Yb:tungstate waveguide lasers
Abstract
Lasers find a wide range of applications in many areas including photo-biology,
photo-chemistry, materials processing, imaging and telecommunications. However,
the practical use of such sources is often limited by the bulky nature of existing
systems. By fabricating channel waveguides in solid-state laser-gain materials more
compact laser systems can be designed and fabricated, providing user-friendly
sources. Other advantages inherent in the use of waveguide gain media include the
maintenance of high intensities over extended interaction lengths, reducing laser
thresholds.
This thesis presents the development of Yb:tungstate lasers operating around 1μm in
waveguide geometries. An Yb:KY(WO₄)₂ planar waveguide laser grown by liquid
phase epitaxy is demonstrated with output powers up to 190 mW and 76 % slope
efficiency. This is similar to the performance from bulk lasers but in a very compact
design. Excellent thresholds of only 40 mW absorbed pump power are realised. The
propagation loss is found to be less than 0.1 dBcm⁻¹ and Q-switched operation is also
demonstrated.
Channel waveguides are fabricated in Yb:KGd(WO₄)₂ and Yb:KY(WO₄)₂ using
ultrafast laser inscription. Several of these waveguides lase in compact monolithic
cavities. A maximum output power of 18.6 mW is observed, with a propagation loss
of ~2 dBcm⁻¹. By using a variety of writing conditions the optimum writing pulse
energy is identified. Micro-spectroscopy experiments are performed to enable a fuller
understanding of the induced crystal modification. Observations include frequency
shifts of Raman lines which are attributed to densification of WO₂W bonds in the
crystal.
Yb:tungstate lasers can generate ultrashort pulses and some preliminary work is done
to investigate the use of quantum dot devices as saturable absorbers. These are shown
to have reduced saturation fluence compared to quantum well devices, making them
particularly suitable for future integration with Yb:tungstate waveguides for the
creation of ultrafast, compact and high repetition rate lasers.
Type
Thesis, PhD Doctor of Philosophy
Rights
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