Optical interference filters offer a very broad range of optical functions for the control of the spectral
properties of light. With the last 15‐year improvement of both the design techniques and the
manufacturing systems, the complexity of filters has dramatically increased. In particular, the
combination of stable deposition processes (e.g. sputtering technique) and in‐situ optical monitoring
has allowed fabricating high performances filters that can be composed with several hundreds of
layers. The filters structures are then no longer periodic and can exhibit a very broad range of
thicknesses ranging from a few nanometers to a few hundreds of nanometer for filers in visible and
near‐IR range.
To precisely control the thickness of each layer, there are, as of today, two classes of optical monitoring
techniques: monochromatic and broadband optical monitoring. The first one relies on an in‐situ
measurement of the transmitted (or reflected) intensity at a single wavelength and, in this case, the
choice of the proper wavelength is a critical criterion that will affect the precision of the control. The
second one relies on an in‐situ measurement of the transmitted (or reflected) intensity over a broad
spectral range and, in this case, the choice of the proper stopping condition is a critical criterion that
will affect the precision of the control.
In this thesis, we propose to explore the combination of both monochromatic and broadband optical
monitoring techniques. These developments will be done in collaboration between the Thin Film
Research Team at institut Fresnel in Marseille, France
(https://www.fresnel.fr/spip/spip.php?article1487) and Bühler company (Bühler France and the R&D
department of Bühler/Leybold Optics in Alzenau, Germany
(https://www.buhlergroup.com/global/en/process‐technologies/high‐vacuum‐thin‐filmcoating/
about‐buehler‐leybold‐optics.htm). The developments will be done on a Bühler HELIOS
machine (Plasma Assisted Reactive Magnetron Sputtering) and with a brand new broadband optical
monitoring system under development at Bühler. The thesis will thus consist in developing and
experimentally implementing new monitoring techniques.
The Ph.D. thesis will be funded by a CIFRE grant (http://www.anrt.asso.fr/fr/cifre‐7843), meaning that
the student will be hired for three years by Bühler Company. The candidate is then expected to spend
most of his time (80%) at institut Fresnel with some shorts stays at Bühler (20%).
The candidate must have a Master in Science with good knowledge in optics, programming and if
possible in optical thin films. The candidate must also be fluent in English and German (French
optional).
This thesis will be supervised by Dr Thomas Begou and Julien Lumeau at institut Fresnel and Dr Harro
Hagedorn and Detlev Arhilger at Bühler Alzenau.
Send resume, cover letter and M1 and M2 transcripts to: julien.lumeau@fresnel.fr

PhD thesis topic – IF-Bühler