Studies

SUMMARY:  The aim of this thesis is to investigate the coherence properties of extended plasmon polariton states in the strong coupling regime and their application in the FLIM method and in optical sensor technologies. In this work, the influence of the room temperature strong interaction between SPPs and excitons on the fluorescence lifetime and the photobleaching effect has been investigated using TIRE and FLIM. The total internal reflection ellipsometry (TIRE) method was used to investigate the strong interaction between TPPs and SPPs in nanophotonic structures formed from 1D PC and gold nanosphere lattices. The thesis consists of an introduction, literature review, methods, results and conclusions, summary and reference list. FLIM was used for the first time to evaluate the photobleaching effect, and the results showed that the photobleaching effect in plasmonic-excitonic structures in strong interactions was significantly reduced compared to single rhodamine 6G layers. A new way to control and vary the propagation length of hybrid plasmonic excitation at strong couplings between TPP and SPP components using surface arrays has been found. The optical signal sensitivity of the hybrid plasmonic resonances is also compared and obtained much better than that of the conventional surface plasmon resonance (SPR) in a continuous gold layer.

SUMMARY:  Atmospheric black carbon (BC) commonly referred to as soot has significant adverse effects on air quality, climate change, and human health, contributing to issues such as respiratory and cardiovascular diseases as well as reduced cognitive function, both locally and globally. This thesis aims to assess the dynamics of source-apportioned BC mass concentration in urban environments and identify the principal factors influencing these concentrations during the period from September 2020 and May 2022 in Vilnius, the capital and largest city of Lithuania. Such studies are particularly crucial in urban areas, where high population densities face increased exposure to BC emissions from transportation and residential heating, resulting in poor air quality and heightened health risks for residents. This thesis outlines three main research directions: (i) the urban background BC mass concentration sampling campaign; (ii) the investigation of the indoor-outdoor relationship of BC concentrations and their source apportionment; (iii) an analysis of BC deposition on urban trees (Norway spruce and silver birch). The findings reveal that fossil fuel combustion is the predominant BC source in outdoor and indoor air. Mechanical ventilation significantly reduces indoor pollutant concentrations compared to outdoor levels. Local sources were identified as the primary contributors to BC levels, particularly during the heating season. Additionally, all analysed samples of tree leaves and needles contained traces of BC, demonstrating the role of urban greenery in mitigating pollution through its capacity to capture airborne particles.

SUMMARY: This thesis describes studies on the generation of femtosecond pulses in the 1.1–3 µm spectral range (SWIR) by supercontinuum (SC), optical parametric (OPCPA), and stimulated Raman scattering amplifiers (SR), with pumping by picosecond-duration 1030 nm pulses. This work explores the synergy of combining various nonlinear effects to efficiently generate SWIR femtosecond pulses. The first part of the thesis present a mJ-class SWIR OPCPA laser system developed during the study, where the seed source is a broadband SC. In the final stage of the system, an outstanding pump-to-signal conversion efficiency of up to ~25% was achieved, resulting in output pulse energy of ~2.2 mJ. Without active spectral phase control, the pulses were compressed up to ~38 fs. The second part outlines investigated approaches to improve SRS efficiency in the transient regime by extending the pump spectral bandwidth in the NIR region. It was demonstrated transient cascade SRRS combs in compressed hydrogen with an efficiency of up to ~52% covering ~1.1 – 1.4 μm wavelength. Additionally, adjacent vibrational Stokes mode spectral synthesis was achieved in KGW crystals, where the composite spectral bandwidth of the signal increased ~23 times compared to the pump pulses, with a conversion efficiency of ~35%. The third part of the thesis describes studies combining SWIR OPCPA with SRS in KGW crystals and hydrogen. In the first case, energy transfer from signal to idler was demonstrated, achieving a conversion efficiency of ~25%. In the second case, revealed that positively chirped broadband SC seed pulses contribute to the extension of the SRRS spectral bandwidth to longer wavelengths compared to negatively chirped ones.