Nanostructured Multilayer Coatings for Spatial Filtering

TL;DR

This paper introduces a novel nanostructured multilayer coating that enables near-field spatial filtering of laser beams, offering a compact alternative to traditional far-field filtering methods, especially useful in microlasers.

Contribution

The study proposes and experimentally demonstrates a new multilayer photonic crystal structure for near-field spatial filtering, suitable for integration in microlaser systems.

Findings

Demonstrated a 5 micron thick multilayer structure with near-infrared filtering

Achieved a 2° low angle passband for spatial filtering

Provided a compact solution for intracavity filtering in microlasers

Abstract

Spatial filtering is an important mechanism to improve the spatial quality of laser beams. Typically, a confocal arrangement of lenses with a diaphragm in the focal plane is used for intracavity spatial filtering. Such conventional filtering requires access to the far-field domain. In microlasers, however, conventional filtering is impossible due to the lack of space in micro-resonators to access the far-field. Therefore, a novel concept for more compact and efficient spatial filtering is necessary. In this study, we propose and demonstrate a conceptually novel mechanism of spatial filtering in the near-field domain, by a nanostructured multilayer coating - a 2D photonic crystal structure with a periodic index modulation along the longitudinal and transverse direction to the beam propagation. The structure is built on a nano-modulated substrate, to provide the transverse periodicity. The physical vapor deposition is used to provide self-repeating modulation in the longitudinal direction. We experimentally demonstrate a 5 micron thick photonic multilayer structure composed of nanostructured multiple layers of alternating high- and low-index materials providing spatial filtering in the near-infrared frequencies with 2{\deg} low angle passband. The proposed photonic structure can be considered as an ideal component for intracavity spatial filtering in microlasers.