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Extreme Ultraviolet Polarimetry Utilizing High-Order Harmonics

Extreme Ultraviolet Polarimetry Utilizing High-Order Harmonics. Nicholas Herrick, Nicole Brimhall, Justin Peatross Brigham Young University. Outline. Introduction to extreme ultraviolet (EUV) optics Finding optical constants BYU Polarimeter High-intensity laser source

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Extreme Ultraviolet Polarimetry Utilizing High-Order Harmonics

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  1. Extreme Ultraviolet Polarimetry Utilizing High-Order Harmonics Nicholas Herrick, Nicole Brimhall, Justin Peatross Brigham Young University

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

  3. Extreme Ultraviolet (EUV) 121 nm - 10 nm

  4. 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 Earth’s Plasmasphere at 30.4 nm. NASA’s IMAGE extreme ultraviolet imager

  5. Finding Optical Constants • Reflectance as a function of • Angle • Polarization • Wavelength

  6. Finding Optical Constants • Reflectance as a function of • Angle • Polarization • Wavelength

  7. BYU Polarimetry - High-intensity laser • The BYU polarimeter is a combination of three optical systems: - High harmonic generator - Polarimeter

  8. High-intensity Laser Source • 800 nm, 30 x 10-15 sec pulse width

  9. 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

  10. BYU EUV Polarimeter • Simultaneous measurements at multiple wavelengths • Useable angles 0 ° - 40° from grazing • Easily adjustable linear polarization

  11. BYU EUV Polarimeter

  12. 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

  13. 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

  14. 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

  15. 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

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

  17. Polarimetry Results

  18. 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.

  19. 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

  20. Future Research • EUV H2O Transmission

  21. 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?

  22. 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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