ISBN 9783843927482

978-3-8439-2748-2, Reihe Physik

Sven H. Waeselmann
Waveguiding and Laser Action in Rare-Earth-Doped Sesquioxide and Sapphire Films

149 Seiten, Dissertation Universität Hamburg (2016), Softcover, A5

Zusammenfassung / Abstract

The research in integrated optical devices based on novel rare-earth (RE) doped crystalline materials is of great interest as these can exhibit superior properties compared to the materials forming today's industry standards.

The subject of this thesis was the growth and characterization of active waveguiding films based on RE3+-doped indium(III) oxide and alpha-Al2O3 grown via pulsed laser deposition (PLD). While the mineralogical term of the hexagonal alpha-modification of Al2O3 is corundum, in laser physics, alpha-Al2O3 is usually called sapphire. Both, In2O3 and RE3+-doped sapphire pose diffculties when grown from a thermal equilibrium. Working far apart the thermal equilibrium PLD has proven to be a viable method to synthesize these materials.

Films with a thickness of up to 2:6 µm were deposited in a heteroepitaxial scheme for RE3+-doped In2O3 and lattice matched (In,Y)2O3 films on Lu2O3 as well as homoepitaxial with RE3+-doped sapphire films grown on sapphire substrates. The growth was monitored using high-energy electron diffraction for in-situ characterization of the crystal structure. A reflectometer allowed for analyzation of both thickness and refractive index of the films. Further characterization with respect to the film structure was performed by X-ray diffraction and atomic force microscopy.

Spectroscopy of Nd3+:alpha-Al2O3 films revealed high emission cross-sections of up to 1 x 10^-18 cm^2 and 5 x 10^-19 cm^2 for the 4F3/2 -> 4I11/2 transition around 1 µm for sigma- and pi-polarization, respectively. The waveguide scattering losses were determined to be as low as 3 dB/cm for the wave-guiding sapphire and In2O3 films.

In (1 at.%)Nd3+:alpha-Al2O3, continuous-wave laser emission at 1092 nm and 1096 nm has been realized in films grown on differently oriented sapphire substrates allowing for either the sigma- or pi-polarization to be addressed, respectively.

The samples allowed for lasing in a planar waveguide geometry with feedback solely provided by the Fresnel reflection of the waveguide end facets. In pi-polarization laser oscillation started at threshold pump power of 142mW with a slope effciency with respect to the incident pump power of 7.5%. In sigma-polarization laser oscillation started at 635mW of incident pump power with a slope effciency of 4%.

While the laser performance has yet to be improved, laser action has for the first time been demonstrated in rare-earth-doped sapphire.