Non-destructive evaluation of components often relies on infrared thermography, yet metallic and highly conductive surfaces provide weak radiative contrast and require emissivity calibration. We present an emissivity-independent optical approach for rapid spatiotemporal heat-flow mapping and subsurface anomaly detection using transmission-mode phase measuring deflectometry (PMD). A sinusoidal fringe field is imaged through a transparent sensing medium in thermal contact with a thermally stimulated specimen. Thermal diffusion into the sensing medium creates transient temperature gradients; via the thermo-optic effect, these gradients induce refractive-index gradients that modulate the fringe field, enabling an estimation of the temperature-gradient field from the retrieved phase. A coupled experimental–numerical framework is used for quantitative validation: COMSOL-predicted and PMD-derived ROI-averaged vertical temperature-gradient show close agreement over the 0–3 s early-time window, with a root-mean-square error of 0.074 K/mm. Varying the applied thermal load from 5 K to 55 K yields an approximately linear phase response with a system responsivity of 0.0399 rad per unit applied ΔT_app (defined between the hot-water reservoir and the imaging chamber at t=0). Demonstrations on representative anomaly classes (dissimilar-material interface, localized low-conductivity insert, and void-type discontinuity) show clear localization of subsurface thermal anomalies within the first few seconds after stimulation, supporting rapid anomaly indication when radiative techniques are constrained.

In order to protect the ocean ecosystem, the pursuit of sustainable and self-powered photodetectors is critical for revolutionizing underwater optical communication (UOC) used for environmental hazard sensing. This step enables energy-efficient and real-time detection of marine ecosystem threats such as chemical contamination, oil spill, and eutrophication. Although layered metal dichalcogenides (LMDCs) with exceptional optoelectronic properties and chemical stability are the most suitable materials, their integration into UOC technology remains largely unexplored. To address this, the present study demonstrates and evaluates seawater-immersed photoelectrochemical photodetectors (PEC-PDs) based on SnSe₂, an emerging member from the LMDC family. Direct vapor transport-grown SnSe₂is well characterized in its thin-film form by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and PL spectroscopy, followed by utilization as photoelectrodes in the PEC-PD devices. Fabricated PEC-PDs exhibit a responsivity of 505.74 ± 4.65 μA/W at zero bias and 10.34 ± 0.16 mA/W at 0.4 V bias; they outperform conventional Na₂SO₄-based devices by 21-fold and 82-fold, respectively. To the best of our knowledge, this is the first report presenting an SnSe₂-based PEC-PD utilizing seawater electrolyte and its performance evaluation. A proof-of-concept UOC demonstration of the present study paves the way toward the next-generation green optoelectronic devices for self-sustainable marine technologies.

Measuring refractive index values in transparent liquids has broad applications across industrial, scientific, and technological domains for their identification and characterization. Here a phase measuring deflectometry technique with an artificial fringe system is demonstrated to measure the refractive indices of transparent liquids. It works by projecting a line pattern displayed on a smartphone screen through a test chamber with a unique geometry containing the test solution, which a smartphone camera records. The technique detects changes in refractive index by analyzing phase changes resulting from fringe shifts due to the test solution. The phase difference is determined using Fourier transform-based fringe analysis, and the refractive index is measured by extracting features from the computed phase difference profile and training a regression machine learning algorithm. The developed system is compact, simple, low-cost and accurate. It can measure refractive index with a root mean squared error (RMSE) of 8.5375 × 10⁻⁴, a mean absolute error (MAE) of 7.9 × 10⁻⁴, and a precision of 3.175

This study demonstrates Phase Measuring Deflectometry (PMD) as an optical technique for visualizing heat flow and detecting thermal anomalies in metallic materials. Heat conducted from a thermally loaded sample into an adjacent transparent medium induces spatial refractive index gradients, which distort a projected fringe pattern. These distortions are captured and analysed using PMD, enabling emissivity-independent visualization of the heat flow field. Experimental results on aluminium and structural steel slabs reveal distinct phase signatures linked to thermal conductivity differences. The method offers a compact, non-invasive, and surface-independent alternative to conventional thermography, well-suited for engineering diagnostics and material evaluation.

Shape profiling and thickness information of living cells can provide critical insights about the cells, which can help in their identification and characterization. Most living cells are difficult to image as they are very small and almost transparent. In conventional bright-field microscopy, this issue is resolved by using staining agents, but they can potentially disrupt a cell's natural life cycle. Generally, to address this issue, quantitative phase contrast imaging, such as digital holography is employed, as it provides direct phase information. However, in some practical applications, employing the digital holography technique can become challenging due to stringent optical requirements and its high sensitivity to thickness change. Here, we present phase measuring deflectometry as a microscopy technique by employing a four-step phase-shifting method for shape visualization and thickness measurement of transparent micro-objects. The technique provides phase that is proportional to the deflection angle, which, in turn, depends on the gradient of the optical thickness of the sample. So, the system was calibrated using a 5 μm diameter transparent polystyrene microsphere. A scaling factor was determined by the calibration process, which was then tested by measuring the thickness of a 15 μm diameter transparent polystyrene microsphere. This result obtained with phase measuring deflectometry agrees with the digital holographic microscopy measurement. The proposed technique was further used for visualization and thickness measurement of the red blood cells (RBCs). Based on the available information, the presented technique and algorithm have not been previously exploited for shape visualization and thickness measurement of transparent micro-objects.