X-ray sources and optics Dimosthenis Sokaras SLAC National - - PowerPoint PPT Presentation

X-ray sources and optics

Dimosthenis Sokaras SLAC National Accelerator Laboratory

Electromagnetic Waves Spectrum: X-rays

Energy → 0.1-100keV ¡ Wavelength → ¡

X-rays Interaction with Matter

Properties for the interaction of X-ray with matter are theoretically described with this Hamiltonian interaction absorption/ emission scattering

X-ray Sources: Motivation – Aim in Research

X-ray Sources: Principles for X-ray Emission Main Mechanisms for X-ray Sources Ø Characteristic X-rays

Ø Relaxation of atomic excited states

Ø Acceleration of charged particles

Ø Synchrotron Radiation Ø Bremsstrahlung Radiation Ø Plasma sources

Properties for an X-ray source

Performance Properties

• energy content
• flux
• Beam size
• angular convergence
• stability
• polarization
• time domain
• Coherence

Practical Properties

• Cost
• Availability/Access
• Portability ?

X-ray Sources: X-ray Tubes Characteristic X-rays based Sources: Ø Ionization of Primary Targets by means of irradiation:

Ø Heavy ions (Electrostatic Accelerators) Ø Electrons (X-ray Tubes, e- accelerators)

X-ray Sources: X-ray Tubes Characteristic X-rays based Sources: Ø X-ray Tubes Ø 1% of power becomes x-rays Ø Limitation = heat of the anode Ø Few W to several kW Ø Few to tens of keV photons Ø 4π emission

X-ray Sources: X-ray Tubes Characteristic X-rays based Sources: Ø X-ray Tubes

Ø Fixed anode tube Ø Rotating Anode Ø Liquid Metal Anode

X-ray Sources: X-ray Tubes Characteristic X-rays based Sources: Ø X-ray Tubes

Ø Fixed tube Ø Rotating Anode Ø Liquid Metal

Acta Cryst. (2013). D 69 , 1283–1288

X-ray Sources: Synchrotron Radiation Synchrotron Radiation based Sources: Ø Storage Rings

Ø Large Scale Laboratories Ø Relativistic Electrons/Positrons (1-7 GeV) Ø Acceleration Magnetic Field Ø Insertion Devices Ø Emission cone in forward angles

X-ray Sources: Synchrotron Radiation Synchrotron Radiation based Sources: Ø Storage Rings

Ø Bending Magnets (~1011 photons/s) Ø Wigglers (~1013 photons/s) Ø Undulators (~1014 photons/s)

Ø Properties

Ø Unprecedented flux Ø Very broad energy range Ø Forward emission / small divergence Ø Polarization

X-ray Sources: Synchrotron Radiation Synchrotron Radiation based Sources: Ø Storage Rings

Ø Bending Magnets (~1011 photons/s) Ø Wigglers (~1013 photons/s) Ø Undulators (~1014 photons/s)

Ø Properties

Ø Unprecedented flux Ø Broad Energy range Ø Forward emission Ø Polarization

1.0E+12 1.0E+13 1.0E+14 1.0E+15 1.0E+16 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 flux (cps/0.1% bp 1.0x0.2mrad or central cone) energy (eV) BL12 ¡ BL6 ¡ BL4 ¡ BL14 ¡ SSRL, T. Rabedeau

X-ray Sources: X-ray Free Electron Laser

Undulator Very long Undulator - XFEL Uncorrelated electron positions / radiated fields Microbunching by own radiated fields strongly correlated waves of electron and fields

X-ray Sources: X-ray Free Electron Laser Ø X-ray Free Electron Laser

Ø (~1025 photons/s)

X-ray Sources: Brilliance Quality Factor for X-ray Sources Brilliance = Radiated power per unit area per unit solid angle per unit spectral bandwidth Unit → photons/s/mrad2/mm2/0.1%bandwith

Brilliance → ¡ ¡Invariant quantity ¡

X-ray Sources: Brilliance

X-ray Sources: Natural Sources Natural X-ray Sources: Ø Radioisotopes (241Am, 55Fe, 109Cd, etc.) Ø Stars, Super Novas, Cosmic Background

An X-ray image of the Sun, T~2·106K

X-ray Sources: Motivation – Aim in Research

X-ray Optics: Delivering X-rays for Experiments

Transferring x-ray photons (beam) to the sample:

• focus size
• energy content
• angular convergence
• stability
• polarization

The job of x-ray optics is to transform the source beam characteristics to provide the best possible match to the sample requirements.

X-ray Optics: Principles X-rays Interaction Mechanisms for Optics:

Ø X-ray Diffraction ( monochromatizing x-rays) Ø X-ray Refraction/Reflection (guiding/collimating)

X-ray Optics: Refractive Index

Refractive index

phase term attenuation term

X-ray Optics: Refraction

Snell Law:

n<1

Refraction

X-ray Optics: Total External Reflection

Total external reflection δ ~ 10-5-10-6 θc< 3o-4o

X-ray Optics: X-ray Mirrors

Focusing

condense beam to source dimensions on sample demagnify source image to better couple photons on small sample at the expense of greater angular convergence

• n sample)

Collimation

collimate divergent beam to improve energy resolution of a monochromator

Power filter

absorb waste power at low power density on grazing incident optic

Harmonic filter

suppress higher energy contamination of beam (low pass filter)

X-ray Optics: X-ray Mirrors

Focusing

condense beam to source dimensions on sample demagnify source image to better couple photons on small sample at the expense of greater angular convergence

• n sample)

Collimation

collimate divergent beam to improve energy resolution of a monochromator

Power filter

absorb waste power at low power density on grazing incident optic

Harmonic filter

suppress higher energy contamination of beam (low pass filter)

X-ray Optics: X-ray Mirrors

Focusing

condense beam to source dimensions on sample demagnify source image to better couple photons on small sample at the expense of greater angular convergence

• n sample)

Collimation

collimate divergent beam to improve energy resolution of a monochromator

Power filter

absorb waste power at low power density on grazing incident optic

Harmonic filter

suppress higher energy contamination of beam (low pass filter)

X-ray Optics: X-ray Mirrors

Focusing

condense beam to source dimensions on sample demagnify source image to better couple photons on small sample at the expense of greater angular convergence

• n sample)

Collimation

collimate divergent beam to improve energy resolution of a monochromator

Power filter

absorb waste power at low power density on grazing incident optic

Harmonic filter

suppress higher energy contamination of beam (low pass filter)

X-ray Optics: X-ray Mirrors

Focusing

condense beam to source dimensions on sample demagnify source image to better couple photons on small sample at the expense of greater angular convergence

• n sample)

Collimation

collimate divergent beam to improve energy resolution of a monochromator

Power filter

absorb waste power at low power density on grazing incident optic

Harmonic filter

suppress higher energy contamination of beam (low pass filter)

X-ray Optics: X-ray Mirrors

Focusing

condense beam to source dimensions on sample demagnify source image to better couple photons on small sample at the expense of greater angular convergence

• n sample)

Collimation

collimate divergent beam to improve energy resolution of a monochromator

Power filter

absorb waste power at low power density on grazing incident optic

Harmonic filter

suppress higher energy contamination of beam (low pass filter)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 5 10 15 20 25 30 35 40

energy (keV) reflectivity

Si Rh Pt 2.7mrad alpha

X-ray Optics: X-ray Diffraction

Bragg Diffraction: Constructive interference of radiation reflections from sequential planes. ) sin( = θ d λ m 2

X-ray Optics: X-ray Diffraction

• Diffraction Gratings
• Bragg-type x-ray crystal optics

soft x-rays hard x-rays

2dhkl sin θ = λ mλ d = (sin α + sin β)

X-ray Optics: X-ray Diffraction - Darwin Width

• Energy Resolution- Darwin width (dynamical diffraction

theory) and geometrical factors

• Darwin width curves

2d sin θ = λ λ ∆λ = tan θ ∆θ

(arcsec)

kin

• 100
• 50

50 100 150 200

reflectivity

0.2 0.4 0.6 0.8 1

Darwin width for Si(440) @ 88 deg

65meV @ 6462eV

X-ray Optics: Double Crystal monochromators

Liquid Nitrogen Cooled Monochromators cooling channel bundle

X-ray Optics: Double Crystal Monochromators - Dupond and Acceptance Diagram

12380 12400 12420 12440 12460 12480 12500 14.98 15 15.02 15.04 15.06 15.08 15.1 15.12 angle energy

• T. Rabedeau, SSRL

X-ray Optics: Double Crystal Monochromators - Dupond and Acceptance Diagram

12380 12400 12420 12440 12460 12480 12500 14.98 15 15.02 15.04 15.06 15.08 15.1 15.12 angle energy

Darwin

• T. Rabedeau, SSRL

X-ray Optics: Double Crystal Monochromators - Dupond and Acceptance Diagram

12380 12400 12420 12440 12460 12480 12500 14.98 15 15.02 15.04 15.06 15.08 15.1 15.12 angle energy

Darwin

• T. Rabedeau, SSRL

X-ray Optics: Double Crystal Monochromators - Dupond and Acceptance Diagram

12380 12400 12420 12440 12460 12480 12500 14.98 15 15.02 15.04 15.06 15.08 15.1 15.12 angle energy

beam convergence/divergence

• T. Rabedeau, SSRL

X-ray Optics: Double Crystal Monochromators - Dupond and Acceptance Diagram

12380 12400 12420 12440 12460 12480 12500 14.98 15 15.02 15.04 15.06 15.08 15.1 15.12 angle energy

Darwin beam convergence/divergence energy resolution:

• Darwin = 32.4
• total = 64.7
• T. Rabedeau, SSRL

X-ray Optics: Monochromatizing Divergent Sources

Ø Based on Bragg Diffraction Ø Monochromator & Focusing Curved vs. Plate Crystal Ø Increased beam area that meets Bragg condition. Ø Improve Energy resolution Ø Focusing Effect

Rowland circle

Doubly Curved Crystals

X-ray Optics: Monochromatizing Divergent Sources

X-ray Optics: X-rays transmission in waveguides

Analytical description of waveguide Angle of incidence at point Α(x,y,z) Angle of incidence at Geometrical Parameters constrain

X-ray Optics: X-rays transmission in waveguides

Reflectivity

Photon energy: 8 keV

X-ray Optics: Polycapillary X-ray lenses

Bundles of thousands glass mono-capillaries in certain arrangements can be used for: Ø Directing Ø Focusing Ø Parallelizing

X-ray Optics: Polycapillary X-ray lenses

X-ray Optics: Polycapillary X-ray lenses

Polycapillary lens Functionality: Spot focusing of diverging x-ray beam. Main Applications: Focusing x-ray tubes beams .

d1, d2 0.3…1 mm dmax 1…2 mm l ¡ 40…50 mm f1,f2 ¡ 15…100 mm FWHM 15…100 µm ¡

X-ray Optics: Polycapillary-based XRF

X-ray tube

detector sample polycapillary

X-ray tube based Micro-XRF setup

Summary X-ray Sources

X-ray Tubes

Synchrotron Radiation Beamlines

X-ray Optics

Mirrors

Monochromators Double Curved Crystals Polycapillary lenses

Thank you !