Innovative Techniques for the Metrology of Optical Coating PropertiesMichel Lequime, Institut Fresnel
Since the end of the 1990s, the simultaneous availability of powerful optical filter design software and reliable thin-film deposition techniques using energetic processes such as ion beam assistance, ion beam sputtering or magnetron sputtering have made possible the manufacture of high-performance optical interference coatings comprising a great number of layers, from one hundred up to a few thousand. For highly demanding applications such as observation of the Earth from space, wavelength multiplexing of high data rate optical telecommunications channels, study of the organization of living matter at the cellular scale, or interferometric detection of gravitational waves, it is necessary to confirm by very accurate measurements the theoretical figures provided by the design, especially for some key filter parameters like optical density in the blocking regions steepness of band edges , or wavelength and angle resolved scattering.
The objective of this course is first to recall some fundamentals on the detection of optical signals, and second to use these basics to explain the structure and the performances of spectrophotometric apparatus developed in the three following goals
• Ultra-wide range measurement of the spectral transmittance of optical interference filters
• Angle and wavelength resolved measurement of the light scattered by optical components
• Detection of localized defects at the surface of a plane optical window using spatially and angularly resolved detection of scattered light
This course is of use for anyone who are interested in the development of high-level spectrophotometric instrumentation. It is addressed to junior and senior scientists as well as to engineer and science students of higher terms.
Michel Lequime is Eméritus Professor at Centrale Marseille, a French engineer high school and senior scientist in the Concept team of Institut Fresnel. Currently, his research interests concern the comprehensive characterization of optical components through spatially and angularly resolved light scattering measurements and the theoretical study of optical properties of thin-film stacks including metamaterials layers. He is credited with twenty-six patents and three hundred publications and presentations in the areas of non-linear optics, space optics, fiber optic sensors, scattering phenomena and optical interference coatings. He is a member of the OSA and SPIE, and has served as Secretary of the Board of the French Optical Society (SFO, 2009-13).
PDF download: SC_FOC2023_1
Design coating and monitoring in state-of-the-art coating processes
Marco Jupé, Laser Zentrum Hannover
Optical interference coatings form the basis for Modern Optics. Regardless of the concrete application, almost all optical surfaces are finished with dielectric coatings. In many cases, the coatings are even solely responsible for functionality.
To produce a coating, one must always follow the triad between optical design, coating process and monitoring, which is often verified by ex situ characterization. The course will be limited to the first three steps of coating fabrication. That is, it will start with a brief and very general overview of how optical interference coatings work. Subsequently, different coating processes will be discussed. The special focus here is on the processes used for high quality laser optics. In turn, the physical processes are dominant. However, the current developments in optical coatings will also be considered and a short excursion into ALD (atomic layer deposition) will be given. The third part deals with the monitoring of layer growth. Besides a short historical overview, the focus is on the application of optical broadband monitoring. This now forms the basis for most sputter coating processes, but the process has also become established in ion-assisted and, in some applications, conventional coating, especially in custom production. In the meantime, the monitors are partly flanked by powerful re-calculation and re-optimization programs. These are capable of compensating for even major coating errors in the design.
The highlight of coating technology at present is certainly the direct measurement of GDD during the coating
process. Here, too, a brief introduction to the equipment technology and the application is given.
Marco Jupé has been working at the Laser Zentrum Hannover e.V. (LZH) since 2001. From 2001 to 2012, he
worked as a scientist, and since 2012, he has served as the Head of the Photonic Materials Group in the Optical Components Department. His main research areas include the development of simulation models, laser-induced damage and properties of optical materials, non-linear characteristics of dielectric materials, and experimental ion coating processes. Dr. Marco Jupé has published 40 journal articles and 88 conference papers in these areas.
PDF download: SC_FOC2023_2