15 research outputs found
Surfactant-aided exfoliation of molydenum disulphide for ultrafast pulse generation through edge-state saturable absorption
We use liquid phase exfoliation to produce dispersions of molybdenum
disulphide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical
structures of the bile salt surfactants play a crucial role in the exfoliation
and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched
in single and few (<6) layer flakes with large edge to surface area ratio. We
use the dispersions to fabricate free-standing polymer composite wide-band
saturable absorbers to develop mode-locked and Q- switched fibre lasers,
tunable from 1535-1565 and 1030-1070 nm, respectively. We attribute this
sub-bandgap optical absorption and its nonlinear saturation behaviour to
edge-mediated states introduced within the material band-gap of the exfoliated
MoS2 nanoflakes.Comment: 6 pages, 5 figure
Towards Intense Ultra-Broadband High Repetition Rate Terahertz Sources Based on Organic Crystals [Invited]
Increasing the average power of broadband, few-cycle terahertz (THz) sources
is currently a topic of intense investigation, fueled by recent immense
progress in high average power femtosecond laser driving sources at 1030 nm.
However, many crucial applications would benefit not only from an increase in
average power, but also from ultra-broad bandwidth, while maintaining high
dynamic range at these frequencies. This calls for the challenging combination
of high repetition rates and high average power simultaneously. Here, we
discuss the recent progress in the promising approach enabled by organic
crystals for THz-generation. Specifically, this review article discusses
advances with the most commonly used organic crystals BNA, DAST, DSTMS, OH1 and
HMQ-TMS. We place special emphasis on nonlinear and thermal properties and
discuss future directions for this field
MHz-repetition-rate, sub-mW, multi-octave THz wave generation in HMQ-TMS
We demonstrate the first megahertz (MHz) repetition-rate, broadband terahertz (THz) source based on optical rectification in the organic crystal HMQ-TMS driven by a femtosecond Yb:fibre laser. Pumping at 1035 nm with 30 fs pulses, we achieve few-cycle THz emission with a smooth multi-octave spectrum that extends up to 6 THz at -30 dB, with conversion efficiencies reaching 10-4 and an average output power of up to 0.38 mW. We assess the thermal damage limit of the crystal and conclude a maximum fluence of ∼1.8 mJ·cm-2 at 10 MHz with a 1/e2 pump beam diameter of 0.10 mm. We compare the performance of HMQ-TMS with the prototypical inorganic crystal gallium phosphide (GaP), yielding a tenfold electric field increase with a peak on-axis field strength of 7 kV·cm-1 and almost double the THz bandwidth. Our results further demonstrate the suitability of organic crystals in combination with fibre lasers for repetition-rate scaling of broadband, high-power THz sources for time-domain spectroscopic applications
Advancements in Mode-Locked Fibre Lasers and Fibre Supercontinua
The temporal characteristics and the spectral content of light can be manipulated and
modified by harnessing linear and nonlinear interactions with a dielectric medium. Optical
fibres provide an environment in which the tight confinement of light over long distances
allows the efficient exploitation of weak nonlinear effects. This has facilitated the
rapid development of high-power fibre laser sources across a broad spectrum of wavelengths,
with a diverse range of temporal formats, that have established a position of
dominance in the global laser market. However, demand for increasingly flexible light
sources is driving research towards novel technologies and an improved understanding
of the physical mechanisms and limitations of existing approaches.
This thesis reports a series of experiments exploring two topical areas of ongoing research
in the field of nonlinear fibre optics: mode-locked fibre lasers and fibre-based
supercontinuum light sources.
Firstly, integration of novel nano-materials with existing and emerging fibre-based
gain media allows the demonstration of ultrafast mode-locked laser sources across the
near-infrared in a conceptually simple, robust, and compact scheme. Extension to important
regions of the visible is demonstrated using nonlinear conversion.
Scaling of pulse energies in mode-locked lasers can be achieved by operating with
purely positive dispersion for the generation of chirped pulses. It is shown unequivocally,
through a direct measurement, that the pulses generated in ultra-longmode-locked lasers
can exist as highly-chirped dissipative soliton solutions of the cubic (and cubic-quintic)
Ginzburg Landau equation. The development of a numerical model provides a framework
for the interpretation of experimental observations and exposes unique evolution
dynamics in extreme parameter ranges. However, the practical limitations of the approach
are revealed and alternative routes towards achieving higher-energy are proposed.
Finally, an experimental and numerical study of the dependence of continuous-wave
pumped supercontinua on the coherence properties of the pump source shows an optimum
exists that can be expressed as a function of the modulation instability period. A
new and simplified model representing the temporal fluctuations expressed by continuous wave
lasers is proposed for use in simulations of supercontinua evolving from noise.
The implications of the experiments described in this thesis are summarised within
the broader context of a continued research effort
Advancements in mode-locked fibre lasers and fibre supercontinua
The temporal characteristics and the spectral content of light can be manipulated and modified by harnessing linear and nonlinear interactions with a dielectric medium. Optical fibres provide an environment in which the tight confinement of light over long distances allows the efficient exploitation of weak nonlinear effects. This has facilitated the rapid development of high-power fibre laser sources across a broad spectrum of wavelengths, with a diverse range of temporal formats, that have established a position of dominance in the global laser market. However, demand for increasingly flexible light sources is driving research towards novel technologies and an improved understanding of the physical mechanisms and limitations of existing approaches. This thesis reports a series of experiments exploring two topical areas of ongoing research in the field of nonlinear fibre optics: mode-locked fibre lasers and fibre-based supercontinuum light sources. Firstly, integration of novel nano-materials with existing and emerging fibre-based gain media allows the demonstration of ultrafast mode-locked laser sources across the near-infrared in a conceptually simple, robust, and compact scheme. Extension to important regions of the visible is demonstrated using nonlinear conversion. Scaling of pulse energies in mode-locked lasers can be achieved by operating with purely positive dispersion for the generation of chirped pulses. It is shown unequivocally, through a direct measurement, that the pulses generated in ultra-longmode-locked lasers can exist as highly-chirped dissipative soliton solutions of the cubic (and cubic-quintic) Ginzburg Landau equation. The development of a numerical model provides a framework for the interpretation of experimental observations and exposes unique evolution dynamics in extreme parameter ranges. However, the practical limitations of the approach are revealed and alternative routes towards achieving higher-energy are proposed. Finally, an experimental and numerical study of the dependence of continuous-wave pumped supercontinua on the coherence properties of the pump source shows an optimum exists that can be expressed as a function of the modulation instability period. A new and simplified model representing the temporal fluctuations expressed by continuous wave lasers is proposed for use in simulations of supercontinua evolving from noise. The implications of the experiments described in this thesis are summarised within the broader context of a continued research effort.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
2D Saturable Absorbers for Fibre Lasers
Two-dimensional (2D) nanomaterials are an emergent and promising platform for future photonic and optoelectronic applications. Here, we review recent progress demonstrating the application of 2D nanomaterials as versatile, wideband saturable absorbers for Q-switching and mode-locking fibre lasers. We focus specifically on the family of few-layer transition metal dichalcogenides, including MoS2, MoSe2 and WS2
Secondary reinforcement and number of primary reinforcements
Pigeons' pecks on either of two concurrently available response keys produced secondary reinforcers according to independent one-minute variable-interval schedules. Different secondary reinforcers, in the presence of which the rates of primary reinforcement were equal, were associated with each key. The rate of pecking maintained by each secondary reinforcer varied directly, but nonproportionally, with the number of primary reinforcements given in the presence of the secondary reinforcer