Interferometric measurements beyond the coherence length of the laser source

Computational analysis of a scalable optically homogeneous free-space interferometer

This study describes a scalable optically homogeneous free-space interferometer. Computationally modeled as an unbroken block of fused silica, the interferometer's six-sided design is simple and intuitive, exploiting total internal reflection and refraction to split and recombine a collimated input beam. During propagation, one portion of the split beam remains within the substrate to act as a reference beam. The second portion of the split beam is exposed to the surrounding environment, enabling real-world environment characterization in real time. Validation of the interferometer concept is performed using numerical and analytical techniques. Based on its scalability and robustness, the proposed interferometer design is primed for applications in atmospheric sensing, passive chemical detection, and spaceborne technologies.

Acousto-Optic-Based Wavelength-Comb-Swept Laser for Extended Displacement Measurements

We demonstrate a novel wavelength-comb-swept laser based on two intra-cavity filters: an acousto-optic tunable filter (AOTF) and a Fabry-Pérot etalon filter. The AOTF is used for the tunable selection of the output wavelength with time and the etalon filter for the narrowing of the spectral linewidth to extend the coherence length. Compared to the conventional wavelength-swept laser, the acousto-optic–based wavelength-comb-swept laser (WCSL) can extend the measureable range of displacement measurements by decreasing the sensitivity roll-off of the point spread function. Because the AOTF contains no mechanical moving parts to select the output wavelength acousto-optically, the WCSL source has a high wavenumber (k) linearity of R² = 0.9999 to ensure equally spaced wavelength combs in the wavenumber domain.