Optical Component for Synchrotron Light School on Synchrotron and Free-Electron-Laser Methods for Multidisciplinary Applications ICTP, 7 th May -18 th May 2018 1 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical components for SL: mirrors and monochromators low emittance electrons beam produces a high brilliance x-ray photons beam. “ ...The finite quality and the fundamental limits of the optical components increase the emittance of the beam …… . The main aim of the optical design consists on minimizing the inevitable beam degradation … ” Jean Susini “ Design parameters for hard x-ray mirrors: the ESRF case ” detectors OPTICAL ENGINEERING/February 1995/Vol. 34 2/361 monochromators The most important optical elements for sources mirrors a beamline: slits filters • mirrors • monochromators 2 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical components for SL Mirrors: total reflection If we consider θ as the angle between the incoming radiation and the mirror surface (grazing angle), the x-ray beam will be totally reflected when θ < θ c For x – rays the refraction index is n = 1- δ where 0 < δ < 1, and therefore 0 < n < 1 θ > θ c θ = θ c θ < θ c 3 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical components for SL Mirrors: total reflection θ c = 1.66 λ [A]( ρ ) 1/2 [g/cm 3 ] 1.0 Grazing angles 0.8 Angoli di radenza 0.185 0.6 0.180 Reflectivity 0.175 0.170 0.150 0.4 Curve di riflettività in funzione dell'energia al variare dell'angolo di radenza 0.2 Materiale del coating : Platino 0.0 3 2 4 6 8 10 12 14 16 18 20 22 24 26 30x10 energy [eV] Reflectivity as function of the photons energy and the grazing angle in degrees Mirror coating: Platinum 4 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical components for SL Mirrors: focusing Ellipsoidal surface Best approximation circle ρ tangential = 2 f / sin ϑ an ideal focusing mirror will focus a point source Tangential focusing into another point according to the formula 1/q+1/p=1/f ρ sagittal = 2 f sin ϑ Sagittal focusing § Bendin magnet § Extended source (wiggler and undulators) 5 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical Metrology Lab Laser beam Linear array detector Reference Surface under test Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
200 Shape difference (mm) Shape difference (mm) 0 Effect of 100V at: 00 01 02 03 -200 04 05 06 07 08 09 10 11 12 13 -6 -400x10 0 200 400 600 800 mirror position (mm) 13 active mirror sections 100 Residual height (mm) 10 minutes / measurement Resdual hegiht (mm) 0 Total time > 130 minutes -100 on 860 mm -200 all @200V 555 nm P-V 153 nm rms 1st correction 155 nm P-V 34 nm rms 2nd correction 112 nm P-V 25 nm rms -300x10 -6 voltage stability 0 200 400 600 800 mirror position (mm) Optical Metrology Lab Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
In last 10 years • 200 - 400 mm long flat mirrors: from ~ 1 µrad to ~ 0.2 µrad rms Ion beam figuring (IBF) now almost normally applied • curved mirrors R=100 m , 100 mm long : 0.45 µrad rms Toroid R=300 m, r = 100 mm, 200mm long : 0.5 µrad rms • High quality ellipses IBF finished, 200mm long: 0.8/1 µrad rms from best ellipse F=900mm / 500mm @ 2.5 / 2 deg Fluid jet polishing ,100 mm long: 0.07 µrad rms from best ellipse F=180 mm / 280mm @ 2.5/ 3 mrad Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Goals for the next 10 years Mirror shape errors Slope errors < 50 nrad rms from best shape : flat and moderate curvature height errors < 0.1 nm rms Improvement of figuring technology Convergence of iterative figuring process Development of fast accurate metrology procedures At synchrotrons At manufacturers Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical components for SL Mirrors: figure errors modification b a K-B optical system holder α 1,2 =2 � � ��� ������ a 1,2 = 98754 - 99354 mm b 1,2 = 1750 - 1200 mm pitch End-stations need roll hig flux - great demagnification - small focal spot K-B system advantages M1 M2 § Decoupling vertical and horizontal beam components § It is hard to realize thick ellipsoidal mirrors with this demanding demagnification focus K-B bendable system advantages FEL § Focusing of the 2 sources at different distance with the same couple of mirrors Horizontal mirror M1 M2 § Possibility to change the focal plane position § Improvement of the coherent beam wavefront Vertical mirror K-B active optical system – DiProI L. Raimondi et all. Status of the K-B bendable optics at FERMI@Elettra FEL Proc. Of SPIE Vol.9208 920804-1 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
§ KAOS PMMA indentation / WFS measurement Focal spot simulations from metrology PMMA ablation imprint Reconstruction from Hartmann WFS data https://en.wikipedia.org/wiki/Shack–Hartmann_wavefront_sensor WFS reconstruction at 32 nm: FWHM = 5.7x6.5 µ m 2 Optical microscope 100X Good agreement between in-house reconstruction, PMMA, simulations (WISE, SRW) Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
§ KAOS PMMA indentation / WFS measurement Focal spot simulations from metrology PMMA ablation imprint Profilometry at best Simulations curvature (LTP) (WISE, SRW) Optical microscope 100X Good agreement between in-house reconstruction, PMMA, simulations (WISE, SRW) Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical component for SL: Visible light monochromators Dispersion of radiation through the matter: the RIFRACTION Visible radiation optical PRISM The glass refraction index depends on the radiation wavelength, the optical prism splits the visible radiation as function of the energy We can sample the dispersed beam with a slit selecting part of it. The spectral resolution will depend on the glass refraction index n, on the slit aperture and on the distance between slits and the optical prism. 13 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical component for SL: Soft x-rays monochromators Dispersion of radiation from a periodic structured surface: the surface DIFFRACTION GRATINGS Soft Hard Microwave I.R. Visible U.V. X-ray X-ray Ordini interni (+) β Ordine zero α Ordini esterni (-) n λ sin ( ) sin ( ) = α − β d d The optical surface is machined with particular periodic structures that are origin of interference phenomena with the incoming radiation 14 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical component for SL: Hard x-rays monochromators Dispersion of radiation from a bulk periodic atomic structure: The bulk DIFFRACTION Single crystal The Bragg’s law Microwave Hard Soft The radiation penetrates the I.R. Visible U.V. X-ray X-ray material and is diffused by the atoms of the structure. The diffused waves interfere. The interference will be constructive if the difference in optical path will be a multiple of the wavelength λ : 15 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical component for SL: monochromators 2 d sin ϑ = n λ From the Bragg’s law � therefor sin ϑ = 1 ⇒ λ max and the Bragg angle is 90o λ max = 2d 16 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
� Optical component for SL: monochromators � from the derivative of the Bragg’s low an important property of the hard x-ray monochromators energy resolution = Δ E Δ λ ( ) = Δ ϑ cot g ϑ B E λ Δθ is the convolution of two contributes: Δθ Δθ beam - angular divergence of the radiation beam in the scattering plane ω s - the intrinsic angular bandwidth of the crystal monochromator known as Darwin width 17 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
Optical component for SL: monochromators Case with Δθ Δθ beam >> ω s white beam with divergence in the plane of scattering θ min / E max The crystal will diffract all the rays with: θ min ≤ θ Β ≤ θ max θ max / E min In this case the energy bandwidth is Δ E ≈ Δθ beam cotg( θ B ) E monochromator E max E min 18 Edoardo Busetto & Luca Rebuffi - MVO Group ICTP, Grignano (TS), 07/05/2018 Elettra - Sincrotrone Trieste S.C.p.A.
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