Fast Mueller matrix infrared ellipsometry using quantum cascade laser: Applications in material characterization

We present a high-speed infrared spectroscopic ellipsometer using a tunable quantum cascade laser (QCL), leveraging its high brightness for potential in situ and in-line monitoring applications. The instrument employs a dual-rotating-element configuration comprising an achromatic Fresnel rhomb-type rotating compensator and a rotating analyzer, enabling acquisition of 3 × 4 Mueller matrix elements over a wavelength range defined by the installed QCL laser modules. We demonstrate the measurement speed of the QCL ellipsometer and its advantages relative to conventional Fourier-transform infrared ellipsometry through a series of case studies, including measurements of complex molecular vibrations of acrylic and polycarbonate, anisotropic phonon absorption of LiNbO3 single crystal, and its temperature-dependent response. Additionally, we perform time-dependent measurements during the thermal growth of an SiO2 film on Si, highlighting the instrument's capability for real-time process monitoring.