Optical Properties & Applications of Nanomaterials
Advances in materials science are enabling the fabrication of new materials with external dimensions on nanometer length scales, known as nanomaterials, which possess remarkable optical and electrical properties. While graphene is perhaps the best known example, it is only one of a wider family of nanomaterials, also including carbon nanotubes and few-layer transition metal dichalcogenides such as molybdenum disulphide (MoS2), each with distinct yet complementary properties.
We have performed fundamental measurements (in collaboration with the Cambridge Graphene Centre and the Hybrid Nanomaterials Engineering Group, UK) showing that these materials can possess a high nonlinearity across a wide range of wavelengths. This suggests that they could be exploited to develop new photonic devices and technologies. Work to date has shown that nanomaterials are ideal saturable absorbers for ultrashort laser pulse generation by mode-locking and Q-switching mechanisms.
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Short-Pulse Fibre Laser Development
Fibre lasers have revolutionised modern science and technology: they underpin the global telecommunications sector and play a key role in medical, industrial and research environments. However, ever more demanding end-user requirements, particularly for pulsed (i.e. Q-switched and mode-locked) laser sources, are driving research to improve the temporal and spectral versatility of such lasers.
We are developing a new mode-locked laser architecture by combining nanomaterial-based saturable absorbers with ultralong ring cavities, lowering the laser repetition rate to produce high-energy giant-chirped pulses. Such pulses have been amplified with minimal distortion and compressed to raise the peak-power (in collaboration with Ecole Polytechnique de Montréal, Canada), making them suitable for nonlinear applications such as supercontinuum generation.
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Nonlinear Wave Dynamics in Optical Fibre
The interaction between materials and low-intensity light is linear. In optical fibre, however, in combination with high peak-power laser pulses, light can be tightly confined to create very high intensities, resulting in nonlinear behaviour. Due to similarities in the mathematical treatment of nonlinear fibre optics with nonlinear wave interactions in a range of physical systems (e.g. ocean waves), fibre-optic systems provide a convenient, table-top platform for exploring nonlinear physics to provide insight into other scientific disciplines.
Our long-cavity laser is a particularly interesting nonlinear system, where the increased length reduces the coherence (compared to a typical fibre laser) and introduces numerous possible operating regimes. The effect of nonlinearity can also be manipulated with dispersion and power, enabling exploration of these different regimes and study of the system transitioning from a coherent, stable state to a turbulent noisy regime. We have modelled our laser to gain insight into the pulse dynamics and identified localised persistent structures during radiation build-up. Further work to understand the impact of (and to control) these effects will enable the design of more robust lasers and contribute to the understanding of complex nonlinear systems on the limits of stability.