Polarization-ratio reflectance measurements in the extreme ultraviolet

Abstract

We demonstrate a technique for determining optical constants of materials in the extreme UV from the ratio of p-polarized to s-polarized reflectance. The measurements are based on laser-generated high-order harmonics, which have easily rotatable linear polarization but that are prone to brightness fluctuations and systematic drifts during measurement. Rather than measure the absolute reflectance, we extract the optical constants of a material from the ratio of p-polarized to s-polarized reflectance at multiple incident angles. This has the advantage of dividing out long-term fluctuations and possible systematic errors. We show that the reflectance ratio is as sensitive as the absolute reflectance to material optical properties.

Measured optical constants of copper from 10 nm to 35 nm

“…[18] and the polarization-ratio-reflectance method described in Ref. [19]. This instrument uses high-intensity laser pulses (800 nm, 10 mJ, 35 fs at 10 Hz) focused into a noble gas to produce polarized and directional high-harmonics with wavelengths distributed throughout the EUV.…”

Characterization of optical constants for uranium from 10 to 47 nm

“…[14] and the polarization-ratio reflectance 0003-6935/10/091581-05$15.00/0 © 2010 Optical Society of America measurement technique described in Ref. [15]. To our knowledge, this is the first time the optical constants of elemental uranium have been measured in this wavelength range.…”

“…After the pressure dropped below 10 −6 Torr, the shutter was opened for 10 s. This time frame allowed a deposition of approximately 2-3 nm of uranium metal (approximately 0:2 nm=s). The sample was deliberately made thin to allow for a more accurate determination of optical constants (see [15]). The sample was rotated back into the measurement chamber within minutes of deposition and without breaking vacuum.…”

“…The sample was rotated back into the measurement chamber within minutes of deposition and without breaking vacuum. The polarization-ratio reflectance measurements were then performed on samples (at room temperature) using the technique described in [15]. After the measurements, the uranium samples were exposed to the atmosphere and the thickness of the oxidized sample was measured with spectroscopic ellipsometry.…”

“…Each point represents an average of 400 laser shots at an effective repetition rate of approximately 3 Hz (because of laser energy discrimination of AE10% described in [14]). The lines show best-fit curves calculated from the model described in [15] with n and κ for the test layer taken as free parameters in a least-squares fitting algorithm (MATLAB nlinfit). The film thickness was held stationary in the fits at the value calculated from the measured thickness of the oxidized layer (as described above).…”