Focal field analysis of highly multi-mode fiber beams based on modal decomposition

Abstract

In this work, a numerical modal decomposition approach is applied to model the optical field of laser light after propagating through a highly multi-mode fiber. The algorithm for the decomposition is based on the reconstruction of measured intensity profiles along the laser beam caustic with consideration of intermodal degrees of coherence derived from spectral analysis. To enhance the accuracy of the model, different approaches and strategies are applied and discussed. The presented decomposition into a set of LP modes enables both the wave-optical simulation of radiation transport by highly multi-mode fibers and, additionally, the analysis of free-space propagation with arbitrarily modified complex amplitude distributions.

Photonic shaping tools for large-scale micro-machining

“…The starting point of every design for a laser-optical tool is the modeling of the light source. 18,19 When ultrafast lasers are considered the task seems easy. To generate ultrashort laser pulses it is straightforward to use radiation from oscillators operating in the spatial single-mode regime-typically a light state that is very close to a fundamental Gaussian beam.…”

Structured light for ultrafast laser micro- and nanoprocessing

“…14. Beam diagnostics may base on field reconstructions from caustic- 8,104 or wavefront measurements 105,106 as well as from modal analysis. 107,108 In the simplest case, a camera monitors the actual focus quality at a fixed z-position.…”

“…More sophisticated spatial distributions become especially attractive when considering efficient, industry-compatible concepts intended to yield high throughputs. [5][6][7][8] Thus, in addition to the remarkable temporal properties of ultrashort pulsed lasers, there is a need for tailored focus distributions in all spatial degrees of freedom. 6,9,10 Recently, the term "structured light" has been used to cover advanced beam shaping concepts in which all spatial and temporal properties of laser radiation are manipulated to achieve tailored light states.…”

Phase retrieval algorithm applied to high-energy ultrafast lasers

“…4) from different ultrafast lasers and consider the radiation to be composed of a single optical field (complete coherence; for partial coherence see Ref. [23]). Corresponding pulse durations are longer than 100 fs so that a description by a single wavelength (quasimonochromatic case) is valid in a good approximation.…”