DMFT and GW meet THz spectroscopy: ultra-fast THz pump-probe spectroscopy and many-body physics, a joint UK-Switzerland-China collaboration. 

The terahertz (THz) region of the electromagnetic spectrum, referring roughly to the frequencies from 100 GHz or 0.1 THz to 30 THz is the bridge between the microwave and infrared spectral bands. In the last two decades there has been extensive progress in the development of THz technology. This progress has enabled a multitude of potential applications, be it communications, biomedical applications, imaging, homeland security, quality control of food and agricultural products, matter and light control, or working as pump and/or probe to develop novel advanced materials, – in every application it has emerged as one of the most promising areas of interest.  In this work, we will use numerical techniques to design organic crystals to be fabricated and commercialized by the industrial partner.

The proposed project aims at designing crystals, by guidance from first-principle calculations, to generate radiation in the 5-15 THz range. The motivation is twofold. First, from the industrial applications, it is required to increase the imaging and spectroscopic resolution. So far, most industrial spectrometers depend on low frequency < 3 THz. Having a source crystal to efficiently generate terahertz in the 5-15 THz will lead to shorter time and spatial feature size thus increasing the resolution. One example is car painting layer thickness. Car painting is usually made of several thin layers where the thickness of each is critical for proper protection of the car frame. Terahertz reflections at the interfaces between the layers allow for accurate determination of the thickness. So far, the present sources generate low frequency long pulses that make it difficult to distinguish between different reflections. 5-15 THz source should solve this problem.

From the basic research point of view, nonlinear THz spectroscopy rose toprominence in the past few years thanks to the rapid development of intense laser-based sources. Terahertz excitation combines both selective and non-thermal control thus providing a versatile tool to coherently control matter on the ultrafast time scale. That is being presently matched with the X-ray free electron laser probe pulses with atomic and femtosecond length and time scales. SLAC (USA), European XFEL (Germany), and the SwissFEL (Switzerland) are a good example where THz pump X-ray probe schemes are under extensive planning. However, intense THz source technology has, so far, been limited to the sub-5 THz range leaving the 5-15 THz as the last remaining gap in the electromagnetic spectrum where the technology is lagging.

The project will involve using DFT and its extensions, DFT+DMFT, GW, to design new THz crystals, by using existing technologies and push the existing state-of-the-art, to describe interactions of THz radiations with many-body electronic states. It is a very multidisciplinary project that brings together ab initio molecular calculations, laser physics and technology, organic chemistry and crystal growth for a well-defined application in physics and chemistry. The major objectives of the project are to establish a new platform (methodology) for intense THz system development and to close the remaining electromagnetic (THz) spectral gap with a library of organic molecules (crystals) that could fit different applications. The project is co-funded by SwissTHz, a Swiss based research institution, and will involve link with Beijing Normal University. The industrial partner will take care (with its collaborators) of the fabrication of the crystals testing them on laser systems.  

The PhD is a 3.5-4y positions based at King's College London. Candidates must be EU/UK citizens and hold a Masters in Physics or Chemistry. The project will involve a combination of theory and software developments, numerical analysis, analytical calculations, simulations. Scientific visits to Beijing and Switzerland are envisaged as part of this project, albeit not an absolute requirement. For any queries, contact : [email protected].