Single-Photon Level Dispersive Fourier Transform: Ultrasensitive Characterization of Noise-Driven Nonlinear Dynamics

Dispersive Fourier transform is a characterization technique that allows directly extracting an optical spectrum from a time domain signal, thus providing access to real-time characterization of the signal spectrum. However, these techniques suffer from sensitivity and dynamic range limitations, hampering their use for special applications in, e.g., high-contrast characterizations and sensing. Here, we report on a novel approach to dispersive Fourier transform-based characterization using single-photon detectors. In particular, we experimentally develop this approach by leveraging mutual information analysis for signal processing and hold a performance comparison with standard dispersive Fourier transform detection and statistical tools. We apply the comparison to the analysis of noise-driven nonlinear dynamics arising from well-known modulation instability processes. We demonstrate that with this dispersive Fourier transform approach, mutual information metrics allow for successfully gaining insight into the fluctuations associated with modulation instability-induced spectral broadening, providing qualitatively similar signatures compared to ultrafast photodetector-based dispersive Fourier transform but with improved signal quality and spectral resolution (down to 53 pm). The technique presents an intrinsically unlimited dynamic range and is extremely sensitive, with a sensitivity reaching below the femtowatt (typically 4 orders of magnitude better than ultrafast dispersive Fourier transform detection). We show that this method can not only be implemented to gain insight into noise-driven (spontaneous) frequency conversion processes but also be leveraged to characterize incoherent dynamics seeded by weak coherent optical fields

Roadmap on spatiotemporal light fields

Spatiotemporal sculpturing of light pulse with ultimately sophisticated structures represents the holy grail of the human everlasting pursue of ultrafast information transmission and processing as well as ultra-intense energy concentration and extraction. It also holds the key to unlock new extraordinary fundamental physical effects. Traditionally, spatiotemporal light pulses are always treated as spatiotemporally separable wave packet as solution of the Maxwell's equations. In the past decade, however, more generalized forms of spatiotemporally nonseparable solution started to emerge with growing importance for their striking physical effects. This roadmap intends to highlight the recent advances in the creation and control of increasingly complex spatiotemporally sculptured pulses, from spatiotemporally separable to complex nonseparable states, with diverse geometric and topological structures, presenting a bird's eye viewpoint on the zoology of spatiotemporal light fields and the outlook of future trends and open challenges.Comment: This is the version of the article before peer review or editing, as submitted by an author to Journal of Optics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

A comparison of processing techniques for producing prototype injection moulding inserts.

This project involves the investigation of processing techniques for producing low-cost moulding inserts used in the particulate injection moulding (PIM) process. Prototype moulds were made from both additive and subtractive processes as well as a combination of the two. The general motivation for this was to reduce the entry cost of users when considering PIM. PIM cavity inserts were first made by conventional machining from a polymer block using the pocket NC desktop mill. PIM cavity inserts were also made by fused filament deposition modelling using the Tiertime UP plus 3D printer. The injection moulding trials manifested in surface finish and part removal defects. The feedstock was a titanium metal blend which is brittle in comparison to commodity polymers. That in combination with the mesoscale features, small cross-sections and complex geometries were considered the main problems. For both processing methods, fixes were identified and made to test the theory. These consisted of a blended approach that saw a combination of both the additive and subtractive processes being used. The parts produced from the three processing methods are investigated and their respective merits and issues are discussed

Reducing risk in pre-production investigations through undergraduate engineering projects.

This poster is the culmination of final year Bachelor of Engineering Technology (B.Eng.Tech) student projects in 2017 and 2018. The B.Eng.Tech is a level seven qualification that aligns with the Sydney accord for a three-year engineering degree and hence is internationally benchmarked. The enabling mechanism of these projects is the industry connectivity that creates real-world projects and highlights the benefits of the investigation of process at the technologist level. The methodologies we use are basic and transparent, with enough depth of technical knowledge to ensure the industry partners gain from the collaboration process. The process we use minimizes the disconnect between the student and the industry supervisor while maintaining the academic freedom of the student and the commercial sensitivities of the supervisor. The general motivation for this approach is the reduction of the entry cost of the industry to enable consideration of new technologies and thereby reducing risk to core business and shareholder profits. The poster presents several images and interpretive dialogue to explain the positive and negative aspects of the student process

Single-shot femtosecond laser ablation of nano/polycrystalline titanium investigated using molecular dynamics and experiments

Laser ablation, a crucial technique in various scientific and industrial fields, plays a pivotal role in precision manufacturing. Industries such as aerospace rely on laser technology for tasks like drilling microscale holes in jet turbine components to enhance air-cooling efficiency. Moreover, laser-based material processing is indispensable in addressing healthcare challenges with facilitating the postprocessing of 3D-printed bespoke components like patient-specific implants as an example. Ultrashort pulsed laser ablation enables precise micro and nanofabrication, enhancing material properties like wettability, adhesion and biocompatibility. This is particularly important in medical applications like implant development, as it can help reduce the possibility of post-surgery infections. Scientifically, understanding the intricacies of ultrashort pulsed laser ablation contributes to ongoing research and development efforts in ablation technology, fostering the enhancement of new material properties related to surface modifications. Additionally, laser ablation plays a crucial role in additive manufacturing technology like 3D printing of metals by facilitating the post-processing stage. This thesis investigates the ultrashort pulsed laser ablation of titanium, utilising a combination of molecular dynamics simulations and experiments. Molecular dynamics simulations are used for their capability to model systems at the atomistic scale and ultrashort timescale (femtoseconds in this work), in contrast to the finite element method, and for their computational efficiency compared to methods employing more detailed calculations like density functional theory. The primary focus of this work is on exploring the size effect by examining variations in beam spot diameter and grain size with profound implications for ultraprecision manufacturing of titanium surfaces in sub-micron length scale, produced by casting and additive manufacturing techniques. It contributes a nuanced understanding of ultrashort pulsed laser ablation by bridging the gap between molecular dynamics simulations and experiments. It extends the boundaries by simulating the largest feasible atomistic models and measuring features at the smallest scale permitted by the available metrology devices in experiments. The key observations showed the critical importance of the beam spot diameter in determining the laser fluence necessary to achieve average plasma temperatures of around 9,000 K, as well as a direct correlation between the grain size and the response of the material to laser irradiation. Notably, the simulations indicated that the 10 nm laser beam spot diameter compared to the 25 nm requires 59% more absorbed laser energy for ablation. Furthermore, the investigation revealed that by increasing the grain size in alpha-phase titanium, when the number of grains in the volume of 500,000 nm³ were reduce from 500 grains to 10, 36% more absorbed laser fluence was necessary to achieve average plasma temperatures of approximately 9,000 K, despite the material exhibiting higher heat conductivity. Additionally, a comparative analysis of ultrashort pulsed laser ablation between atomistic models of pure titanium with single crystal and polycrystalline structures were carried out using molecular dynamics simulations. The results revealed that the nanocrystalline sample modelled in this work, which exhibited lower heat conduction, produced a relatively deeper crater compared to its single crystal counterpart. The single crystal sample had a greater resistance to ablation, leading to the formation of a recast layer with rougher edges in contrast to the nanocrystalline sample. In materials science and engineering "size effect" is attributed to a phenomenon where the mechanical, thermal, optical or electrical properties of a crystalline material changes as a function of its physical size where at least one dimension is in submicron length scale. Experimental examination of the size effect was carried out on commercially pure titanium (consisting of 99.6% titanium and the remaining 0.4% containing carbon, nitrogen, hydrogen, iron and oxygen atoms) and Ti-6Al-4V alloy where craters were formed on both materials using single-shots with identical fluence while varying the diameter of the laser beam. It was observed that reducing the beam spot diameter resulted in relatively shallower craters, suggesting an increased threshold for ablation. Experiments comparing single-shot laser ablation outcomes between casted and 3D-printed Ti-6Al-4V alloy revealed that the 3D-printed surface (\u1d445\u1d44e = 32 \u1d45b\u1d45a) produced a slightly cleaner crater and smoother recast layer compared to the casted material (\u1d445\u1d44e = 45 \u1d45b\u1d45a). This observation was made after subjecting both substrates to ultrashort pulsed laser irradiation with identical laser parameters

Roadmap on structured light

Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized

Light-triggered unidirectional molecular rotors: theoretical investigations on conformational dynamics and laser control

Two light-triggered molecular motors based on chiral overcrowded alkenes have been studied in the electronic ground state: a second-generation motor (2) and a redesigned motor (3). A semiempirical Monte-Carlo-type of conformational search has been implemented to find local minima in the ground state PESs of 2 and 3, which then have been reoptimized by ab-initio calculations. While in 3 only the four isomers of the rotary cycle are found, new isomers have been found in the case of 2, leading to different reaction pathways for the thermal helix-inversion. TSs for all the possible thermal conversions have been also computed. The obtained E_a values are in excellent agreement with those reported in the literature. The simple model BCH (core unit of many motors) has been studied from a quantum chemical and quantum dynamical point of view. The controversial nature of BCH's electronic transitions has been investigated using high-level ab-initio multiconfigurational and perturbational methods, including the development of a basis set specific to the problem at hand. The first two excited states of Bu-symmetry ((pi,3s)-Rydberg and (pi,pi*), respectively) are resolved at the MS-CASPT2-level of theory, providing vertical transition energies and oscillator strengths matching the experimental values. In addition, the origin of the (p,p*)-band is computed, yielding an energy value well below the FC-value of the (pi,3s_R)-maximum, explaining this band's unexpected intensity. Finally, a one-dimensional PES along BCH's torsional coordinate has been computed at the MS-CASPT2-level of theory, and quantum dynamical simulations have been carried out. These have focused on the obtainment of control laser fields that are able to trigger unidirectionality even in the symmetric PES (as opposed to 2 and 3 system). Optimal control strategies as well as the intuitive IR+UV-scheme both succeeded in achieving sustained, unidirectional torsional motion of BCH in the excited state