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Optical interferometry has emerged as a cornerstone technology for high-precision length measurement, offering unparalleled accuracy in various scientific and industrial applications. This review provides a comprehensive overview of the latest advancements in optical interferometry, with a focus on grating and laser interferometries. For grating interferometry, systems configurations ranging from single-degree- to multi-degree-of-freedom are introduced. For laser interferometry, different measurement methods are presented and compared according to their respective characteristics, including homodyne, heterodyne, white light interferometry, etc. With the rise of the optical frequency comb, its unique spectral properties have greatly expanded the length measurement capabilities of laser interferometry, achieving an unprecedented leap in both measurement range and accuracy. With regard to discussion on enhancement of measurement precision, special attention is given to periodic nonlinear errors and phase demodulation methods. This review offers insights into current challenges and potential future directions for improving interferometric measurement systems, and also emphasizes the role of innovative technologies in advancing precision metrology technology.

Ti2AlC is a typical MAX (M: early transition metal, A: main group element, and X: carbon and/or nitrogen) phase with ceramic and metallic properties due to its unique nano-layered structure. In order to investigate the interaction behavior between Ag and Ti2AlC, a sessile drop experiment was conducted at 1080 °C for 5 min. The atomic rearrangement occurred at the Ag–Ti2AlC interface was revealed using high-angle annular dark-field scanning transmission electron microscopy coupled with high-resolution transmission electron microscopy analysis. The results show that Ag nanoclusters generally appeared in most of the Ag–Ti2AlC interaction regions thermally processed at 1080 °C. In addition, Ag can also substitute for Al and Ti atoms in the Ti2AlC, promoting local structural decomposition of the Ti2AlC and producing 4H–Ag with a hexagonal close-packed (hcp) structure. Additionally, Al atoms released from the Ti2AlC lattices can dissolve locally into the liquid Ag, particularly at the grain boundaries. When the loss concentration of Al exceeded the critical level, the Ti2AlC started to decompose and the residual Ti6C octahedrons and Al atoms recombined, giving rise to the production of anti-perovskite Ti3AlC with a cubic structure. Lastly, the discrepancy in substitution behavior of Ag in the Ti2AlC was compared when thermally processed at different temperatures (1030 °C and 1080 °C). This work contributes to the understanding of the intrinsic stability of Ti2AlC MAX ceramics under high-temperature treatment.

We report on a frequency-comb-referenced absolute interferometer which instantly measures long distance by integrating multi-wavelength interferometry with direct synthetic wavelength interferometry. The reported interferometer utilizes four different wavelengths, simultaneously calibrated to the frequency comb of a femtosecond laser, to implement subwavelength distance measurement, while direct synthetic wavelength interferometry is elaborately introduced by launching a fifth wavelength to extend a non-ambiguous range for meter-scale measurement. A linearity test performed comparatively with a He–Ne laser interferometer shows a residual error of less than 70.8 nm in peak-to-valley over a 3 m distance, and a 10 h distance comparison is demonstrated to gain fractional deviations of ~3 × 10−8 versus 3 m distance. Test results reveal that the presented absolute interferometer enables precise, stable, and long-term distance measurements and facilitates absolute positioning applications such as large-scale manufacturing and space missions.