Dun Liu

Bio: Dun Liu is an academic researcher from University of Liverpool. The author has contributed to research in topics: Laser & Spatial light modulator. The author has an hindex of 11, co-authored 28 publications receiving 620 citations. Previous affiliations of Dun Liu include Hubei University of Technology.

A review of ultrafast laser materials micromachining

Abstract: A brief review is given regarding ultrafast laser micromachining of materials. Some general experimental observations are first provided to show the characteristics of ultrafast laser micromachining. Apart from empirical research, mathematical models also appear to allow for a further and systematic understanding of these phenomena. A few fundamental ultrafast laser micromachining mechanisms are addressed in an attempt to highlight the physics behind the experimental observations and the mathematical models. It is supposed that a vivid view of ultrafast laser micromachining has been presented by linking experimental observations, mathematical models and the behind physics.

High-speed uniform parallel 3D refractive index micro-structuring of poly(methyl methacrylate) for volume phase gratings

Abstract: Parallel femtosecond refractive index laser inscription of clinical grade poly(methyl methacrylate) (PMMA) at 775 nm, 170 fs pulselength is demonstrated with multiple low fluence beams generated with the aid of a spatial light modulator. Using optimised computer-generated holograms (CGHs), 16 diffracted near identical beams were focused simultaneously within bulk PMMA to create a series of 19 μm pitch, 5 mm×5 mm×1–4 mm thick volume phase gratings at high speed. First order diffraction efficiency rises with grating thickness in accord with diffraction theory, reaching 75% at the first Bragg angle (4 mm thick) with fabrication time around 1 hour. By carefully stitching filamentary modifications while eliminating effects such as pulse front tilt during inscription, gratings exhibit high uniformity, which has not been achieved previously using femtosecond inscription. Highly uniform modification is exhibited throughout the material consistent with the observed excellent angular selectivity and low background scatter and quantitative comparison with first order diffraction theory is satisfactory. The diffraction efficiency and hence refractive index profile shows a temporal behaviour related to the material response after exposure. Simultaneous 3D modification at different depths is also demonstrated, highlighting the potential of creating complex 3D integrated optical circuits at high speed through the application of CGHs.

Solution processed organic thermoelectrics: towards flexible thermoelectric modules

Abstract: Organic semiconductor materials have advantages of low cost, light weight, mechanical flexibility and low-temperature solution processability over large areas, enabling the development of personal, portable, and flexible thermal modules. This review article summarizes the recent progress made in the area of organic thermoelectrics (TEs), including organic molecular structures, devices, characterization methods, and approaches to improve the performance. We begin with the discussion of each TE parameter and particularly their correlations in organic TEs. Then the TE applications of molecular organic semiconductors, poly(3,4-ethylenedioxythiophene), polymer nanostructures and molecular junctions are reviewed. Next we turn to highlight the nanocomposites of polymers and carbon nanotubes or nanocrystals, which lead to enhanced TEs. Interestingly, the merging of TEs and photovoltaics offers a new direction towards a great capability of electric energy output. Critical challenges of organic TE materials include stability, sample preparation and measurement techniques, which are also discussed. Finally, the relationships among organic semiconductor structures, hybrid composites, doping states, film morphology and TE performance are revealed, and a viable avenue is envisioned for synergistic optimization of organic TEs.

A review of ultrafast laser materials micromachining

Abstract: A brief review is given regarding ultrafast laser micromachining of materials. Some general experimental observations are first provided to show the characteristics of ultrafast laser micromachining. Apart from empirical research, mathematical models also appear to allow for a further and systematic understanding of these phenomena. A few fundamental ultrafast laser micromachining mechanisms are addressed in an attempt to highlight the physics behind the experimental observations and the mathematical models. It is supposed that a vivid view of ultrafast laser micromachining has been presented by linking experimental observations, mathematical models and the behind physics.

Fabrication of Micro/Nano Structures on Metals by Femtosecond Laser Micromachining

Abstract: Femtosecond laser micromachining has emerged in recent years as a new technique for micro/nano structure fabrication because of its applicability to virtually all kinds of materials in an easy one-step process that is scalable. In the past, much research on femtosecond laser micromachining was carried out to understand the complex ablation mechanism, whereas recent works are mostly concerned with the fabrication of surface structures because of their numerous possible applications. The state-of-the-art knowledge on the fabrication of these structures on metals with direct femtosecond laser micromachining is reviewed in this article. The effect of various parameters, such as fluence, number of pulses, laser beam polarization, wavelength, incident angle, scan velocity, number of scans, and environment, on the formation of different structures is discussed in detail wherever possible. Furthermore, a guideline for surface structures optimization is provided. The authors’ experimental work on laser-inscribed regular pattern fabrication is presented to give a complete picture of micromachining processes. Finally, possible applications of laser-machined surface structures in different fields are briefly reviewed.

Strong-field physics with singular light beams

Abstract: Optical vortices exhibit a corkscrew-like shape as they travel. The study of this phenomenon, known as singular optics, is now extended to the high-power regime where high-harmonic processes become evident. This type of radiation could help illuminate novel attosecond phenomena in atoms and molecules.