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

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.

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.