Abstract
We present a setup for time-resolved spectroscopic ellipsometry in a pump-probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer-sample-compensator-analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump-probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV-3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues.
Highlights
Ellipsometry is a well-established method to obtain thin-film properties and material optical constants, which, in particular, allows gaining insights into the electronic structure of materials
We present a setup for time-resolved spectroscopic ellipsometry in a pump–probe scheme using femtosecond laser pulses
The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump–probe delays and polarization settings
Summary
Ellipsometry is a well-established method to obtain thin-film properties and material optical constants, which, in particular, allows gaining insights into the electronic structure of materials. Commercial laser technology has matured sufficiently to make supercontinuum generation (SCG) in transparent crystals a versatile broadband optical probe with femtosecond laser pulses.. Commercial laser technology has matured sufficiently to make supercontinuum generation (SCG) in transparent crystals a versatile broadband optical probe with femtosecond laser pulses.18,19 This opens the path for ultrafast pump–probe spectroscopic ellipsometry. We present a setup for pump–probe ellipsometry with femtosecond white light pulses ranging from nearinfrared (NIR) through the visible (VIS) to the near-ultraviolet (NUV). It is capable of obtaining pump-induced transient changes in the linear optical response of a wide range of materials and sample types. While the narrow-band pump pulses are focused onto the sample by a lens, the broadband probe pulses are focused by a 90○ off-axis parabolic
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