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 High harmonic generation Polarimeter Controllable harmonic attenuation Results

Extreme Ultraviolet (EUV) 121 nm - 10 nm

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

Reflectance as a function of –Angle –Polarization –Wavelength Finding Optical Constants

Reflectance as a function of –Angle –Polarization –Wavelength Finding Optical Constants

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

High-intensity Laser Source 800 nm, 30 x sec pulse width

High Harmonic Generation A high intensity laser is focused into a cell containing helium or neon. Resultant EUV light ranges from nm. Changes in laser linear polarization transfer to resultant EUV polarization

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

BYU EUV Polarimeter

EUV Controllable Attenuation 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 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

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 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

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

EUV Controllable Attenuation Adjusting secondary gas cell pressure attenuates flux so that it falls within the dynamic range of the MCP Effective MCP dynamic range Pressure 1 Pressure 2 Pressure 3

Polarimetry Results Reflective measurements as low as 0.2% Easily changeable linear polarization Wavelength range 8-62 nm High EUV flux (6 x 10 8 photons/sec at 100 eV) Positioning system accurate to 0.3 mm Harmonics averaged in the y- direction.Data taken at 10º from incidence.

Polarimetry Results

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.

Future Research EUV H 2 O Transmission –Direct characterization of H 2 O transmission constants utilizing the secondary gas cell CXRO Website

Future Research EUV H 2 O Transmission

Future Research EUV H 2 O 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?

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