In Chapter 1, we present the background for transient absorption spectroscopy through the polarization response of a material to an electric field which gives rise to linear and non-linear processes. We then discuss a theoretical description of how vibrational coherences are formed via four-wave mixing and impulsive excitation. We also describe signatures of coherent wavepackets in transient absorption and the application of vibrational coherences, specifically to observe non-radiative processes. We then summarize two previous studies using impulsive transient absorption on cresyl violet, the differences in the coherent dynamics reported, and the motivations behind the experiments presented in this work. Chapter 2 pertains to the apparatus used to perform the transient absorption experiments. We detail the source for the generation of ultrashort laser pulses (durations of less than 10 fs) used for the pump and probe from an argon-based white-light filament and non-colinear optical parametric amplifier. Two-dimensional shearing interferometry, the method used to measure the ultrashort pulses across a large portion of the visible spectrum (500-750 nm), is discussed. The retrieved temporal, spectral, and phase profiles of the pump and probe pulses are presented. Finally, the sample preparation for cresyl violet is described as well as the detection method and data processing used to generate the figures throughout this work. In Chapter 3, we present the results of impulsive transient absorption spectroscopy of cresyl violet perchlorate under four pump conditions. First, we report a study on controlling the formation of vibrational coherences on the ground or excited electronic states of cresyl violet by tuning the pump conditions from an off-resonant to a resonant scheme. The decay of the electronic population and positions of the stimulated emission and excited-state absorption maximums shows a dependence on the pump wavelength. Higher excitation frequencies blueshifts the stimulated emission 18 meV and red shifts excited-state absorption by 4 meV at early times compared to only 13 meV and 2 meV when using lower excitation frequencies. Coherent vibrations are observed and persist for approximately 6 ps after excitation, with phase flips appearing at 593 nm, the absorption maximum, after off-resonant excitation and at the emission (619 nm) and excited-state absorption (500 nm) maximums after resonant excitation. The ground- and excited-state vibrational modes are characterized by Fourier transform Raman spectroscopy. The excited-state vibration spectrum is shown to share nearly identical features as the ground-state, with each vibration slightly red-shifted, 2-10 cm-1, from the corresponding mode in the ground-state, particularly a prominent peak appearing at 594 cm-1 in the ground-state and 589 cm-1 in the excited-state. Next, two additional pump conditions using broadband and partially resonant pump pulses are explored to replicate the conflicting reports of non-adiabatic crossings in cresyl violet. Constant phase-flips observed in the control studies are replaced with phase flips that appear and disappear over several picoseconds. The Fourier Raman spectrum of the coherent signal after broadband excitation displays a mix of ground- and excited-state features, particularly prominent peaks at both 589 cm-1 and 594 cm-1. In Chapter 4, we analyze the coherent signals after broadband excitation using a Fourier filtering technique to isolate the ground- or excited-state coherent dynamics by carefully selecting representative vibrational modes for each state. Using a narrow filter to isolate the 589 cm-1 and 595 cm-1 features in the broadband Fourier Raman spectrum successfully isolates coherent vibrations with phase flips at either the emission and excited-state absorption maximums or the ground-state absorption maximum, respectively. A filter that includes both features generates apparent phase-flips that only appear for ~1ps and at probe wavelengths that do not correspond to the emission or absorption maximums. In Chapter 5, we present a simulation of the coherent signals using a model of two wavepackets with carrier frequencies of 589 cm-1 and 595 cm-1 and dephasing rates of 2 and 3 ps, respectively. Comparison to the broadband pump conditions and Fourier filtered coherent oscillations shows that the complex temporal dynamics observed are adequately described by the linear interference of two vibrational coherences evolving on different electronic potential energy surfaces, without the need to invoke non-adiabatic dynamics. / Chemistry

Mild traumatic brain injury (mTBI), often referred to as concussion, has become increasingly recognized as a serious health issue in the general population. The prevalence of mTBI in athletes, particularly repeated injuries in young athletes, is of great concern as injuries to the developing brain can have long-term detrimental effects. In this study we used a novel awake closed-head injury (ACHI) model in rodents to examine repeated mTBI (rmTBI), to determine if repeated injuries produced the neurological and molecular changes evident with human concussion. Animals were administered 4, 8, and 16 rmTBIs and acute neurological assessments were performed after the injuries. Changes in glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba-1) levels were assessed using Western blot analysis at one day following rmTBI in the ipsilateral dentate gyrus (DG) and the cornu ammonis (CA) regions of the hippocampus and the cortex (CX) indicative of astrocyte and microglial cell reactivity. Results indicated that the ACHI model produces neurological deficits immediately after the injuries, with the most deficits arising in the rmTBI16 group. Despite deficits in all injury groups, histological staining with cresyl violet revealed no significant morphological tissue damage to the brain. Western blot analysis, however, showed a significant increase in DG and CX GFAP expression in the rmTBI16 group with no changes in Iba-1 levels. This suggests an acute activation of astrocytes in response to injury, with a delay or absence of microglial activation. Our findings show that with repetitive concussions, we are able to detect acute neurological and molecular changes in the juvenile female brain. However, further investigation is necessary to determine if these are transient changes. / Graduate

Hjärnan innehåller bland annat neuroner och glia celler. Soma där nukleus samt nissl substans påträffas samt axon som isoleras av myelin anträffas i en neuron. Genom färgningen Luxol Fast Blue (LFB) med kresylviolett färgas myelinet blått av LFB och cellkärnor samt nissl substans rosa-violett av kresylviolett. Syftet med studien var att optimera Luxol Fast Blue med kresylviolett infärgningsmetoden på hjärnvävnad med avseende på koncentration, mängd tillsatt 10 % ättiksyra och därmed pH, färgning i värme samt undersöka kresylviolett-lösningens hållbarhet. Från färgningen graderades LFB intensiteten, kresylviolett intensiteten samt bakgrunds infärgning av kresylviolett från 0-3 där 0 ansågs en negativ infärgning, 1 en svag infärgning, 2 en måttlig infärgning och 3 en stark infärgning. Infärgningen optimerades genom en ökning av kresylviolett koncentrationen där koncentrationen 0,05 % ansågs optimalt. En tillsatt mängd av 10 % ättiksyra tills pH:et når 3,3-3,4 konkluderades även vara optimalt. 0,05 % kresylviolett-lösningen visades även kunna återanvändas i åtminstone 5 veckor, men troligtvis längre, och färgningen med kresylviolett-lösningen bör ske i rumstemperatur. / The brain contains, among other things, neurons and glial cells. Soma where nucleus and nissl substance are found and axon isolated by myelin is found in a neuron. Through the staining Luxol Fast Blue (LFB) with cresyl violet, the myelin is colored blue by LFB and cell nuclei as well as nissl substance pink-violet by cresyl violet. The purpose of the study was to optimize Luxol Fast Blue with the cresyl violet staining method on brain tissue with respect to concentration, amount of added 10 % acetic acid and thus pH, dyeing in heat and to investigate the durability of the cresyl violet solution. From the staining, the LFB intensity, the cresyl violet intensity and the background staining of cresyl violet were graded from 0-3 where 0 was considered a negative staining, 1 a weak staining, 2 a moderate staining and 3 a strong staining. The staining was optimized by an increase in the cresyl violet concentration where the concentration of 0,05 % was considered optimal. An added amount of 10 % acetic acid until the pH reaches 3,3-3,4 was also concluded to be optimal. The 0,05 % cresyl violet solution was also shown to be reusable for at least 5 weeks, but probably longer, and the staining with the cresyl violet solution should take place at room temperature.