Developments in THz Range Ellipsometry

Abstract

Ellipsometry is a technique whereby the measurement of the two orthogonal polarization components of light reflected at glancing incidence allows a characterization of the optical properties of a material at a particular frequency. Importantly, it obviates the need for measurement against a standard reference sample, and so can provide reliable spectroscopic information even when surface morphology is unknown, of marginal quality and/or a reference is unavailable. Although a standard technique in the visible range, it has not been widely applied in the Terahertz (THz) spectral range despite its potential utility. This is largely because of the technical difficulties that these frequencies present. This review details recent progress in the implementation of THz range ellipsometry. We discuss a variety of configurations including various kinds of laboratory and facility based sources using both continuous wave and pulsed spectroscopic methods. We discuss the general problems encountered when trying to import the methodologies of visible range ellipsometry to the THz range and give examples of where the technique has been successful thus far.

Study of novel electronic materials by mid-infrared and terahertz optical Hall effect

“…The main difficulties for the implementation comes from a lack of high intensity and quality sources, a high background black-body radiation contamination and limited choices for polarizing optical elements [43,44]. Since the wavelength of the THz radiation is in the range of milimeters, optical elements and samples commonly used in SE measurements can cause diffraction [44]. Furthermore, for highly coherent light sources, standing waves can form in the optical system, which has highly detrimental effect on the performance of the ellipsometer.…”

Polarization-variable emitter for terahertz time-domain spectroscopy

“…The development of polarization-sensitive terahertz (THz) time-domain spectroscopy (TDS) is important for non-destructive testing (NDT) of materials, which are opaque in UV/Vis and IR spectral regions, but having the optical anisotropy properties in THz range [1][2][3][4]. For example, the production, stress, and damage induced linear dichroism [5,6], birefringence [7,8], or ellipticity [2,9] can be used to understand the quality and state of pure polymers, their composites, crystals, or dielectric and semiconductor materials. The THz-TDS also has additional advantages such as non-ionizing and harmless nature, the ability to operate at ambient conditions, and to provide the rich information on materials dielectric properties.…”

Spectroscopic ellipsometry for active nano- and meta-materials

“…Measurements in the vacuum UV [10,11] and in a broad spectral range in the IR [12][13][14][15] have also been made possible either using "home-built" or commercial setups. More recently and although still being in its infancy, THz SE [16,17] has already provided promising results. Performing measurements of a material's dielectric function ε (assuming the most simple case of a compositionally homogeneous and isotropic medium) in such a broad spectral range from the vacuum UV to the THz (see Figure 1B) yields rich information about the material's electronic structure.…”