Extreme-ultraviolet polarimeter utilizing laser-generated high-order harmonics

Abstract

We describe an extreme-ultraviolet (EUV) polarimeter that employs laser-generated high-order harmonics as the light source. The polarimeter is designed to characterize materials and thin films for use with EUV light. Laser high harmonics are highly directional with easily rotatable linear polarization, not typically available with other EUV sources. The harmonics have good wavelength coverage, potentially spanning the entire EUV from a few to a hundred nanometers. Our instrument is configured to measure reflectances from 14 to 30 nm and has approximately 180 spectral resolution (lambda/Delta lambda). The reflection from a sample surface can be measured over a continuous range of incident angles (5 degrees-75 degrees). A secondary 14 cm gas cell attenuates the harmonics in a controlled way to keep signals within the linear dynamic range of the detector, comprised of a microchannel plate coupled to a phosphorous screen and charge coupled device camera. The harmonics are produced using approximately 10 mJ, approximately 35 fs, and approximately 800 nm laser pulses with a repetition rate of 10 Hz. Per-shot energy monitoring of the laser discriminates against fluctuations. The polarimeter reflectance data agree well with data obtained at the Advanced Light Source Synchrotron (Beamline 6.3.2).

Measured optical constants of copper from 10 nm to 35 nm

“…We made these measurements using the laser-high-harmonics-based polarimeter described in Ref. [18] and the polarization-ratio-reflectance method described in Ref. [19].…”

“…At each angle, 400 laser shots were averaged at an effective frequency of about 3 Hz (owing to energy discrimination of our 10 Hz laser source as described in Ref. [18]).…”

Characterization of optical constants for uranium from 10 to 47 nm

“…Figure 2 shows the ratio reflectance and fit for the uranium film at representative wavelengths of 18.6 and 34:8 nm. 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).…”

“…This instrument, which is described in Ref. [14], uses 800 nm, 10 mJ, 35 fs, and 10 Hz laser pulses focused into a noble gas to produce polarized and directional high-harmonic light in the EUV wavelength range. Many harmonic frequencies (with wavelengths distributed throughout the EUV) simultaneously emerge from the focus in a collimated beam embedded in the residual laser beam.…”

“…[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].…”