Electromagnetic radiation in the frequency range between about 100 GHz and 5 THz can be used for spectroscopy and microscopy, but it is also promising for security screening and even wireless communication. In the present thesis a planar photoconducting large-area THz radiation source is presented. The device exhibits outstanding properties, in particular high THz field strength and generation efficiency and large spectral bandwidth with short THz pulse length. The THz emission is based on acceleration and deceleration of photoexcited carriers in semiconductor substrates. A metallic interdigitated structure at the surface of semi-insulating GaAs provides the electrodes of an Auston switch. In a biased structure photoexcited charge carriers are accelerated. Hence electromagnetic waves are emitted. An appropriately structured second metallization, electrically isolated from the electrodes, prevents destructive interference of the emitted waves. The structure investigated here combines several advantages of different conventional photoconducting THz sources. First, it provides high electric acceleration fields at moderate voltages owing to the small electrode separation. Second, the large active area in the mm2 range allows excitation by large optical powers of some mW. Optical excitation with near-infrared femtosecond lasers is possible with repetition rates in the GHz range. The presented results point out the excellent characteristics regarding the emitted THz field strength, average power, spectral properties, and easy handling of the interdigitated structure in comparison to various conventional emitter structures. Various modifications of the semiconductor substrate and the optimum excitation conditions were investigated. In the second part of this thesis the dynamic conductivity of GaAs/AlxGa1-xAs superlattices in an applied static electric field was investigated with time-resolved THz spectroscopy. The original goal was to explore whether the predicted effect of gain of electromagnetic radiation at THz frequencies is present in such structures. Superlattice samples were grown according to the experimental requirements, which include high specific resistance and sufficient THz transparency. The characterization of the superlattices by Fourier transform infrared spectroscopy and photoluminescence spectroscopy confirms the pronounced miniband properties of the bandstructure. Furthermore indications of Bloch oscillations were found by transport measurements. However, we could not measure a change of the dynamic conductivity when the electric field was toggled. Specific reasons for this and related experiments of other groups are discussed. / Elektromagnetische Strahlung im Frequenzbereich zwischen etwa 100 GHz und 5 THz wird für verschiedene Anwendungen wie Spektroskopie und Mikroskopie genutzt, kann aber auch für Sicherheitstechnik oder sogar Datenübertragung interessant sein. In der hier vorgestellten Forschungsarbeit wird eine großflächige fotoleitende THz-Strahlungsquelle beschrieben, die sich durch eine große THz-Feldstärke und große spektrale Bandbreite auszeichnet. Die THz-Emission basiert auf der Beschleunigung und Verzögerung fotogenerierter Ladungen in Halbleitersubstraten. Eine metallische Interdigitalstruktur auf der Oberfläche von semi-isolierendem GaAs bildet die Elektroden eines Fotoschalters. Ist an diese Struktur eine Spannung angeschlossen, werden optisch generierte Ladungsträger beschleunigt und strahlen elektromagnetische Wellen ab. Eine geeignet strukturierte und isolierte zweite Metallisierung verhindert destruktive Interferenzen der abgestrahlten Wellen. Die vorgeschlagene Struktur vereinigt dabei die Vorteile verschiedener herkömmlicher fotoleitender THz-Quellen. Einerseits ermöglicht der kleine Elektrodenabstand große elektrische Felder zur Beschleunigung fotogenerierter Ladungen schon bei moderaten Spannungen. Andererseits kann die große aktive Fläche von einigen mm2 mit großen optischen Leistungen im Bereich einiger mW angeregt werden. Die optische Anregung mit Nahinfrarot-Femtosekunden- Lasern kann mit Wiederholraten bis in den GHz-Bereich geschehen. Bedingt durch die Eigenschaften der Anregungspulse entstehen kurze spektral breite THz-Pulse. Die vorliegenden Ergebnisse verdeutlichen die hervorragenden Eigenschaften der Interdigitalstruktur im Vergleich zu verschiedenen herkömmlichen Geometrien bezüglich der Feldstärke der abgestrahlten Wellen, der mittleren Leistung und der spektralen Eigenschaften. Dabei ist die Struktur sehr einfach zu handhaben. Es wurden verschiedene Modifikationen des Substrates und die optimalen Bedingungen der optischen Anregung untersucht. Der zweite Teil dieser Arbeit behandelt die Erforschung der dynamische Leitfähigkeit von GaAs/AlxGa1-xAs-Übergittern in Abhängigkeit von einem elektrischen Feld mit Hilfe der zeitaufgelösten THz-Spektroskopie. Es sollte geklärt werden, ob der vorhergesagte Effekt der Verstärkung elektro-magnetischer Strahlung in solchen Strukturen möglich ist. Dazu wurden Übergitterproben gemäß den experimentellen Anforderungen hergestellt. Zu den Vorgaben gehört ein hoher spezifischer Widerstand und ausreichende Transparenz im THz-Bereich. Die Charakterisierung der Übergitter mit Fotolumineszenz- und Fourier-Transformations-IR-Spektroskopie bestätigte die ausgeprägten Minibandeigenschaften der Bandstruktur. Hinweise auf Bloch-Oszillationen wurden durch Ladungstransportmessungen gefunden. Dennoch war eine Änderung der dynamischen Leitfähigkeit beim Schalten des elektrischen Feldes nicht messbar. Gründe dafür und ähnliche Experimente anderer Gruppen werden diskutiert.

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Analytical method validation is the process of establishing that an analytical technique is applicable for a proposed objective. Early in the method development of a new analytical technique an understanding of the instrumental components and procedures is elaborated through scientifically based optimization. The optimization experiments are used to define the operational parameters that yield the maximum performance by the analytical technique for the target analyte before commencing validation studies. This dissertation details method development through experimental investigations instrumental components of LEMS (substrate, laser parameters, and electrospray source conditions). Each instrumental component has a number of induvial parameters which are optimized to yield the maximum laser electrospray mass spectrometry (LEMS) signal intensity for a given analytical problem. LEMS uses a nonresonant, femtosecond (fs) laser to ablate analytes from a surface. Those ablated analytes are then captured by a perpendicular electrospray, ionized, and desolvated to produce ions which travel into the inlet of the mass spectrometer for analysis. Each element of the LEMS experimental setup works in a complementary fashion to generate a mass spectral signal which have specific optimization steps that can dramatically impact the data that can be acquired. The results of the optimization for each instrumental component will then be applied to preliminary method development experiments for the analysis of pharmaceutical compounds from complex formulations biomarker discovery for mice afflicted with a traumatic brain injury.The effect of the laser pulse duration on the ablation mechanism and amount of laser induced conformational changes of aqueous myoglobin was investigated using 55 fs, 56 picosecond (ps), and 10 nanosecond (ns) pulses and laser pulse energies from 0.05 to 1.6 mJ. It was found that the optical properties of the substrates (stainless-steel and quartz) and laser intensity regimes accessible by each pulse duration determined the amount of myoglobin ablated and subsequent mass spectral signal intensity. Laser ablation of myoglobin from both substrates using all laser pulse energies was observed for the 55 fs pulse while the 10 ns pulse required minimum pulse energies of 0.4 and 1.2 mJ for ablation of myoglobin to occur from stainless-steel and quartz, respectively. As the pulse duration increases, thermal processes increase which dictated the relative amount of protein unfolding, number of phosphate adducts, and degree of solvent adduction. Many of the common laser electrospray ionization (ESI) hybrid techniques employ ns pulse durations. However, the amount of ablated myoglobin originating from a ns pulse was observed to be dependent on the amount of energy that was absorbed by the substrate or sample. Experiments to increase the signal intensity while implementing ns laser electrospray mass spectrometry (ns-LEMS) were performed by exploiting the optical properties of nanomaterials as a potential matrix for desorption and detection of myoglobin. To estimate the contribution of the surface plasmon resonance (SPR) to the desorption of myoglobin under the different pulse duration regimes, the addition of an aqueous gold nanostar (GNS) matrix was implemented. GNSs have a SPR maximum of ~750 nm which overlaps strongly with the 780 nm laser wavelength. Gold nanospheres, which have a SPR of ~530 nm, have an absorption overlap 25 times less than that of the nanostars with the 785 nm laser light and therefore were chosen as a control gold nanoparticle matrix. It was observed that protein mixed with solution phase GNSs improved the laser ablation and consequent mass spectral signal intensity of the protein in comparison to both the nanosphere addition and ablation from quartz without nanomaterial addition for the 55 fs, 56 ps, and 10 ns pulses. This dissertation also extends to an investigation of the electrospray source and the roles that the nebulizing gas pressure, electrospray solution flow rate, and needle protrusion from the emitter sheath effects the electrospray analyte signal and stability. Interactions between the electrospray droplets and nebulizing gas were elucidated using an ablation chamber in which laser ablated analytes were carried via the nebulizing gas flow through the nebulizer sheath to interact with the electrospray Taylor cone, jet, and subsequent droplets. The signal intensity and relative standard deviation (RSD) of an infused Victoria blue solution was used to assess conventional ESI optimization experiments while a mixture of Gly-Gly-His, lactose, adenosine, and vitamin B12 was laser ablated within the ablation chamber for the optimization of the remote ablation device. It was found that a needle protrusion flush with the nebulizing sheath wall, 9 psi nebulizing gas pressure, and 9 µL/min ESI flow rate yielded the highest signal intensity for low and high mass analytes when utilizing the ablation chamber. However, the conventional ESI signal and stability was maximized using a needle protrusion of 0.6 mm from the sheath, 18 psi nebulizing gas pressure, and 9 µL/ min ESI flow rate. The last two chapters describe collaborative efforts with GlaxoSmithKline (GSK) and Temple University’s Lewis Katz School of Medicine with the application of LEMS to real world problems. The first of these chapters explores the preliminary method development results for sampling protocols of LEMS in a pathway to measuring the active ingredient in a formulation when differences in concentration are a percent or less for GSK. The results from the method development and optimization experiments in the previous chapters were applied to the GSK pharmaceutical manufacturing paradigm to test product quality in-line and in real-time instead of testing in a lab at the end of the manufacturing process. The LEMS sampling protocols involved ablation of either powder, compressed form, or solution containing powder using laser ablation. The ablated material was then entrained in an electrospray aerosol and transferred into a mass spectrometer for quantitative measurement of the molecules making up the powder, pill, or solution. Measurement time was on the order of seconds so that thousands of samples can be potentially measured in an hour. Future prospective experiments include additional optimization of the solution phase and compressed form sampling methods and, ultimately, the method validation of LEMS for quantifying active ingredients in pharmaceutical formulations. The last chapter seeks to develop new methods to map all biomarkers in traumatic brain injury (TBI) through mass spectrometry imaging (MSI), serum analysis, and protein derivatization assays. In this work, the Ramirez laboratory employs the controlled cortical impact model of experimental TBI in mice, harvests the brain (post injury) and prepares sections for analytical analysis. TBI is a complex injury involving multiple physiological and biochemical alterations to tissue. The potentially thousands of relevant biomarkers spread over a volume of thousands of mm3 makes the spatially resolved chemical analysis of brain a big data problem to which principal component analysis is applied. / Chemistry

Diese Arbeit untersucht den Zusammenhang von elektronischer und nukleare Anregung beim Raman-Effekt mit der Methode der zeitaufgelösten harten UV-Spektroskopie. Wir verwenden kohärente stimulierte Raman-Streuung, ein Spezialfall der Standard-Raman-Streuung. Bei dieser regt ein hinreichend kurzer kohärenter Lichtimpuls Schwingungen der Kerne an, bei denen die Kerne messbar ausgelenkt werden, wohingegen die Auslenkungen bei normaler Raman-Streuung, wegen deren inkohärenten spontanen Natur, nicht messbar sind. Wir konnten Auslenkung kleiner als 10^-4 A in Echtzeit durch ihren Effekt auf das harte UV-Spektrum nachweisen. Diese Ergebnisse konnten mit Lithiumborhydrid als Probe und nicht-resonanter naher Infrarotstrahlung als Anrege-und harter UV-Strahlung als Abfrageimpuls erzielt werden. Zum Nachweis dieses Prozesses verwenden wir harte UV-Absorptionsspektroskopie an der Lithium K-Kante von Lithiumborhydrid bei 60 eV. Das Absorptionsspektrum besteht aus einem starken exzitonischen Anteil zu Beginn der Absorption und einem Plateau bei höheren Energien. Bei Anregung durch einen NIR-Impuls beobachteten wir eine oszillatorische Änderung des Absorptionsspektrums mit einer Frequenz von 10 THz, was wir der Modulation der interatomaren Abständen durch kohärente Phononen, und die damit einhergehende Modulation der chemischen Umgebung des absorbierenden Atoms, zuschreiben. Harte UV-Spektroskopie, insbesondere bei niedrigen Energien und nahe der Kante, ist hoch sensitiv auf die chemische Umgebung des jeweiligen absorbierenden Atoms. Unsere Resultate erlauben einen faszinierenden, neuen Einblick in die mikroskopische Natur des Raman-Effekts. Sie verbinden einen direkten Nachweis des antreibenden Mechanismus, der induzierten Polarisation, mit einer direkten Beobachtung des Resultats, die oszillatorische Auslenkung der Kerne. Dabei konnten mit harter UV-Spektroskopie nukleare Auslenkungen in der Größenordnung von 10-4 A mit Subpicosekundenzeitauflösung aufgelöst werden. / This thesis explores the subtle interplay between electronic and nuclear excitation in the Raman effect with time resolved XUV absorption spectroscopy. Coherent stimulated Raman scattering, the type of Raman interaction we induce, is a variant of the well known Raman scattering, where a sufficiently short pulse excites nuclear vibrations coherently, i.e. with actual displacement of the nuclei. In standard Raman scattering, due to its incoherent, spontaneous nature, there is no displacement of nuclei. We were able to observe nuclear displacements as small as 10^-4 in real time by their effect on the XUV absorption spectrum. Specifically we studied non-resonant NIR pump XUV probe absorption spectroscopy on lithium borohydride (LiBH_4). In the XUV absorption experiments in this thesis we concentrate on the Lithium K-edge absorption spectrum around 60 eV which consists of a strong excitonic peak at the onset of absorption and a plateau at higher energies. Upon excitation with a NIR pulse we observe oscillatory changes in the absorption spectrum with a frequency of 10 THz, which we identify as the effect of coherent phonon excitations of an external A_g phonon mode. The coherent oscillation changes the distance between Li^+ anions and BH_4^- cations, which modifies the electronic environment around the Li anion. XUV absorption spectroscopy, especially XANES, is highly sensitive to such changes of the chemical environment around the absorbing atom. We use two different approaches to derive the absolute displacement, which are observed in the experiment. Our results allow for a fascinating new insight into Raman scattering as they connect a direct observation of the driving mechanism, the induced polarization, with a direct observation of the outcome the oscillatory nuclear displacement. With XUV absorption spectroscopy nuclear displacements in the order of 10^-4 A were resolved with sub picosecond accuracy in the time domain.

Supercontinuum (SC) generation, oftentimes referred to as white-light continuum (WLC), has been a subject of interest for more than 40 years. From the first observation of WLC in condensed media in the early 1970s to the first observation of WLC in gases in the mid-1980s, much work has been devoted to developing a framework for understanding the complex nature of this phenomenon as well as discovering its utility in various applications. The main effort of this dissertation is to develop a WLC for the purpose of broadband nonlinear spectroscopy and use it in spectroscopic measurements. The ability to generate a high-quality, high-spectral-irradiance source of radiation confined in a single beam that spans the visible and near-infrared spectral regimes has great utility for nonlinear measurement methods such as the Z-scan technique. Using a broadband WLC instead of conventional tunable sources of radiation such as optical parametric generators/amplifiers has been shown to increase the efficiency of such measurements by nearly an order of magnitude. Although WLC generation has many complex processes involved, and complete models of the process involve highly complex numerical modeling, simple models can still guide us in the optimization of systems for WLC generation. In this dissertation the effects of two key mechanisms behind WLC generation in gaseous media are explored: self-phase modulation (SPM) and ionization leading to plasma production. The effects of SPM are largely dependent upon the third-order nonlinear refractive index, n2, of the gaseous medium whereas the effects of plasma production are dependent upon many parameters including the initial number density, ionization potential/energy, and the rate of ionization production. It is found that in order to generate a stable WLC suitable for nonlinear spectroscopy, the phase contributions from SPM and plasma production should be nearly equal. This guided our experiments in inert gases using mJ level, 150 fs-FWHM (full-width at half-maximum) pulses at 780 nm as well as 40 fs-FWHM pulses primarily at 1800 nm to create a stable, high-spectral-irradiance WLC. The generated WLC is shown to have sufficient spectral energy and spatial quality suitable for nonlinear spectroscopic measurements. In addition to extending the WLC bandwidth by using a long wavelength (1800 nm) pump source, it is found that by using a secondary weak seed pulse with a peak irradiance three orders of magnitude less than the main pulse, the spectral energy density is enhanced by more than a factor of 3 in Krypton gas for a WLC spectrum that spans over 2 octaves. Numerical simulations are presented which qualitatively describe the experimental results. The spectral enhancement of the WLC by seeding is also demonstrated for other inert gases and condensed media. Other efforts described in this dissertation include the development of the Dual-Arm Z-scan technique and its extension to measuring thin film nonlinearities in the presence of large substrate signals as well as predicting the n2 spectra of organic molecules (where we can approximate their behavior as if they were centrosymmetric) from knowledge of the one-photon and two-photon absorption spectra using a simplified sum-over-states quantum perturbative model by utilizing a quasi 3-level and quasi 4-level system.

Characterization of the dynamic behavior of defect-bearing ablator materials subjected to extreme conditions is essential in advancing fusion energy as an reliable and abundant energy source. By understanding how materials evolve spatially and temporally we can minimize hydrodynamic instabilities, which are major contributing factors to energy yield degradation in inertial confinement fusion (ICF) experiments. In this thesis we demonstrate the capabilities of an ultrafast x-ray imaging (UXI) detector, the Icarus V2, where we capture multiple frames of single void-bearing sample compressed by a high-intensity laser shockwave. Using the Matter in Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS), we conducted two experiments with the x-ray free electron laser (XFEL) multi-pulse mode, delivering four nanosecond-separated pulses to a sample impacted by a laser shockwave, obtaining multiframe images of a single sample in the holographic and direct imaging regime with the UXI detector. In contrast to the low temporal resolution provided by current cameras, the Icarus V2 can capture images with high temporal resolution, which can be used to determine the mechanisms that prevent thermonuclear ignition in ICF experiments. For images captured in the holographic regime at our XFEL energy of 8.23 keV, we realized that the shock front was obscured by strong phase-contrast effects. We recognized that by increasing the XFEL energy while in the holographic regime, more distinguishable features could be revealed behind and along the shock front. Alternatively, in the direct-imaging configuration we discovered that the evolution of microstructural features were directly recognizable in comparison to the holographic regime at lower XFEL energies. Overall, the images captured by the UXI in both regimes demonstrated our ability to obtain multiframe images of processes that occur over several nanoseconds for single samples, which has never been done before. Moreover, the capabilities of the UXI enable extraction of quantitative information over multiple frames, which can help with uncovering the underlying physics involved in high energy density (HED) physics experiments and other experiments involving non-repeatable ultrafast phenomena. Specifically, insight into the behavior of the void can be gained by performing phase retrieval on the images and obtaining the areal density of the materials during laser-shock ablation. Generally, the UXI improves data acquisition speed and operational efficiency, which extends this camera's functionality to experiments that occur at various time scales or experiments that require multiple images to be captured.

<p> </p> <p>High-speed flows are important for defense, national security, and transportation applications and generate harsh environments where simplifying assumptions such as the ideal gas law are not valid due to nonequilibrium and chemistry effects. These flows are difficult and expensive to replicate experimentally, so the development and improvement of high-speed vehicles often relies on high-fidelity computational fluid dynamics (CFD) models. The successful modeling of complicated phenomena, such as heat transfer in a turbulent boundary layer, relies on validation by experimental data taken with high spatiotemporal resolution, precision, and accuracy. Precise experimental measurement of temperature, an important thermodynamic property for CFD models, is difficult with physical probes which are typically slow and perturb the flow. Instead, hybrid femtosecond/picosecond (fs/ps) coherent anti-Stokes Raman scattering (CARS) allows for non-intrusive, spatially-resolved, collision-free thermometry at kHz repetition rates with high precision and accuracy. </p> <p>The goal of this thesis is to advance hybrid fs/ps CARS for extension to high-speed flows, with particular improvements to the spatial extent, probe characteristics, and precision of the technique. A novel method for multipoint measurements in a simple and effective optical arrangement is demonstrated, enabling single-shot and averaged measurements of temperature and O₂/N₂ concentration along a linear array of probe volumes. The generation of a variable-pulsewidth probe beam by a ps slicer, electro-optic modulator, fiber amplifier, and custom narrowband amplifier system is used for improved signal-to-noise ratios at low pressure. Simultaneous CARS thermometry and femtosecond laser electronic excitation tagging (FLEET) velocimetry are performed in the freestream of Mach 3 and Mach 4 nitrogen flows. These measurements reveal the need to quantify and establish the ultimate precision of the hybrid fs/ps CARS technique. Sources of uncertainty in hybrid fs/ps CARS thermometry are determined through a theoretical uncertainty analysis and the predicted precision of the technique is confirmed experimentally in room temperature nitrogen. Benchtop measurements in a supersonic nozzle are used to indicate spatial and temporal simultaneity between FLEET and CARS measurements and hybrid fs/ps CARS thermometry is performed in a high-speed, low temperature flow.</p>

Die optischen Eigenschaften von Übergangsmetall-Dichalcogeniden (TMDC) werden durch Exzitonen (exc) dominiert, was auf den Quanteneinschluss und die reduzierte Abschirmung zurückzuführen ist, die für ihre 2D-Natur charakteristisch sind. Das Coulomb-Screening spielt eine grundlegende Rolle bei der Bestimmung der stationären und dynamischen Eigenschaften solcher Materialien. Zeitaufgelöste optische Spektroskopie ist ein grundlegendes Instrument, um die Rolle der Abschirmung in der Nicht-Gleichgewichtsphysik von TMDC zu untersuchen. Ich untersuche WS2-Monoschichten auf verschiedenen Substraten mit zeitaufgelöstem Transmissions-/Reflexionskontrast. Ich stelle einen Formalismus vor, der einen zuverlässigen Vergleich der dynamischen Reaktion der Exzitonen unabhängig von Probe, Substrat und Messtechnik ermöglicht. Mit diesem Formalismus werden die von der Pump-Photonen-Energie und der Fluenz abhängige Verschiebung und Verbreiterung des Exziton-Peaks extrahiert und mit Hilfe eines Zwei-/Drei-Niveau-Modells reproduziert. Mit Hilfe dieses Modells konnte die Konkurrenz zwischen dynamischer Abschirmung der Quasiteilchen, Streuung und thermischen Effekten entschlüsselt werden. Die Verbreiterung wird durch QFC-exc (exc-exc) Streuung bestimmt, wenn QFC (exc) im System vorhanden sind. Darüber hinaus induzieren QFC (exc) eine globale Rot-(Blau-)Verschiebung der Exzitonenresonanz, die mit einer effektiven QFC (exc) dynamischen, abschirmungsinduzierten Renormalisierung der Bandlücke (Verringerung der Bindungsenergie) reproduziert wird. Schließlich wird der Einfluss der statischen Abschirmung auf die Reaktion der Exzitonen untersucht. Die dynamische exc-Abschirmung ist bei höherer Substratpermittivität verstärkt und wird versuchsweise auf einen höheren Grad der Delokalisierung des Exzitons zurückgeführt. Letztlich trägt diese Arbeit zu einem umfassenden Bild der Nicht-Gleichgewichtsdynamik und der Rolle der Abschirmung in TMDC bei. / The optical properties of transition metal dichalcogenides (TMDC) are dominated by excitons, due to quantum confinement and reduced screening characteristic of their 2D nature. Exactly the screening of the Coulomb interaction has a fundamental role in determining the steady-state and dynamic properties of such materials. Time-resolved optical spectroscopies are a fundamental tool to investigate the phenomena governing the non-equilibrium physics of TMDC materials. Nevertheless, the quantitative role of the screening in the non-equilibrium response of the TMDC is yet to be understood. I investigate monolayers WS2 placed on various substrates with time-resolved transmittance/reflectance contrast. I report a formalism that allows the reliable comparison of the exciton dynamic response independently of sample, substrate and measurement technique. With this formalism, the pump-photon energy and fluence-dependent exciton peak shift and broadening are extracted and reproduced using a basic two/three-level model. Through this model the competition of quasiparticle dynamic screening, scattering and thermal effects was unravelled. The broadening is governed by QFC-exciton (exciton-exciton) scattering when QFC (excitons) are present in the system. Furthermore, QFC (excitons) induce a global red-(blue-)shift of the exciton resonance, reproduced with an effective QFC (excitons) dynamic screening-induced bandgap renormalization (binding energy reduction). Finally, the static screening influence on the non-equilibrium exciton response is addressed. Scattering and QFC dynamic screening are unaffected in different dielectric environments. On the contrary, the exciton dynamic screening is enhanced for higher substrate permittivity and possibly due to a higher degree of delocalization of the exciton. Ultimately, this thesis contributes to a comprehensive picture of the non-equilibrium dynamics and the role of screening in TMDC.

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