Diffraction of microcylinders and its application in the femtosecond phase mask technique

The side-exposure of microcylinders to a focused Gaussian beam is widely used in both fundamental and applied scientific research, where accurately positioning the beam focus represents a significant challenge. This paper introduces a method based on diffraction patterns to precisely locate the focus within microcylinders. Numerical simulations employing various light propagation algorithms were conducted and experimentally validated. The effectiveness of this method is demonstrated through its application to the femtosecond laser phase mask technique (PMT) for inscribing fiber Bragg gratings (FBGs). A detailed analysis of the complex diffraction in the PMT system is provided, offering essential guidance for optical alignment and focus positioning. This approach is directly applicable to the automated fabrication of FBGs in fibers of varying diameters. The work presents an in-depth insight into the diffraction of microcylinders, with potential applications in laser manufacturing and precision measurement.