Spatiotemporal probing and control of nonlinear optical phenomena in 2D materials using unconventional states of polarization (ARTEMIS)

The first year of my doctoral studies deals with the learning and acquiring of the necessary experimental skills needed to accomplish the proposed research. For example, I received training on the use of several laser systems (e.g. Chameleon and OPO laser system, picosecond laser system, and continuous wave laser systems), instruments (e.g., spatial light modulators, liquid-crytals-based polarization mode converters and EMCCD) and specialized optical techniques (e.g., spectroscopy, nonlinear optical microscopy and beam engineering). I have already completed 25 credits out of the 25 mandatory credits on Field specific studies in physics at Tampere University. I attended NANOP 2023 conference, which was dedicated for nanophotonics where I got an opportunity to learn cutting edge research going on in the field. I have also presented a poster representing my group’s work on Markus Pessa Summer School, at Tampere University. During this time, I have also collaborated with Hybrid Solar Cells (HSC) group in Tampere university for the nonlinear measurement of perovskite inspired materials. These experiences including the capacity to work in highly multidisciplinary research environments contributed well to my growth and professional competence as an early career researcher. In the following, I will be giving summaries of the research works where I have been involved and are linked to my research proposal.

Topic 1. Direct mapping of coupling effects in a semiconductor nanopillar and gold film heterostructure using 3D multimodal nonlinear optical microscopy.

This work was done in collaboration with the ORC at TAU. The objective was to investigate the complex interaction within semiconductor nanopillar and gold film heterostructures using 3D multimodal nonlinear optical microscopy. Focused on second- and third-harmonic generation (SHG and THG) signal mapping, we explore the complex coupling effects at the nanoscale. We could directly observe coupling between the gold film and semiconductor heterostructure by systematically studying the nonlinear optical response and comparing their 2D ratiometric maps. This work reveals the vital interplay between semiconductor excitons and metal plasmons, showing their potential in enhancing nonlinear optical phenomena.
Citation: R. Varghese et al., manuscript in preparation

Topic 2. Orbital angular momentum-induced nonlinear emission from a monolayer graphene
This work was done in collaboration with the Nanophotonics Group at Aalto University. This is currently progressing with the analysis and optimization of new nonlinear microscope for imaging structured light-matter interactions at the nanoscale. There has been preliminary examination for the working of the setup to study the role of spin-orbit coupling phenomena in manipulating NLO responses from monolayer graphene. An OAM beam of topological charge 1 is being compared with a gaussian beam for the nonlinear response from the graphene sample. Initially we have investigated a graphene sample in Si/SiO2 substrate but to avoid background or the substrate noise the collaborators have later provided the graphene sample in cover glass. The data obtained are planned to be included in an upcoming manuscript, where the role of spin-orbit coupling phenomena in manipulating NLO responses is investigated.

Citation: Y. Tamashevich et al., manuscript in preparation

Current stage and Future planning

I am presently strengthening my research skills by being involved in specialized research activities of the Photonics Laboratory. These topics have links to my research proposal. These are listed below:
1. Nonlinear optical characterization and microscopy of 2D semiconductor materials from our collaborators at Aalto University.
2. Structuring light by realizing ENZ modes in Fabry-Perot cavities with 2D materials to study Raman amplification.

For the second-year, one or two papers based on the topics above is planned to be submitted or published. I also plan to attend international conferences that are related to my present research to present, seek potential collaborations, and receive guidance vital to the progression of my work.

Riya Varghese, a PHD student at the Nonlinear Optics (NLO) Group of the Photonics Laboratory at Tampere University, received a 24000€ grant from Finnish Foundation for Technology Promotion, the funding period was 01.06.2023 – 31.05.2024 .