This 12 month period has taken the foundation established in the 1st year activity, based on material characterisation on WP1 and theoretical developments on WP2, to investigate the nonlinear properties of these 2D materials in WP3 and WP4. Importantly, we show the first nonlinear optical signatures from the two targeted approaches - the up-conversion using DMs (WP3) and the down conversion of optical light using TMDs (WP4).
Overview and Highlights
1) Continual improvements in growth (WP1) with the optimisation of TIs and QCLs that are being fed into WP3 and WP4
2) A range of Electronic devices have been processed realised to control the researched nonlinearties. This extends from gate controlled DM (Graphene and TIs) to TMD devices with applied electric fields, as well as the use of resonators to enhance light-matter interactions. (WP1)
3) Theoretical developments with a strong emphasis on the calculations of 2D bandstructures of TMDs, the exciton spectrum and their linear and nonlinear properties. Approach adapted to all TMDs permitting a tool to design TMDs for down-conversion using applied fields and the material environment; Further the thermodynamic model for HHG has been adapted for excitation at high frequencies (WP2).
4) Optimised design and realization of resonators to enhance the power density for THz light-matter interaction with integrated DMs and TMDs (WP1, WP3 and WP4).
5) Harmonic generation (HG) using high field system demonstrated in DMs (TIs and graphene) (WP3). We have demonstrated HG in a range of materials, from graphene and TIs, as well as gate controlled graphene.
6) HG from a graphene layer pumped by a high power THz QCL (WP3). This work has shown that the generation of light at 9 THz with a QCL pump at 3 THz, using a graphene layer coupled to a THz resonator.
7) Demonstration of THz gain in MoS2 (WP4). Continuing from measurements for the 1st year report showing enhanced THz emission, here we have shown the presence of large band THz gain through careful measurements of THz transmission to exclude an impedance matching effect.
8) Layer controlled down-conversion in the TMDs MoSe2, PtSe2 and Ferromagnetic/PtSe2 heterostructures using optical pumps (WP4). Using optical pumps, down-conversion has been demonstrated in a range of TMDs structures. Further the down-converted light is shown to be carefully controlled by number of the atomic layers.
9) Saturable absorption of TMDs in the MIR (WP4). Using a tuneable OPA, we have demonstrated a saturable absorption in PtSe2 layers and highlight the low power requirements when pumping with MIR light, making it compatible for pumping with QCLs
10) Proof of principle investigations have shown how near-field spectroscopy can be used to study the dispersion in TIs and show the role of surface states. Further a metrological grade spectrometer has been realised for future EXTREME-IR sources (WP5)
11) Several scientific papers on EXTREME-IR advances published in high impact journals (e.g. Nature satellite journals and Wiley Infomat) and further are in progress.
12) Recruitment of postdoctoral and doctoral researchers at all partner’s site.
These second year highlights provide the potential of realising nonlinear 2D devices, pumped by QCLs and optical lasers, in the EXTREME-IR programme. Progress has been made over a variety of domains, covering materials, optoelectronic devices, cavities and resonators, theoretical nonlinearities, as well as the demonstrations of a range of nonlinearities (up-conversion, down-conversion, saturable absorption and THz amplification). This will be applied to further improvements in nonlinear FIR generation and integration, and fed into exemplar applications in WP5, that are currently being developed.
