X- X- -ray optics -ray optics ray optics ray optics Crystal optics Crystal optics Crystal optics Crystal optics Jürgen Härtwig Jürgen Härtwig Jürgen Härtwig Jürgen Härtwig ESRF X-ray Optics Group, Crystal Laboratory ESRF X-ray Optics Group, Crystal Laboratory X O O G O G O G O O X X G G G X X X ESRF X- X X- X -ray Optics Group -ray Optics Group ray Optics Group ray Optics Group
What was already presented (among others) ? Physics of the electron beam source (Boaz Nash) Physics of X-ray radiation production and transport (Manuel Ph i f X di ti d ti d t t (M l Sánchez del Río) Multilayers in synchrotron optics (Christian Morawe) Energy resolving detectors for X-ray spectroscopy (John Morse) So we continue today with the X-ray optics So we continue today with the X ray optics
Outline Outline 1. Introduction 2. Monochromators 3. Some properties of asymmetrical reflections 3 S ti f t i l fl ti 4. Shortly about high energy resolution 5. Crystal quality and how to measure it (6 Plane or divergent monochromatic or (6. Plane or divergent, monochromatic or polychromatic waves in our experiments?)
1. Introduction 1. Introduction 1. Introduction 1. Introduction Some questions I plan to discuss and maybe to answer: Which kind of monochromators are used? How may I change the energy resolution, beam divergence, beam dimension? l ti b di b di i ? May the Bragg diffraction geometry have an influence on the coherence? Role of source size and angular source size. Influence on transversal R l f i d l i I fl t l coherence, resolution etc. ? Are “Imaging quality” “focusing properties” “coherence preservation” Are Imaging quality , focusing properties , coherence preservation related? What is a “highly perfect” crystal? What are the lowest strains that we can measure? Is there a “highly parallel (monochromatic)” beam? Is there a “nanometric parallel” beam? parallel beam? We need to define what a “plane” or a “monochromatic” wave could be in the real experimental life. How may we approximate them? p y pp etc.
Optical system / experimental set-up: Optical system / experimental set up: Source optical elements sample optical elements detector The task of the optics: To transform the beam to obtain the best matching with the o transform the beam to obta n the best match ng w th the experiment; not loosing the good properties of the beam after its creation. It acts on: - shape shape - wavelength/energy - divergence - polarisation - coherence
“No optics is the best optics”!? Y Yes, but … b t In principle possible - all in vacuum, working with non-modified “white” or “pink” beam. However, not very useful. We may need e.g. monochromatisation, focussing, ... .
A whole zoo of optical elements • slits, pinholes • filters, windows • mirrors (reflectivity based) • beam splitter monochromators (crystals) • monochromators/collimators/analysers (crystals, h / ll / l ( l multi-layers – often also called “mirrors”) • phase plates (phase retarder, polarizer) (crystals) h l ( h d l i ) ( l ) • lenses, zone plates • combined elements (ML gratings, Bragg-Fresnel-lenses) bi d l t (ML ti B F l l ) • etc. Mirrors and monochromators, collimators, analysers flat, but also bent for collimation, focussing, image f at, ut a so nt for co mat on, focuss ng, mag magnification, ...
Main physical effects used in X-ray optics were discovered in the first years starting from the discovery of X-rays by the first years starting from the discovery of X rays by C. W. Röntgen: absorption (Röntgen 1895/96 filters) absorption (Röntgen 1895/96 filters) Bragg-diffraction (Laue 1912 monochromators, etc.) specular reflection (Compton 1922 mirrors) refraction (Larsson, Siegbahn, Waller 1924 later lenses) Properties of double and many-crystal set-ups: P ti f d bl d t l t Jesse W. M. DuMond, Physical Review, 52 , 872-885 (1937) DuMond graphs dispersive and non dispersive set ups DuMond graphs, dispersive and non-dispersive set-ups, channel cut crystals (later invented as “Bonse-Hart-camera”), four crystal spectrometer (later invented as “Barthels four crystal spectrometer (later invented as Barthels monochromator”), etc. B But - many newer developments d l
Quite a lot of literature Q Overviews: Tadashi Matsushita, X-ray Monochromators , in Handbook on Synchrotron Radiation, Vol. 1, ed. E. E. Koch, North-Holland P bli hi Publishing Company, 1983 C 1983 Dennis M. Mills, X-Ray Optics for Third-Generation Synchrotron Radiation Sources , in Third-Generation Hard X-ray Sources, ed. Dennis M. Mills, John Wiley & Sons Inc., New York, 2002 ,
Short remark concerning beam dimensions Short remark concerning beam dimensions Short remark concerning beam dimensions Short remark concerning beam dimensions Few years ago – micro-beams were modern, now – nano-beams are in vogue now nano beams are in vogue. But - we need all kind of beams: large beams (decimetre sized) g ( ) and small ones (nanometre sized), “parallel” divergent and focussed beams parallel , divergent and focussed beams.
Beam dimensions – example: paleontology p p gy Examples from Paul Tafforeau
Nearly 4 orders of magnitude in dimension Without scanning Without magnification Without magnification Multi scale experiments!
Further large scale objects: the monochromator crystals For their tests we like to use: wide beams if possible at least 10 x 45 mm 2 (V x H) wide beams, if possible at least 10 x 45 mm 2 (V x H), with a “good” spatial resolution ~ 1 μ m The above field of view and resolution needs sensors with: 10,000 x 45,000 pixels, this is 450 Mega pixels Not yet on the market (?) Not yet on the market (?)
2. Monochromators 2. Monochromators but also by: filters + source spectrum + 10 0 10 0 scintillator screen response spectrum E = 8 keV E = 8 keV (P (Paul Tafforeau/ID19) l T ff /ID19) 10 -1 10 -1 forbidden area forbidden area 10 -2 10 -2 10 -2 10 -2 d reflectivity d reflectivity R = 1 R = 1 ors) ors) 10 -3 10 -3 10 10 (Mirro (Mirro Integrated Integrated d ML's d ML's n ML's n ML's High-Z High-Z Ge 111 Ge 111 10 -4 10 -4 Low-Z Low-Z epth-graded epth-graded Si 111 Si 111 h-resolution h-resolution ML's ML's C * 111 10 -5 10 -5 Crystals Crystals high high de de Be 110 Be 110 10 -6 10 -6 10 -6 10 -6 10 -5 10 -5 10 -4 10 -4 10 -3 10 -3 10 -2 10 -2 10 -1 10 -1 10 0 10 0 E/E High resolution Ch. Morawe 10 -8 and below
Bragg diffracting X-ray optical elements like gg g y p monochromators, analysers, etc. Manufactured from dislocation free crystals. M f t d f di l ti f t l Mostly used: Si, Ge, C* (locally dislocation free diamond) . We mainly use silicon. They must be tailored into monochromators etc. Orientation cutting lapping polishing and etching Orientation, cutting, lapping, polishing and etching. Strain free crystal preparation. Accurate and stable mounting. Adequate cooling scheme Adequate cooling scheme.
Crystal laboratory: Crystal laboratory: Manufacturing of nearly all perfect Si (and few Ge) crystal Si (and few Ge) crystal monochromators & analysers, etc for all ESRF beam lines, CRG beamlines and external b li d t l laboratories. Silicon pieces are made from float Silicon pieces are made from float zone silicon ingots with 100 mm diameter (Wacker). More than 1.5 tons of silicon single crystal material has been processed in more than twenty years in more than twenty years. Example manufacturing crystal monochromators and analysers monochromators and analysers
Which types of monochromators are used? yp
Single crystal monochromators - beam splitter monochromators white beam white beam white beam monochr. beam 2 monochr. beam 1 Double crystal monochromators monochr. beam Reflection (Bragg) and white beam t transmission (Laue) nsmissi n (L ) geometry used
Single crystal monochromators - beam splitter monochromators white beam white beam white beam monochr. beam 2 monochr. beam 1 Double crystal monochromators Reflection (Bragg) and monochr. beam white beam t transmission (Laue) nsmissi n (L ) geometry used
Few theory and definitions Few theory and definitions Reflectivity (and transmissivity) curve of a crystal plane plane R R Theory monochromatic wave Plane & monochromatic Darwin incoming wave, incoming wave, width width varying the angle of incidence counting the diffracted photons R T A 1 R+T+A=1 Real situation - experiment Rocking curve Convolution (autocorrelation) of reflectivity (or transmissivity) curve any wave with other reflectivity curves, or/and wavelength (energy) g ( gy) distribution, or/and divergence distribution ( instruments/apparatus function) ( pp f )
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