Extreme Ultraviolet Polarimetry Utilizing High-Order Harmonics

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Extreme Ultraviolet Polarimetry Utilizing
High-Order Harmonics

• Nicholas Herrick, Nicole Brimhall, Justin
  Peatross
• Brigham Young University

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Outline

• Introduction to extreme ultraviolet (EUV) optics
• Finding optical constants
• BYU Polarimeter
• High-intensity laser source
• High harmonic generation
• Polarimeter
• Controllable harmonic attenuation
• Results

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Extreme Ultraviolet (EUV)

• 121 nm - 10 nm

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Why Study EUV Optical Constants?

• Optical constants in the EUV range are largely
  unknown or poorly characterized.
• Because of this, designing EUV optics is
  difficult.
• Applications of EUV light
• computer chip lithography
• microscopy
• astronomy

Earths Plasmasphere at 30.4 nm. NASAs IMAGE
extreme ultraviolet imager
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Finding Optical Constants

• Reflectance as a function of
• Angle
• Polarization
• Wavelength

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Finding Optical Constants

• Reflectance as a function of
• Angle
• Polarization
• Wavelength

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BYU Polarimetry

• The BYU polarimeter is a combination of three
  optical systems

- High-intensity laser
- High harmonic generator
- Polarimeter
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High-intensity Laser Source

• 800 nm, 30 x 10-15 sec pulse width

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High Harmonic Generation

• A high intensity laser is focused into a cell
  containing helium or neon.
• Resultant EUV light ranges from 8 - 62 nm.
• Changes in laser linear polarization transfer to
  resultant EUV polarization

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BYU EUV Polarimeter

• Simultaneous measurements at multiple
  wavelengths
• Useable angles 0 - 40 from grazing
• Easily adjustable linear polarization

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BYU EUV Polarimeter
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EUV Controllable Attenuation

• By adjusting the voltage of the MCP, we can
  detect over the entire range of reflectance
• This is introduces and un-characterizable
  variable and is unacceptable

• The dynamic range of our micro-channel plate
  detector is insufficient to perform reflectance
  measurements over the entire range of our
  instrument.

Effective MCP dynamic range
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EUV Controllable Attenuation

• Attenuation via secondary gas cell
• 14 cm long secondary gas cell is located
  downstream from the primary harmonic generation
  cell
• Neon is added to the cell at pressures from 0 - 2
  torr
• Reduction of EUV flux during incident
  measurements increases the dynamic range of our
  detector
• Using the absorption coefficient of neon the flux
  is corrected

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EUV Controllable Attenuation

• EUV light runs the full length of the secondary
  gas cell.
• Differential pumping chamber allows venting into
  harmonic generation chamber.

Attenuator in harmonic generation chamber
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EUV Controllable Attenuation

• Adjusting secondary gas cell pressure attenuates
  flux so that it falls within the dynamic range of
  the MCP

Pressure 1
Pressure 2
Pressure 3
Effective MCP dynamic range
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Polarimetry Results

• Reflective measurements as low as 0.2
• Easily changeable linear polarization
• Wavelength range 8-62 nm

• High EUV flux (6 x 108 photons/sec at 100 eV)
• Positioning system accurate to 0.3 mm

Harmonics averaged in the y-direction.Data taken
at 10º from incidence.
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Polarimetry Results
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Summary

• We have constructed an EUV polarimeter utilizing
  high-order harmonics as the light source.
• The harmonic source has been shown to provide
  ample flux for reflectance measurements through
  50º from grazing.
• Polarimeter reflectance data matches those taken
  at the Advanced Light Source.
• Characterization and use of the secondary gas
  cell provides the necessary dynamic range for
  reflectance measurements.

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Future Research

• EUV H2O Transmission
• Direct characterization of H2O transmission
  constants utilizing the secondary gas cell

CXRO Website
http//henke.lbl.gov/optical_constants/intro.html
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Future Research

• EUV H2O Transmission

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Future Research

• EUV H2O Transmission
• Two steps
• Hydrogen and Oxygen transmission constants
  verification
• Water vapor transmission characterization
• Comparison with CXRO data
• Further work in optical constants
• Examination of additional oxidized multilayer
  mirrors
• Other Experiments?

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Acknowledgements

• Principle contributors
• Dr. Justin Peatross
• Nicole Brimhall
• Dr. David Allred
• The National Science Foundation
• The College of Physical and Mathematical
  Sciences, BYU

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