Extreme Ultraviolet Polarimetry with Laser-Generated High-Order Harmonics
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Extreme Ultraviolet Polarimetry with Laser-Generated 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
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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 s-polarized reflectance, reducing systematic errors.
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Introduction: Extreme Ultraviolet Introduction: Extreme Ultraviolet Optics and Optical ConstantsOptics and Optical Constants
Two examples 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.
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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.
sample
incident angle (Θ)
EUV light
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Sources of EUV light Synchrotron source
High flux Wide, continuous wavelength range Not local, expensive to run, large
footprint ‘Fixed’ polarization
Plasma source Low flux Wide wavelength range only a few
wavelengths in the range Local Unpolarized
High Harmonics Fairly high flux Wide wavelength range, good spacing
of wavelengths throughout the range. Local Easily rotatable linear polarization
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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
Small footprint, low cost of operation
Potential ‘in-house’ instrument at facilities developing EUV thin films
800 nm, 35 fs, 10 mJ Laser Pulses
Gas (He, Ne, Ar)
EUV Grating
MCP Detector
EUV GenerationEUV Light
λ = 800 nm / q
Orders 37 to 77
Wavelengths of 10 nm-22 nm
High Harmonic Generation
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Instrument Overview
Easily rotatable linear polarization Ability to measure reflectance of multiple wavelengths simultaneously Extensive scanning ability
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Reflectance Measurements
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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
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Can we extract the same information?
Yes!
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Future Work
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
“Known” material
“Unknown” material
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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 p-polarized to s-polarized reflectance, and we can extract the same information from this as from absolute reflectance.
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Acknowledgements
We would like to recognize NSF grant PHY-0457316 and Brigham Young University for supporting this project.