High-attenuation and polarization-independent beam sampling technique based on evanescent light coupling

A beam sampling technique based on evanescent light coupling was developed. This technique uses an evanescent coupling element (ECE) with high laser durability, making it suitable for kW-class lasers. In this study, an ECE was fabricated using a pair of glass prisms with optimized geometry to achieve polarization-independent optical properties. Results showed that a single ECE can provide laser power attenuation an order of magnitude greater than that of a conventional Fresnel beam sampler—based on Fresnel reflection—at a near-infrared laser wavelength, regardless of polarization. Additionally, the use of ECEs contributes to a reduction in the overall size of optical components. This beam sampling technique shows promise for applications not only with high-power, randomly polarized lasers such as kW-class fiber lasers but also with lasers featuring well-defined polarization, as used in precision material processing.