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This dissertation details the design and implementation of a state-of-the-art ambient trace analysis technique known as laser electrospray mass spectrometry. This novel technique utilizes an intense, nonresonant femtosecond laser pulse to transfer nonvolatile, fragile molecules into the gas phase from various substrates. The vaporized analyte is subsequently captured, solvated and ionized in an electrospray plume enabling mass analysis. Laser electrospray mass spectrometry is capable of analyzing samples in the liquid or solid states, mass spectral imaging of adsorbed molecules and detecting low vapor pressure analytes remotely. Experiments with biomolecules and pharmaceuticals, such as vitamin B12 and oxycodone, have demonstrated that the nonresonant femtosecond laser pulse allows for coupling into and vaporization of all molecules. This implies that sample preparation (elution, mixing with matrix and choosing samples with a particular electronic or vibrational transition) is not necessary, thus creating a universal mass analysis technique. Investigations using low vapor pressure molecules, such as lipids and proteins, led to the discovery that unfragmented molecules are transferred into the gas phase via a nonthermal mechanism. The laser electrospray mass spectrometry technique has allowed for the nonresonant femtosecond laser vaporization and mass analysis of trace amounts of a nitro-based explosive from a metal surface. The vaporization of unfragmented explosive molecules from a surface facilitates the identification of the explosive, reducing the probability of false positives and false negatives. In addition, this "soft" vaporization of molecules using nonresonant femtosecond laser pulses allows for protein to be transferred from the condensed phase into the gas phase without altering the molecule's structure, enabling ex vivo conformational analysis and possible disease typing. / Chemistry

The use of femtosecond (fs) laser pulses in laser-induced breakdown spectroscopy (LIBS) and for chemical analysis using mass spectrometry is explored. A comparison of fs-LIBS and remote filament-induced breakdown spectroscopy (R-FIBS) in the analysis of graphite composites yielded more accurate results with filaments due to intensity clamping within the filament. The investigation of fs-LIBS and R-FIBS in the detection of explosives led to the discovery of femtosecond vaporization of intact molecules under ambient conditions. This knowledge was then used in the development of a new ambient laser-based mass analysis technique. The combination of nonresonant femtosecond laser vaporization with electrospray post-ionization called laser electrospray mass spectrometry (LEMS) was investigated as a universal detection method of pharmaceuticals, biological macromolecules and plant tissues. We show the capability of femtosecond lasers to desorb sample without any sample preparation or resonant transition in the sample or substrate. Ambient mass spectral imaging and tissue type classification is also demonstrated. / Chemistry

Adipose tissue is a type of connective tissue whose purpose was once thought to be limited to fat storage but is now understood to be a key factor in the pathogenesis of different metabolic diseases, including obesity and type-II diabetes. Adipose tissue consists largely of adipocytes, cells responsible for fat and releasing energy in form of lipids. Different classes of fatty acids, such as saturated and unsaturated have different biological effects on adipocytes. Lipid droplets are the primary organelles in adipocytes that store these fatty acids in form of lipids, and the development of engineered adipose tissues would benefit from improved techniques for analysis of lipid droplet composition, distributions, and dynamics based as a function of fatty acid saturation. Conventional microscopic techniques, such as fluorescence microscopy, provides excellent selectivity of lipid-based structures inside adipose tissue cellular structures based on staining with compound dyes. However, fluorescence staining limits multiplex imaging, and requires time consuming steps in preparing the samples for imaging. Therefore, developing a label-free, high resolution imaging platform with sensitivity to lipid composition could enable analysis of structural and compositional differentiation of lipid droplets within adipocytes during differentiation could give valuable insights into the importance of lipid droplets role in metabolism. As an important step towards achieving this goal, a femtosecond based CARS microscopy imaging platform has been developed to perform in vitro, label-free, imaging of fatty acid composition within engineered adipose tissues. / Bioengineering

No doubt, water is the most important liquid on the planet. In addition to the obligatory need for water in life, water is widely used in diverse applications. In most applications if not all, water is interfaced with different materials, at different phases depending on the application. This unique value of water originates from its chemical structure, which is based on hydrogen bonding. Although these chemical bonding in bulk liquid and vapor water have extensively been investigated, in interfacial water are not yet fully understood. This thesis presents an investigation of ultrafast vibrational dynamics of hydrogen bonding in interfacial water. In a first chapter, the experimental technique and tools needed for the study of interfacial vibrational dynamics are exposed. In the first part of a second chapter, vibrational coherence dynamics of free OH stretch modes at the alumina/water interface are investigated. And in the second part, vibrational coherence dynamics of hydrogen bonded OH stretch modes at the calcium fluoride/water interface are investigated. To understand the dynamics of vibrational energy flow within an interfacial network of hydrogen bonding, the investigation of vibrational coupling dynamics at the calcium fluoride/water interface takes place in a third chapter. Unlike what has already been reported in this topic, in our work, the vibrational energy will be initially deposited at the second vibrational excited state, through an overtone transition. / Chemistry

This dissertation expounds growing insight of the electrospray droplet ionization mechanism following ablation of dried hydrophobic and hydrophilic molecules using femtosecond laser pulses and mass analysis of the gas phase ions. Both hydrophobic and hydrophilic molecules were laser vaporized into an electrospray solvent opposite in polarity revealing appreciable ion intensity for all samples in contrast to ESI-MS and DESI measurements were solubility of the analyte in the spray solvent is a prerequisite. Quantitative analysis of equimolar protein solutions was established using LEMS reporting over three decades of quantitave response with little evidence of ion suppression. In contrast, ESI-MS measurements of similar equimolar protein solutions revealed severe ion suppression eliminating ion current from one of the protein analytes. Finally, the nature of an analyte following nonresonant laser vaporization has been the subject of debate. Aqueous trypsin was laser vaporized into an electrospray solvent containing either buffer or acid with substrate. LEMS measurements using buffer revealed enzyme-substrate intermediate charge states and continued enzymatic activity while the lack of enzyme-substrate intermediates and stymied enzymatic activity observed using acid suggests nonresonant laser vaporization preserves solution phase structure. This dissertation also extends considerably the use of LEMS for identification and characterization of energetic materials in their pre- and post-blast forms without sample preparation. The use of mulivarate analysis for the classification of large sample sets was also demonstrated showing high fidelity assignment of commercial formulations to their manufacturer. Five unburnt smokeless powders investigated using LEMS revealed unique combinations of organic molecules such as stabilizers and plasticizers using a simple electrospray solvent. Principal component analysis (PCA) provided exact classification of the mass spectra with respect to the manufacturer of the ordinance. LEMS measurements were then obtained from five commercial gunshot residue samples, or post-blast smokeless powder, revealing trace amounts of organics such as the stabilizers and large quantities of inorganic barium originating from the primer. Principal component analysis (PCA) again provided exact classification of the gunshot residue mass spectra with respect to the manufacturer of the ordinance. The use of a common transition metal complexation agent enabled full characterization of eight gunshot residue samples to include the heavy metals contained in the primer and the organics such as the stabilizers and plasticizers without any sample preparation or pre-concentration procedures. Principal component analysis (PCA) again provided high fidelity classification of the gunshot residue mass spectra with respect to the manufacturer of the ordinance after mass analysis with LEMS. Finally, highly energetic formulations such as composition 4 (C-4) and detonation cord subjected to nonresonant femtosecond laser vaporization enabled full characterization of these complex compositions identifying binders, stabilizers, the explosive ingredient and age-related decomposition derivative signature molecules with appreciable ion current detected using both positive and negative ion modes. / Chemistry

<p> Lithium niobate is an important photonic material that has potential applications in MEMS. Unfortunately, it is difficult to process using conventional methods. This thesis is an exploratory study to determine the viability of using a femtosecond laser as a fabrication tool for lithium niobate. Unexpectedly, a rich range of behaviour, likely arising from the complex material structure and composition, was discovered. Depending on the processing conditions, it was demonstrated that machining can either result in deep, high-aspect ratio grooves with minimal surrounding damage or dramatic modification of the lithium niobate to great depths with very little material removal.</p> <p> When machining grooves, increasing the effective number of pulses Neff (i.e. decreasing cutting speed) gave rapidly increasing ablation depths until a threshold was reached, after which the grooves were nearly filled with amorphous material. The depth of these amorphous channels rapidly saturates and becomes nearly independent of Neff. The ablation depth dependence on fluence showed gentle and strong ablation regimes. The amorphous channel depth depended almost linearly on fluence. Subsequent laser passes over amorphous channels eventually removed the amorphous material from the groove, indicating a dependence on the time between laser pulses. Crystal orientation was not a factor.</p> <p> The results are understood in terms of incubation and wave guiding. The first pulses ablate some material and incubate a channel of material below the surface. With further pulses, increasing incubation accelerates ablation. At the threshold Neff, the absorption coefficient has increased enough that the next pulse is able to melt a significant amount of material, which expands to fill the groove. It is suggested that, initially, the amorphous material is able to guide subsequent pulses to the bottom of the channel, resulting in a very slowly increasing depth with Neff. Subsequent passes cause ablation once again since compositional changes in the amorphous material have relaxed. Irradiated samples appear thermally reduced, which would create colour centres leading to increased absorption and thus incubation.</p> <p> Femtosecond lasers are indeed able to create MEMS structures. Multiple passes in the ablation regime yielded deep grooves, with laser polarization perpendicular to the groove giving the best results. Fabrication of micro-cantilevers and bridges was demonstrated.<p> / Thesis / Master of Applied Science (MASc)

This thesis reports on the development of glass-based femtosecond laser sources around 2 µm wavelength. In order to be able to produce 2 µm radiation the dopants used were trivalent Thulium (Tm³⁺) and trivalent Holmium (Ho³⁺) that could be optically pumped with Ti:Sapphire radiation at 0.8 µm and semiconductor disk lasers (SDL) at 1.2 µm. The samples were produced at Leeds University and polished in-house in bulk form and deployed in free space laser cavities. Tellurite compounds doped with Tm³⁺ produced stable continuous wave 1.94 µm radiation when pumped at 800 nm with a maximum efficiency of 28.4% with respect to the absorbed power and maximum output power around 120 mW when pumped using a Ti:Sapphire operating around 0.8 µm. The radiation was broadly tunable across 130 nm. Tm³⁺-Ho³⁺ doubly doped tellurite samples lased around 2.02 µm with maximum efficiency of 25.9% and with P[subscript(OUT)]=75 mW and a smooth tunability of 125 nm. The fluorogermanate glass doped with Tm³⁺ gave an absorbed to output power efficiency of 50%. The maximum continuous wave output powers obtained were around 190 mW and limited by the available pump power at 0.8 µm. These results together with a very low threshold of 60 mW of incident power were comparable to the crystalline counterparts to this gain medium. The Tm3+ tellurite and the Tm³⁺-Ho³⁺ tellurite compounds were also pumped by an SDL operating at 1215 nm to obtain an indication of the viability of such a pump scheme. The results were a maximum internal slope efficiency of 22.4% with a highest output power of 60 mW. The comparison demonstrated that 1.2 µm pumping was competitive with using 0.8 µm wavelength. The use of semiconductor saturable absorbing mirror (SESAM) technology was used for the modelocking of these lasers. The SESAM was produced in Canada and implanted with As⁺ ions in order to reduce the relaxation time. Trains of transform-limited laser pulses at 222 MHz as short as 410 fs centred at 1.99 µm were produced for the first time with a bulk Tm³⁺:Fluorogermanate glass. The maximum average output power obtained was of 84 mW. The same SESAM deployed on the Tm³⁺-Ho³⁺ Tellurite compounds gave trains of transform-limited pulses as short as 630 fs at 2.01 µm with a repetition rate of 143 MHz and a maximum averaged output power of 43 mW. The regime of propagation obtained was soliton-like and the modelocking was self-starting. The results obtained with bulk glass were very promising and open interesting research pathways within the realm of amorphous bulk gain media.