Control over interfaces in metal oxide optical coatings: the missing piece of the puzzle

Introduction

Multilayer thin-film coatings grant optical elements their specific functionality by forming a high-reflective mirror or a dichroic filter. At the same time, the coatings are the first instance to be damaged by intense laser light, corrosion, or mechanical stress.

Coating Durability

Limited coating durability is heavily influenced by interfaces: the coating – substrate interface and interfaces between layers. Despite a thorough understanding of the properties of the layers’ bulk, control over interfaces is still highly limited. The lack of convenient methods for their characterization makes facilities rely on empirical tricks, thus compromising interface quality and posing severe limitations on the cutting-edge applications of optics.

Project Goals

The COINED project aims to break this barrier by introducing an optical interface characterization with nanometer longitudinal resolution. Such resolution will be enabled by using a structured laser pulse as a source of complex acoustic waves in the coating.

Methodology

The same structured pulse will be used to induce second-harmonic generation (SHG) locally enhanced by the acoustic wave. By using a large set of complex pulses, we will be able to decipher the nonlinear response and the related interface morphology in individual interfaces of multilayer coatings.

Expected Outcomes

With this unprecedented control over interfaces, the project will disclose the role of:

1. Deposition processes
2. Coating post-treatment
3. Aging in the formation of unintended interlayers, defects, or coating restructuring.

Moreover, the ability to continuously monitor and map interfaces throughout coating tests will be the game-changing factor elucidating the processes behind interface deficiencies.

Impact

Interface optimization will open new horizons in the development of space-grade optics, increasing feasible laser power, or extending the lifetime of UV optics. The project will redefine the entire process of thin-film interface optimization with impact covering optics, photovoltaics, or nanotechnology.