The snapshot generalized ellipsometer encodes polarization modulation in the wavelength domain rather than in the time domain, enabling truly instantaneous measurements. It can operate in both transmission and reflection modes, simultaneously measuring nine elements of the Mueller matrix spectroscopically. The system employs two high-order retarders—one in the polarization state generator (PSG) and another in the polarization state analyzer (PSA).
How this differs from other Snapshot approaches?
Most other snapshot techniques operating in the wavelength domain rely on channeled spectropolarimetry, where the polarization information is encoded as a periodic modulation in the spectrum and retrieved via Fourier analysis. Our approach, in contrast, is based on a generalized ellipsometry framework that directly relates the spectrally encoded measurements to the Mueller matrix elements through a well-defined algebraic model. Furthermore, by using two high-order retarders—one in the PSG and one in the PSA—the system maintains high modulation efficiency across a broad spectral range, enabling the simultaneous retrieval of a larger set of polarization information in both transmission and reflection geometries.
What elements does it measure?
The following 9 elements can be measured
How fast does it measure?
The measurement speed is limited only by the CCD sensor’s exposure time and, to a lesser extent, by the data transfer rate between the CCD and the computer. In our system, measurements are routinely acquired every 10 ms, approximately 100 times faster than conventional systems.
How well does it measure?
Because our method relies on spectral modulation, the measurement quality is directly linked to the system’s spectral resolution. Data inversion is performed over spectral windows: narrow windows provide high spectral resolution but worsen the numerical conditioning, whereas wider windows improve resilience to noise and errors but are unsuitable for samples with strong spectral variations. An optimal balance must therefore be found.
Owing to the absence of moving parts, stochastic errors are typically small and comparable to those of state‑of‑the‑art commercial systems, while systematic errors can be larger due to the trade‑offs inherent in spectral window selection and inversion. The following comparison shows the larger systematic errors.
Can it perform more challenging measurements?
Yes. In addition to routine thickness measurements, the system is well suited for more demanding applications. For example, the images below show its performance with an anisotropic crystal (x‑cut TiO₂), which exhibits cross‑polarization effects that vary with the crystal’s azimuthal orientation. These signals will be very small.