Thin-film multilayers deposited on a wafer induce bending due to residual and thermal stresses that strongly depend on process conditions. The resulting curvature can be measured optically. We present a closed-form analytical model that relates the measured curvature to the residual stresses in individual layers. Using a small set of curvature measurements, layer-resolved residual stresses can be extracted without resource-intensive finite-element model simulations.

The size-of-source effect (SSE) is a systematic error requiring slow labor-intensive measurements. We propose a continuous approach using an iris diaphragm. Our method matched the accuracy of the traditional discrete method while providing more data and a reduction in measurement time. The method has no significant sensitivity to frame rate changes. Transient responses were observed using a neutral density filter, raising questions on how to measure and correct SSE in such configurations.

Methane plays an important role in global warming, and tracing its sources requires precise analysis of its isotopic fingerprint. In this study, we demonstrate the foundation of a system based on optical feedback cavity-enhanced absorption spectroscopy that achieves the stability needed for accurate isotope measurements. This work shows the potential of the method for future climate studies and environmental monitoring.