Nanostructured materials for laser science

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This research program consists in developing nanostructured materials with simple methods and then using them in solid-state laser devices to enhance their emission characteristics. This research builds on recent progress we have made on the fabrication of nanostructured thin films, the porosity and nanostructure of which can be tailored to tune their optical properties. Using a technique known as glancing angle deposition, we were able to make artificial materials that display very high birefringence and optical activity from initially isotropic materials. We can also characterize the optical constants of these complex materials with ellipsometry. We will use these thin films as internal elements of a laser resonator to produce original emission characteristics with respect to the polarization state, mode profile, and emission spectrum. We also aim at making these solutions power-scalable, i.e., solutions that can withstand high output powers. We will focus on laser-diode-pumped Yb3+-doped ceramics because they have suitable thermal and mechanical characteristics for power scaling and miniaturization. The highly porous nanostructure of the thin films also makes it possible to modify their ''active'' optical characteristics by using a dipping process with luminescent sol-gel solutions. The porous thin film will be used as a scaffold that imposes a specific arrangement for the anisotropic luminescent molecules. As for applications, we will fabricate highly anisotropic thin-film output coupler mirrors that make it possible to realize a compact high-repetition-rate pulsed laser, of which the polarization state, otherwise random, is well defined. We will also use circular Bragg reflection at some prescribed resonance wavelength to obtain laser emission at one single frequency. The resulting enhanced spectral brightness will be useful for enhanced wavelength conversion in a nonlinear crystal or for coherent beam combining for ultra-high-brightness lasers. Combined with the miniaturization potential of microchip lasers design, this research could produce affordable high-brightness laser designs without resorting to large infrastructures. This research program will train students in theoretical and experimental, as well as fundamental and applied aspects at the interface between materials science and optics.