Camille Petite will defend his PhD thesis "Optical thin film components for high power continuous wave lasers" on Thursday April 14th at 02:00 p.m. in Ponte amphitheater, St Jérôme campus, Aix Marseille University.
The Jury will be composed of:
Pierre BOURDON, Directeur de recherche – ONERA, Rapporteur
Laurent PINARD, Ingénieur de recherche – LMA, Rapporteur
Marine CHOREL, Ingénieure-chercheuse – CEA, Examinatrice
Patricia SEGONDS, Professeure – Institut Néel, Examinatrice
Hélène KROL, Ingénieure-Docteure – CILAS, Examinatrice
Julien LUMEAU, Directeur de recherche CNRS – Institut Fresnel, Directeur de thèse
Laurent GALLAIS, Professeur ECM – Institut Fresnel, Directeur de thèse
Abstract:
High power continuous wave lasers have a wide range of industrial, military and scientific applications. The increase in power of Ytterbium-doped fiber lasers allows to reach power levels of several hundred kilowatts at a wavelength of 1 µm. However, increasing the power of these lasers requires the development of optical components that handle these power levels.
Among the various optical components of a laser system, thin-film optical filters are essential elements because of the large number of optical functions that they offer: anti-reflection, mirrors, dichroic... Despite absorption levels in the order of parts per million (ppm) in the films, high power laser heating induced is a limitation for the laser performance, ranging from wavefront deformation to eventual damage of the optics.
To meet the new requirements associated with the use of very high power continuous wave lasers, the heating mechanisms and consequently the absorption of thin film stacks must be controlled. This results in the need to develop a specific metrology capable of providing reliable measurements at the ppm level and below.
In this work we present the development of a method called Lock-In Thermography, (LIT) that is based on the use of a synchronous detection technique coupled to infrared thermography in order to image the temperature variations on large surfaces and to locally extract absorption values, by applying a calibration procedure.
This instrument uses a multi-pass setup allowing to recycle the laser beam power and thus to increase the total absorbed power leading to an improvement of the signal to noise ratio. We have applied this system to analyze different samples (substrates, single layers, mirrors and antireflection coatings). A modification of the LIT set-up also allowed us to perform an absorption mapping of macro defects. Finally, ways to minimize the intrinsic absorption of thin-film optical components are explored.
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