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ISBN 978-3-8439-1400-0

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978-3-8439-1400-0, Reihe Physik

Fabian Reichert
Praseodymium- and Holmium-Doped Crystals for Lasers Emitting in the Visible Spectral Region

182 Seiten, Dissertation Universität Hamburg (2013), Softcover, A5

Zusammenfassung / Abstract

The topic of this work is the investigation of novel gain media for the realization of solid state lasers directly emitting in the visible spectral region. For this purpose, the rare-earth ions Pr and Ho were chosen.

For the Pr-ion the oxide host materials SrAl12O19 (SRA), CaAl12O19 (CAlO), and LaMgAl11O19 (LMA) were chosen. Additionally the low-phonon fluoride material LaF3 was employed. For the Ho-ion, LiLuF4 (LLF) and LaF3 were used as host systems.

The active media were characterized in terms of ground state absorption (GSA), emission, and excited state absorption (ESA). For the Pr- as well as for the Ho-doped systems absorption bands in the blue spectral range suitable for pumping by InGaN laser diodes or frequency doubled optically pumped semiconductor lasers were found. Emission measurements showed that the Pr-doped systems exhibit distinct emission peaks in the blue to deep red spectral region which were not influenced by ESA. The Ho-doped materials exhibit emission peaks in the green spectral range where GSA is also present. Therefore gain spectra were derived and revealed that for both Ho-doped systems inversion levels of at least 20% are required to achieve gain. The wavelength region in which gain can be expected is not influenced by ESA. In addition, measurements of the decay dynamics revealed maximum quantum efficiencies of less than 40% (LLF) and approximately 75% (LaF3).

Laser experiments were carried out with all active media. With Ho:LLF it was not possible to achieve green laser emission. However, with Ho:LaF3 room temperature laser operation in the green spectral region was demonstrated for the first time with a Ho-doped crystalline system.

Laser operation was demonstrated with all Pr-doped host materials. Best results were obtained with Pr:SRA where more than 1W of output power and slope efficiencies of almost 60% were realized in the red and deep red spectral region. Furthermore it was possible to demonstrate cw laser operation of a Pr-doped oxide in the green spectral range for the first time at room temperature. In addition, experiments were carried out in a thin disk setup and it was possible to realize first laser operation in this geometry of a Pr-doped gain medium. Waveguiding structures in Pr:SRA were fabricated by fs-laser inscription. With these waveguides laser operation was demonstrated in the red spectral region with an output power of more than 1W at almost 40% slope efficiency.