Professor David Attwood
Lecture 1, Sept. 28, 2011

EUV and Soft X-Ray Optics
David Attwood
University of California, Berkeley

Cheiron SchoolSeptember 2011
SPring-8
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The short wavelength region of the electromagnetic
spectrumn = 1 – δ + iβ

δ, β << 1
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Lecture 1, Sept. 28, 2011

Available x-ray optical techniques

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Basic ionization and emission processes in isolatedatoms

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Energy levels, absorption edges, and characteristic line
emissions for a multi-electron atom

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Energy levels, quantum numbers, andallowed transitions for the copper atom

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Refractive index from theIR to x-ray spectral region

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Refractive index at nanometer wavelengths

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Refractive index in the soft x-ray
and EUV spectral region

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9Photoionization and electron binding energies

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Lecture 1, Sept. 28, 2011

Available x-ray optical techniques

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Diffractive and reflective optics for EUV,
soft x-rays and hard x-rays

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Diffractive optics for soft x-rays and EUV

Zone Plates

Gratings

PinholesCheironSchool_Sept2011_Lec1.ppt

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Diffraction from a transmission grating

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A Fresnel zone plate lensCheironSchool_Sept2011_Lec1.ppt

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A Fresnel zone plate lens used as a diffractive lens forpoint to point imaging

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Lecture 1, Sept. 28, 2011

Depth of focus and spectral bandwidth

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17A Fresnel zone plate lensfor soft x-ray microscopy

Courtesy of E. Anderson, LBNL
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189Professor David Attwood
Lecture 1, Sept. 28, 2011

Zone plates for ALS STXM beamlines –“3D Engineered Nanostructures”
Δr = 35 nm, Δt = 180 nm Au, N = 1700
D = 240 µm, 3 x 95 µmD central stop

Inner zones

Outerzone
close-upOuter zones

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The Nanowriter: high resolution electron beam
writing with high placement accuracy

Courtesy of E. Anderson (LBNL)
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Professor David Attwood
Lecture 1, Sept. 28, 2011

Zones plates for soft x-ray image formation

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New x-ray lenses: Improving contrast and resolution
for x-ray microscopy

C. Chang, A. Sakdinawat, P.J. Fischer, E.H. Anderson, D.T. Attwood, Opt. Lett. 2006; Sakdinawat and Liu, Opt. Lett. 2007;
Sakdinawat and Liu, Opt. Express 2008
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Diffraction limited x-ray imaging
Diffraction limited imaging is limited by the finitewavelength and acceptance aperture:
Δrresol. = k1 λ / NA

where NA = n sinθ and the constant k1 depends onillumination and specific image modulation criteria.
For x-rays
n = 1 – δ + iβ

δ, β << 1
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Diffraction limited x-ray imaging
For example, the widely accepted Rayleigh criteria for resolving twoadjacent, mutually incoherent, point sources of light, results in a 26%
intensity modulation.
λ = 2.48 nm(500 eV)Two overlappingAiry patterns

Δrresol. = 0.61 λ / NA

Note: Other definitions arepossible, depending on theapplication and the ability todiscern separated objects.

Resultant intensity pattern when
the two point sources are “justresolved”, such that the central
lobe maximum due to one point
source overlaps the firstminimum (dark ring) of the other.
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Resolution and illumination
Achievable resolution can be improved by varying illumination:An object pattern ofperiodicity d diffracts
light and is just capturedby the lens – setting
the diffraction limited
resolution limit.

Diffraction from an
object of smaller
periodicity, d/2, is justcaptured, and resolved,
when illuminatedfrom an angle.

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Resolution, illumination, and optical transfer function

Spatial frequency response of the optical system can be optimized by tailoring
the angular distribution of illumination.

σ=NAcond
NAobj(10.3)

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λ = 1.52 nm (815 eV)
Δr = 15 nm
N = 500
D = 30 µm
f = 300 µm
σ = 0.38
0.8 Δr = 12 nm

Cr/Si test pattern (Cr L3 @ 574 eV)(2000 X 2000,CheironSchool_Sept2011_Lec1.ppt
104 ph/pixel)

27

Hard x-ray imaging based on glancing incidence
reflective optics• Optics behave differently at these very short wavelengths(nanometers rather than 520 nm green light)• The refractive index is less than unity, n = 1 – δ + iβ
• Waves bend away form the normal at an interface• Absorption is significant in all materials and at all wavelength.
• Because of absorption, refractive lenses do not work, prisms donot, windows need to be extremely thin (100 nm or less).
• Because light is bent away from the surface normal, it possible tohave “total external reflection” at glancing incidence – a commonlyused technique.
• Kirkpatrick-Baez (KB)
mirror pair

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Professor David Attwood
Lecture 1, Sept. 28, 2011

Glancing incidence optics

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Total external reflection with finite β

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Professor David Attwood
Lecture 1, Sept. 28, 2011

Normal incidence reflection at an interface

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Focusing with curved glancing incidence optics

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Professor David Attwood
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Fluorescent microprobe based in crossedcylinders

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High resolution x-ray diffraction under high pressure using
multilayer coated focusing optics

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Lecture 1, Sept. 28, 2011

X-ray microprobe at SPring-8
Optical microscope
PIN photodiodemm
f1: 252mm

f2: 15098m
45m

SDDMirror manipulator

DCMUndulator

TC1SlitIon chamber

Beam monitor
Sample & Scanner

Incident Slit
Experimental hutch

2006

Front end

Courtesy of K. Yamauchi andH. Mimura, Osaka University.
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A high quality Mo/Si multilayer mirror
N = 40d = 6.7

Courtesy of Sasa
ˇ Bajt (LLNL)

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Cheiron School September 20113618Professor David Attwood
Lecture 1, Sept. 28, 2011

Scattering by density variations within a multilayer
coating

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Multilayer mirrors satisfy the Bragg condition

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Professor David Attwood
Lecture 1, Sept. 28, 2011

Multilayer mirrors satisfy the Bragg condition

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High reflectivity, thermally and environmentally robust multilayer
coatings for high throughput EUV lithography

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Atomic scattering factors for silicon (Z = 14)

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Atomic scattering factors for molybdenum (Z = 42)

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CXRO Web Site

X-Ray Interactions with Matter . Search CXRO

Facilities
Publications
Research
X-Ray Tools
Visitors
Personnel
Comments?
Server Stats. About CXRO

www.cxro.LBL.gov/• Atomic scattering factors• EUV/x-ray properties of the elements• Index of refraction for compound materials• Absorption, attenuation lengths, transmission• EUV/x-ray reflectivity(mirrors, thin films, multilayers)• Transmission grating efficiencies• Multilayer mirror achievements• Other
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Sputtered deposition of a multilayer coating

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Multilayer coatings – “1D nanostructures”
Eric Gullikson, Farhad Salmassi,
Yanwei Liu, Andy Aquila (grad),Franklin Dollar (UG)

World reference standard

Creating uniformity for
λ/50 optics

Wide band, narrow band,and chirped mirrors
for fsec applications

Reflectance (%)

20

Cr/Ti: 17%

Ti 2p

15

10CX050622B
Cr/Ti
θ=81.5 deg
d=1.384 nm
N=400
σ=0.35 nm

ReflectanceWorld record inwater window

50445

450455460

Photon energy (eV)CheironSchool_Sept2011_Lec1.ppt

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Recent progress in multilayer mirrors
Near-Normal Incidence Multilayer Mirrors
80

Sc CTiV

Peak reflectance (%)

7060

Si

H 2Owindow

50
403020Au

100110
Wavelength (nm)CheironSchool_Sept2011_Lec1.ppt

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Broad bandwidth mirrors
needed for as/fs pulses∆E(eV) ∙∆τ(fs) ≥ 1.8 fs∙eV (FWHM)• Multilayer mirrors depend on
constructive interference fromindividual interfaces• Higher reflectivity needs morelayers• Bandwidth gets narrower withmore layers
Attosecond pulse
 Broad bandwidth Limited number of layers

N<10 layers required for
200 as pulse (@13nm)

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Aperiodic multilayers for asec application
Optimizing multilayers for specificapplications requires the use ofsimulation of a multilayer stack withvariations in the thickness of eachmaterial in the multilayer.

δSuccessful design of aperiodic
multilayers requires:
1. EM wave in multilayer
structure
2. Optimization Algorithm
3. Sample preparation
4. Verification

A. L. Aquila, F. Salmassi, F. Dollar, Y. Liu, and E. Gullikson, "Developments in realistic design foraperiodic Mo/Si multilayer mirrors," Opt. Express 14, 10073-10078 (2006)
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Lecture 1, Sept. 28, 2011

The Cassegrain Telescope with multilayer coatings for
EUV imaging of the solar corona

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Multilayer Laue Lens for focusing hard x-rays

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Photon energy, wavelength, power

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Lectures online at www.youtube.com

Amazon.com

UC Berkeley
www.coe.berkeley.edu/AST/sxreuv
www.coe.berkeley.edu/AST/srms
www.coe.berkeley.edu/AST/sxr2009

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