SX700 BESSY II 100 - 1200 ~6000 1.00E+12 SX700 MAXLAB D1011 30 - 1500 1500-13000 5.00E+10 PADMORE BESSY II UE52 90 - 1500 ~3000 1.00E+11 PADMORE ELETTRA BACH 35 - 1600 >5000 1.00E+11 VLS MIYAKE SOLEIL DEIMOS 350 - 2000 ~6000 1.00E+11 DRAGON VLS DIAMOND BLADE 400 - 2000 ~10000 DRAGON APS 4-ID-C 500 - 2800 >1000 1.00E+13 DRAGON ESRF ID8 500 - 1500 ~5000 1.00E+11 ? ALBA POLUX 80 - 2000 ~8000 1.00E+12 Many different monochromator types can be found E/DE is between 5000-10000 Flux on sample is 1011 ph/s or more

  6. Outline • Introduction • Optics of Diffraction gratings • Diffraction angles and efficiencies • Optics • 3.Monochromator design • A monochromator collection • DRAGON • SX700 • VLS • 4. Summary

  7. Outline • Introduction • Optics of Diffraction gratings • Diffraction angles and efficiencies • Optics • 3. Monochromator design • A monochromator collection • DRAGON • SX700 • VLS • 4. Summary

  8. m=1 m=0 b a m=-1 diffraction by reflection gratings The direction of diffracted rays is given by the period length The efficiency of the diffracted rays is given by the period profile

  9. diffraction by reflection gratings: direction grating equation a= 85º m = 2 m = 1 m = -1 3.5 m = 0 3 2.5 m = -2 1000 l/d0 2 b a 1.5 1 0.5 0 80 81 82 83 84 85 86 87 88 89 90 b(deg) Each wavelength is diffracted at several directions  Loss of flux Each direction has several wavelengths  Harmonic rejection

  10. diffraction of reflection gratings: efficiency Blazed Holographic - sinusoidal First order Optimized High Efficiency in blaze condition Less efficiency but wider l range Holographic Manufacturing  Fewer errors Varied Line Spacing Lamellar Multiple orders Even orders can be suppressed Ruling, lithographic, High Quality

  11. Lamellar 500 l/mm a=87º Blazed 500 l/mm a=87º Wavelength (nm) Wavelength (nm) Wavelength (nm) diffraction angle (deg) diffraction angle (deg) diffraction angle (deg) m = 1 12 m = 2 m = 0 10 8 m = -1 6 4 m = -2 2 0 80 81 82 83 84 85 86 87 88 89 90 diffraction of reflection gratings: efficiency The directions at which the photons are diffracted are determined by the period and the incidence angle, but the efficiency depends on the period profile Numerical calculations based no Electromagnetic Theory are needed for predictions on efficiency

  12. b a grating optics: focusing p q

  13. b b a a p q grating optics: focusing p q Gratings can be ruled on curved surfaces, then diffraction and focusing can be combined to reduce the number of elements in the monochromator Spheric surfaces at large incidence angles produce astigmatism and coma

  14. Outline • Introduction • Optics of Diffraction gratings • Diffraction angles and efficiencies • Optics • 3. Monochromator design • A monochromator collection • DRAGON • SX700 • VLS • 4. Summary

  15. grating monochromator Monochromatic beam source ‘white’ radiation grating exit slit focusing entrance slit focusing photon energy spot size Dispersion Spectral resolution Position in exit slit plane (L·b) Intensity Exit slit aperture Parts of a grating monochromator Resolution / flux is limited by: • Source size. • slit sizes. • dispersion rate. • diffraction limit. • Demagnification. • Aberrations (geometry changes). • Figure, alignment and slope errors. • efficiency, ruling errors.

  16. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake DRAGON Seya-Namioka Howells NOGARD Symmetrical NI Kunz SGM-VLS Flipper Wadsworth* SX700 *Not Rowland SX700+KB+ell Padmore SX700+KB+sph CLSX700 PGM-VLS

  17. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Seya-Namioka Symmetrical NI Wadsworth* *Not Rowland

  18. Seya-Namioka normal incidence monochromator R= 1m r,r’ = 0.818m • Photon energy scan (2-50eV) by simple rotation of the spherical grating • Scaled to minimize aberration on exit slita+b =70º15’ • Has astigmatism and coma • Does not provide a mechanism for harmonic rejection

  19. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (2-50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake Seya-Namioka Howells Symmetrical NI Kunz Flipper Wadsworth* *Not Rowland

  20. Obsolete grazing incidence monochromators Kunz Miyake entrance slit exit slit plane grating plane grating paraboloidal mirror spherical mirror plane mirror exit slit entrance slit Mechanics at UHV, figure error, defocus Coma limited, defocus, no h.h. rejection Paraboloidal mirror Howells entrance slit FLIPPER exit slit plane grating plane grating exit slit ellipsoidal mirror plane mirror entrance slit Paraboloidal mirror slope error, alignment Defocusing, figure error

  21. Howells Monochromator at Brookhaven NSLS (1979)

  22. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake DRAGON Seya-Namioka Howells NOGARD Symmetrical NI Kunz Flipper Wadsworth* *Not Rowland

  23. DRAGON SGM It was designed to avoid the figure errors and alignment errors that limit performance of monochromators. The recipe is: a) Using spherical surfaces only b) Reduce the number of moving parts c) Require stigmatic image only in dispersive direction d) Minimize coma by choosing grating radius - Compensate defocus by moving exit slit spherical mirror sphericalmirror source Entrance slit exit slit spherical grating • Exit slit has to move (2 motors for one parameter - l) • Fixed included angle (a+b)  no harmonic rejection, many gratings need to be used to cover a wide energy range

  24. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake DRAGON Seya-Namioka Howells NOGARD Symmetrical NI Kunz Flipper Wadsworth* SX700 *Not Rowland

  25. Fixed Focus Condition • Petersen (1980) Determines the focusing effect of plane gratings. Virtual Source r b a r0 Real Source The virtual source distance depends on the ratio between cosa and cosb

  26. Fixed Focus Condition • Petersen (1980) Determines the focusing effect of plane gratings. Virtual Source r b a r0 Real Source The virtual source distance depends on the ratio between cosa and cosb

  27. Petersen SX700 PGM Fixed Focus Condition plane grating Harmonic rejection Flux exit slit Fixed virtual source b a ellipsoidal mirror source plane mirror • Always focused on exit slit • Included angle must change  a plane pre-mirror is introduced • Virtual source position is fixed  • Fixed virtual source position is chosen to optimize … • Higher harmonic rejection • Blaze condition  Efficiency • There are 3 movements to control 1 degree of freedom  Complex • Astigmatic source  Horizontal virtual source ≠ Vertical virtual source curved spot on exit slit

  28. Mirror rotation axis Grating rotation axis R H 2b Zeiss scan mechanism (Reimer) For small deviation angles the mirror translation-rotation can be approximated by a single eccentric rotation R ~2b H ~R+b X0~L

  29. Zeiss scan mechanism (Reimer) For small deviation angles the mirror translation-rotation can be approximated by a single eccentric rotation Mirror rotation axis Grating rotation axis R R ~2b H ~R+b X0~L H 2b

  30. Jenoptik SX700 Slide from M.R. Howells

  31. ALS SX700 type monochromator

  32. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake DRAGON Seya-Namioka Howells NOGARD Symmetrical NI Kunz Flipper Wadsworth* SX700 *Not Rowland SX700+KB+ell SX700+KB+sph

  33. SX700 PGM: astigmatism correction plane grating exit slit Ellipsoidal cylinders KB source plane mirror Decoupling of horizontal and vertical focusing of virtual source in exit slit by means of a KB Nyholm:Elliptical cylinders (or for high demagnification, BM’s) Padmore: Spherical mirrors (or for small demagnification , ID’s)

  34. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake DRAGON Seya-Namioka Howells NOGARD Symmetrical NI Kunz Flipper Wadsworth* SX700 *Not Rowland SX700+KB+ell Padmore SX700+KB+sph

  35. Padmore monochromator Padmore determines the constant focal distance condition for spherical grating, so focusing on exit slit can be performed by a spherical grating.

  36. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake DRAGON Seya-Namioka Howells NOGARD Symmetrical NI Kunz Flipper Wadsworth* SX700 *Not Rowland SX700+KB+ell Padmore SX700+KB+sph CLSX700

  37. Collimated light SX700 plane grating toroidal mirror exit slit source cylindrical mirror plane mirror Use collimated light  Cff can be changed without changing refocusing optics Efficiency, Harmonic rejection or resolving power can be optimized Two Degrees of freedom (l,Cff) controlled by two movements

  38. 5 10 4 10 3 10 -1 0 1 10 10 10 Collimated light SX700 resolution limit focusing optics source focusing optics slit preoptics slit preoptics grating grating source Total Total Cff Source limited Slit limited where

  39. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake DRAGON Seya-Namioka Howells NOGARD Symmetrical NI Kunz SGM-VLS Flipper Wadsworth* SX700 *Not Rowland SX700+KB+ell Padmore SX700+KB+sph CLSX700 PGM-VLS

  40. Varied Line Spacing gratings + = Varied Line Spacing (VLS) gratings behave as reflective Fresnel lenses (diffractive lenses) They can compensate aberrations (such as meridional defocusing or coma)

  41. VLS grating monochromators VLS plane grating VLS-Padmore allows to remove post-focusing optics source plane mirror spherical mirror sphericalmirror source Entrance slit Fixed exit slit VLS DRAGON allows to keep the exit slit fixed 1 parameter - 1 motor VLS spherical grating

  42. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake DRAGON Seya-Namioka Howells NOGARD Symmetrical NI Kunz SGM-VLS Flipper Wadsworth* SX700 *Not Rowland SX700+KB+ell Padmore SX700+KB+sph CLSX700 PGM-VLS

  43. The monochromator collection PGM SGM or TGM Not Rowland Rowland Normal Incidence (< 50 eV) Grazing Incidence (50-2000 eV) Grasshopper Miyake DRAGON Seya-Namioka Howells NOGARD Symmetrical NI Kunz SGM-VLS Flipper Wadsworth* SX700 *Not Rowland SX700+KB+ell Padmore SX700+KB+sph CLSX700 PGM-VLS

  44. Summary Grazing Incidence diffraction grating monochromators are used for soft X-ray (100-2000 eV), and reach resolving power about 10.000, but efficiency is poorer than for crystals. There is a variety of diffraction grating monochromators that can perform well in terms of resolution and flux. The performance of monochromators is enhanced by… reducing aberration (defocus, coma) simplifying alignment requirements (use spheres when possible) reducing the number of coupled parameters DRAGON monochromator is very simple but a not so versatile SX700 is more versatile but not so simple Padmore monochromator is an intermediate case VLS gratings allow and aberration correction (incl. defocusing.)

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