Self-organisation is an inherent mechanism in all laser systems although it is often overlooked.
The self formation of spatial and spectral modes, competition between modes
and much spatio-temporal dynamics are driven by the intrinsic non-linearity of saturable
gain in the laser amplifier medium coupled with feedback from a resonator structure.
It is highly insightful to consider the growth, extinction and competition of modes in
a laser system as an evolving ecosystem with modes as species growing by stimulated
emission in the gain medium, decaying by intracavity and output coupling losses, and
having to compete for the common, but finite, resource of gain which is supplied by
an external excitation source. The outcome of species competition is a survival-of-the-fittest
that determines the final steady-state output or dynamical set of modes that can
continue to persist. This thesis presents investigations into the design solid-state laser
systems which utilise the inherent dynamics of optical fields and gain media in order to
self-organise the system to operate in a desirable manner.
The Nd:YVO4 bounce geometry laser amplifier is employed throughout this thesis.
A numerical investigation of the thermally induced lensing within the laser crystal is
reported. Optimisation of the geometry parameters is explored as well as investigation
into future developments, such as the utilisation of an additional sapphire crystal to
directly cool the laser crystal pump face. This is shown to theoretically reduce the
horizontal thermally induced lens strengths by a factor of 4.
Single longitudinal mode single longitudinal mode (SLM) ring lasers where the
unidirectionality is imposed either by an extra-cavity ‘parasitic’ pass of the gain media
or by retro-reflection of one of the two outputs are investigated. SLM TEM00 output
powers of up to 20W are demonstrated without the need for a Faraday isolator.
A self-adaptive sensor which allows the measurement of remote surface vibrations
is demonstrated. The two-wave mixing interaction within a saturable gain media is
shown to allow measurement of high frequency phase modulations (>10kHz) whilst
adapting to cancel out low frequency perturbations. This sensor system is shown to
have potential as a remote ultrasound detector as the holographic nature allows high
frequency measurement of the vibrations of rough remote surfaces.
Self-starting self-adaptive lasers, where a four wave mixing interaction within the
saturable gain medium is utilised to generate phase conjugate and aberration corrective
laser systems are experimentally investigated. This work is extended to show that the
gain hologram is capable of adapting to low frequency phase modulations in order to
maintain a high quality output.
A demonstration of self-organised coherent beam combination of two bounce geometry
laser oscillators into a single output beam is reported. A combined output beam
of 35.7W was demonstrated from 94W of pump power. This coherent beam combination
is extended into the technique of phase conjugate self-organised coherent beam
combination (PCSOCBC) where a first demonstration of the combination of two self-starting
self-adaptive modules is reported. It is shown that the adaptive modules allow
efficient beam combination (94%) with a combined output of 27W. As the self-starting
self-adaptive modules do not have predefined spatial or spectral modes it is believed
that this system could be scaled to much higher numbers of modules than is possible with conventional self-organised coherent beam combination
