Extreme Ultraviolet Polarimetry with LaserGenerated High-Order Harmonics
N. BRIMHALL, N. HEILMANN, N. HERRICK, D. D.
ALLRED, R. S. TURLEY, M. WARE, J. PEATROSS
Brigham Young University, Provo, UT 84602
Overview and Conclusions

We have constructed an extreme ultraviolet (EUV) polarimeter
that employs laser-generated high-order harmonics as the
light source.

This instrument represents a potential ‘in-house’ instrument
at facilities developing EUV thin films (as opposed to
synchrotron).

We have compared reflectance data with that taken at the
Advanced Light Source (ALS) and with calculated data. These
measurements agree well.

In addition to absolute reflectance, we can extract all desired
information out of relative measurements of p- and spolarized reflectance, reducing systematic errors.
Introduction: Extreme Ultraviolet Optics
and Optical Constants
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Two examples
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IMAGE satellite 2000
(above)
ThO2 optical constants
(right)

Optical constants in the EUV are typically
unknown, incomplete, or inaccurate.

This is important for those designing EUV
optics for applications such as
astronomy, lithography, or microscopy.
Optical Constants


Optical constants are typically determined by
measuring reflectance as a function of angle.
Reflectance is then fitted to the Fresnel equations
to find the optical constants.
EUV light
incident angle (Θ)
sample
Sources of EUV light

Synchrotron source
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

Plasma source


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
High flux
Wide, continuous wavelength range
Not local, expensive to run, large footprint
‘Fixed’ polarization
Low flux
Wide wavelength range only a few
wavelengths in the range
Local
Unpolarized
High Harmonics

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Fairly high flux
Wide wavelength range, good spacing of
wavelengths throughout the range.
Local
Easily rotatable linear polarization
High Harmonic Generation
EUV Grating
EUV Generation
EUV Light
800 nm,
35 fs, 10 mJ
Laser Pulses
MCP
Detector
Gas (He, Ne, Ar)

Fairly high flux (6x108 photons/sec at a
spectral resolution of 180)

Wide wavelength range with good spacing
of wavelengths within the range (8-62 nm)

Easily rotatable linear polarization
λ = 800 nm / q

Small footprint, low cost of operation
Orders 37 to 77
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Potential ‘in-house’ instrument at facilities
developing EUV thin films
Wavelengths of 10 nm-22 nm
Instrument Overview

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Easily rotatable linear polarization
Ability to measure reflectance of multiple wavelengths simultaneously
Extensive scanning ability
Reflectance Measurements
Ratio Method

Noise (especially systematic noise) is a problem for
retrieving accurate optical constants

A measurement of p- to s-polarized reflectance
reduces systematic noise significantly
Can we extract the same information?
Yes!
Future Work

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One step away from an ellipsometer.
Can we measure phase information?
This is difficult in the EUV because there are no
good polarizers
Diffraction pattern
depends on the phase
difference between the
reflection from the two
materials
“Unknown” material
“Known” material
Conclusions

We have constructed a new instrument that uses high-order
harmonics to measure optical properties of materials in the
EUV.

Our compact source has a wide wavelength range, high flux,
and easily rotatable linear polarization.

We have compared reflectance measurements with those
taken at the ALS and computed data. These measurements
agree.

We can reduce systematic noise by measuring the ratio of ppolarized to s-polarized reflectance, and we can extract the
same information from this as from absolute reflectance.
Acknowledgements
We would like to recognize NSF grant PHY0457316 and Brigham Young University for
supporting this project.