Extreme Ultraviolet Polarimetry Extreme Ultraviolet Polarimetry Utilizing High-Order HarmonicsUtilizing High-Order Harmonics

Nicholas Herrick, Nicole Brimhall, Justin Peatross

Brigham Young University

OutlineOutline

• 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)Extreme Ultraviolet (EUV)

121 nm - 10 nm

Why Study EUV Optical Constants?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 ConstantsFinding Optical Constants

Reflectance as a function of– Angle– Polarization– Wavelength

Finding Optical ConstantsFinding Optical Constants

BYU PolarimetryBYU Polarimetry The BYU polarimeter is a combination of three optical systems:

- High-intensity laser - High harmonic generator - Polarimeter

High-intensity Laser SourceHigh-intensity Laser Source

800 nm, 30 x 10-15 sec pulse width

High Harmonic GenerationHigh 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

BYU EUV PolarimeterBYU EUV Polarimeter

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

BYU EUV PolarimeterBYU EUV Polarimeter

EUV Controllable AttenuationEUV 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 AttenuationEUV 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

EUV Controllable AttenuationEUV 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 AttenuationEUV 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 ResultsPolarimetry 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.

Polarimetry ResultsPolarimetry Results

SummarySummary

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 ResearchFuture Research

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

http://henke.lbl.gov/optical_constants/intro.html

CXRO Website

Future ResearchFuture Research

EUV H2O Transmission

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5 10 15 20 25 30 35 40 45 50 55 60 65

Wavelength (nm)

Transmission (%)

H2O2H2O

Future ResearchFuture 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?

AcknowledgementsAcknowledgements

Principle contributors:– Dr. Justin Peatross– Nicole Brimhall– Dr. David Allred

The National Science Foundation The College of Physical and Mathematical

Sciences, BYU