Our Research
Here you’ll find more details on our work as well as a summary of principal research efforts and projects.
Electric Field Induced Second Harmonic (EFISH) Generation
The electric field strength (along with the electron density) is perhaps the most fundamental quantity governing plasma physics. It serves as the initial conditions, based on a given geometry (or boundary) responsible for determining how the plasma (chemistry) responds. Yet quantifying this parameter directly, and accurately, is one the most challenging experimental tasks. EFISH is a (mostly) non-intrusive, laser-based method that has shown tremendous promise for probing electric field strengths, particularly in non-equilibrium plasmas. Some of its key advantages include its excellent (sub-ns) time resolution, compatibility with almost all gas mixtures, field vector sensitivity, and most importantly, its ease of implementation. Our group is focused on formulating a rigorous characterization of the EFISH signal, using a variety of approaches (such as machine-learning) and applying this diagnostic to various plasma-based applications and environments.
Team members: Yang Zhijian, Edwin Setiadi Sugeng, Zhang Yaqi (visiting PhD student from XJTU, PRC), Becky Yang (visiting PhD student from PolyU, HK)
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PLEET is an optical, molecular tagging method for measuring velocities in air or nitrogen-containing gases. By photodissociating molecular nitrogen, and taking advantage of the long-lived fluorescence arising from atomic recombination, the displacement of ‘laser-induced lines’ can be tracked in time to infer the flow velocity. This technique is particularly well-suited for interrogating high-speed (supersonic) flows where there is a relative scarcity of competing technologies. Our current work focuses on using picosecond duration laser pulses in the ultraviolet (UV) for driving the photodissociation process.
Team members: Xiao Hongxun, Wu Huimin (visiting from HUST, PRC)
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This project evaluates the effectiveness of non-equilibrium plasmas as an efficient means of sustaining a lean flame. The idea behind burning lean (i.e., less fuel) is not only to reduce consumption, but also to lower the flame temperature. The latter in turn suppresses the production of oxides of nitrogen (NOx), a major air pollutant which observes a well-known exponential dependence on temperature (also known as thermal NOx). Unfortunately, many fuels when burnt lean result in an unstable flame, which can negatively impact combustion performance. This is where we hope plasmas can help. While the prognosis for lean flame stabilization has generally been good, an important research obstacle is that the plasma tends to introduce its own NOx.
The longer term goal is to develop a combustor that can function reliably via plasma-assisted technology. Such work is of great relevance to the development of micro-turbines where thermal management is an enduring problem.
Team members: Edwin Setiadi Sugeng, Zong Yichen (collaborator from CARES)
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One of the obstacles facing optical methods when used as a near-wall velocity probe, is signal interference from intense background scattering or reflection, or the lack of particles close to a solid boundary. FRS is a ‘seedless’, laser-based method which has been widely utilized for optical thermometry. By relying on a narrowband molecular gas filter (such as iodine vapour) to spatially reject the unwanted wall reflection/scattering, the Doppler-broadened (scattered) signal is still partially retained and captured. In this project, we examine FRS as a tool for velocimetry, instead measuring the Doppler-shifted scattering due to motion of the bulk flow. The goal is to quantify the near-wall capabilities of FRS, especially in high-speed flows, with a view to using it for shear stress quantification.
Team members: Wu Huimin, Xiao Hongxun, Huang Xin (collaborator from T-Labs NUS)