This work focuses on finding the complete iodine and nitrogen nuclear electric quadrupole coupling tensors for fluoroiodoacetonitrile using chirped-pulse Fourier transform microwave spectroscopy. Fluoroiodoacetonitrile contains two hyperfine nuclei, iodine (I=5/2) and nitrogen (I=1) and the spectra were observed with great resolution. A total of 499 transitions were observed for this molecule. The a, b and c rotational constants were obtained. A study of chloropentafluoroacetone was also done using chirped-pulse Fourier transform microwave spectroscopy. The two chlorine isotopes for this molecule, Cl-35 and Cl-37 were observed and 326 and 170 transitions were recorded, respectively.

Distributed optical fiber sensors offer unprecedented advantages, and the most remarkable one is the ability to continuously measure physical or chemical parameters along the entire optical fiber, which is attached to the device, structure and system. As the most recently investigated distributed optical fiber sensors, phase-sensitive optical time domain reflectometry (φ-OTDR), Brillouin optical time domain analysis (BOTDA) and Brillouin dynamic grating-optical time domain reflectometry (BDG-OTDR) techniques have been given tremendous attention on the advantage of quantitative measurements ability over high sensitivity and absolute measurement with long sensing distance, respectively. However, the accompanying limitations in terms of static measurement range, acquisition rate, laser frequency drifting noise, and spatial resolution limitations in these techniques hinder their performance in practical applications. This thesis pays particular attention to the above three distributed sensing techniques to explore the fundamental limitations of the theoretical model and improve the sensing performance. Before presenting the novel sensing scheme with improved sensing performance, an introduction about distributed fiber optical sensing, including three main light scattering mechanisms in optical fiber, the recent advancements in distributed sensing and key parameters of Rayleigh scattering- and Brillouin scattering-based sensing systems. After that, a study on the theoretical analysis of large chirping rate pulse generation and the theoretical model of using chirped pulse as interrogation signal in φ-OTDR, BOTDA and BDG-OTDR systems are given. In the disruptive experimental implementations, the sensing performance has been improved in different aspects. By using a random fiber grating array as the distributed sensor, a high-precision distributed time delay measurement in a CP φ-OTDR system is proposed thanks to the enhanced in-homogeneity and reflectivity. In addition, a simple and effective method that utilizes the reference random fiber grating to monitor the laser frequency drifting noise is demonstrated. Dynamic strain measurement with a standard deviation of 66 nε over the vibration amplitude of 30 με is achieved. To solve the limited static measurement range issue, a multi-frequency database demodulation (MFDD) method is proposed to release the large strain variation induced time domain trace distortion by tuning the laser initial frequency. The maximum measurable strain variation of about 12.5 με represents a factor of 3 improvements. By using the optimized chirped pulse φ-OTDR system, a practical application of monitoring the impact load response in an I-steel beam is demonstrated, in which the static and distributed strain variation is successfully reconstructed. To obtain an enhanced static measurement range without a complicated database acquisition process, a photonic approach for generating low-frequency drifting noise, arbitrary and large frequency chirping rate (FCR) optical pulses based on the Kerr effect in the nonlinear optical fiber is theoretically analyzed and experimentally demonstrated by using both fixed-frequency pump and chirped pump. Due to the Kerr effect-induced sinusoidal phase modulation in the nonlinear fiber, high order Kerr pulse with a large chirping rate is generated. Thus the static measurement range of higher order Kerr pulse is significantly improved. Chirped pulse BOTDA based on non-uniform fiber is also analyzed, showing a high acquisition rate that is only limited by the sensor length and averaging times due to the relative Brillouin frequency shift (BFS) changes are directly extracted through the local time delays between adjacent Brillouin traces from two single-shot measurement without frequency sweep process. BFS measurement resolution of 0.42 MHz with 4.5 m spatial resolution is demonstrated over a 5 km non-uniform fiber. A hybrid simultaneous temperature/strain sensing system is also demonstrated, showing a strain uncertainty of 4.3 με and temperature uncertainty of 0.32 °C in a 5 km non-uniform fiber. Besides, the chirped pulse is also utilized as a probe signal in the Brillouin dynamic grating (BDG) detection along the PM fiber for distributed birefringence variations sensing. The strict phase-matching condition only enables part of the frequency components within the chirped probe pulse to be reflected by BDG, giving an adjustable spatial resolution without photo lifetime limitation. The spatial resolution is determined by the frequency chirping rate of the probe pulse.

Microwave spectroscopy is a gas phase technique typically geared toward measuring the rotational transitions of Molecules. The information contained in this type of spectroscopy pertains to a molecules structure, both geometric and electronic, which give insight into a molecule's chemistry. Typically this type of spectroscopy is high resolution, but narrowband ≤1 MHz in frequency. This is achieved by tuning a cavity, exciting a molecule with electromagnetic radiation in the microwave region, turning the electromagnetic radiation o, and measuring a signal from the molecular relaxation in the form of a free induction decay (FID). The FID is then Fourier transformed to give a frequency of the transition. "Fast passage" is defined as a sweeping of frequencies through a transition at a time much shorter (≤10 s) than the molecular relaxation (≈100 s). Recent advancements in technology have allowed for the creation of these fast frequency sweeps, known as "chirps", which allow for broadband capabilities. This work presents the design, construction, and implementation of one such novel, high-resolution microwave spectrometer with broadband capabilities. The manuscript also provides the theory, technique, and motivations behind building of such an instrument. In this manuscript it is demonstrated that, although a gas phase technique, solids, liquids, and transient species may be studied with the spectrometer with high sensitivity, making it a viable option for many molecules wanting to be rotationally studied. The spectrometer has a relative correct intensity feature that, when coupled with theory, may ease the difficulty in transition assignment and facilitate dynamic chemical studies of the experiment. Molecules studied on this spectrometer have, in turn, been analyzed and assigned using common rotational spectroscopic analysis. Detailed theory on the analysis of these molecules has been provided. Structural parameters such as rotational constants and centrifugal distortion constants have been determined and reported for most molecules in the document. Where possible, comparisons have been made amongst groups of similar molecules to try and get insight into the nature of the bonds those molecules are forming. This has been achieved the the comparisons of nuclear electric quadrupole and nuclear magnetic coupling constants, and the results therein have been determined and reported.

The goal of this thesis is developing a two-color Ytterbium (Yb) fiber amplifier system that can be used for generation of mid-infrared radiation. Previously, our group reported generating 20 µW of average power, at a wavelength of 18µm. This was accomplished through the amplification of a two color-seed with peaks at 1040nm and 1110nm, through a two stage amplification without any compression. The mid-infrared radiation (MIR) was generated with a 4.5 ps pulse duration by the method of difference-frequency mixing, using 300 mW of average power from the two-color Yb-fiber amplifier. Because there was no limitation by two-photon absorption, MIR output power could be scaled by increasing the amplifier power. The current project aims to increase the peak power of the laser pulses to improve the efficiency of the nonlinear mixing. The two-colour seed is generated by continuum generation in a photonic crystal fibre, pumped by 200 mW of average power from a mode-locked Yb:fibre laser. In order to efficiently increase the energy of the two wavelengths, the 4.6 mW seed pulse is now pre-amplified up to 21 mW in a 2.7 m length single mode, single core Yb:fibre . The pre-amplifier used a double-ended pumping scheme with two single mode diode lasers at 976 nm each having 150 mW maximum pump power. A notch filter was placed in the output beam to eliminate any Amplified Spontaneous Emission. After further amplification in a 7 m length of double clad, Yb-fibre, a maximum average power of 727 mW was achieved for two colours peaked at 1035 nm and 1105 nm wavelengths. The pump power for this stage was 6 W. A grating stretcher is now used to select the two-colour input along with stretching the pulses. A three grating compressor is used to compress the output pulses to 466 fs pulse duration. After compression the average power of the two colours is 350 and 110 mW for wavelengths at 1035 and 1105nm, respectively. These higher power pulses are planned to be used to increase the mid-infrared generation efficiency.

The goal of this thesis is developing a two-color Ytterbium (Yb) fiber amplifier system that can be used for generation of mid-infrared radiation. Previously, our group reported generating 20 µW of average power, at a wavelength of 18µm. This was accomplished through the amplification of a two color-seed with peaks at 1040nm and 1110nm, through a two stage amplification without any compression. The mid-infrared radiation (MIR) was generated with a 4.5 ps pulse duration by the method of difference-frequency mixing, using 300 mW of average power from the two-color Yb-fiber amplifier. Because there was no limitation by two-photon absorption, MIR output power could be scaled by increasing the amplifier power. The current project aims to increase the peak power of the laser pulses to improve the efficiency of the nonlinear mixing. The two-colour seed is generated by continuum generation in a photonic crystal fibre, pumped by 200 mW of average power from a mode-locked Yb:fibre laser. In order to efficiently increase the energy of the two wavelengths, the 4.6 mW seed pulse is now pre-amplified up to 21 mW in a 2.7 m length single mode, single core Yb:fibre . The pre-amplifier used a double-ended pumping scheme with two single mode diode lasers at 976 nm each having 150 mW maximum pump power. A notch filter was placed in the output beam to eliminate any Amplified Spontaneous Emission. After further amplification in a 7 m length of double clad, Yb-fibre, a maximum average power of 727 mW was achieved for two colours peaked at 1035 nm and 1105 nm wavelengths. The pump power for this stage was 6 W. A grating stretcher is now used to select the two-colour input along with stretching the pulses. A three grating compressor is used to compress the output pulses to 466 fs pulse duration. After compression the average power of the two colours is 350 and 110 mW for wavelengths at 1035 and 1105nm, respectively. These higher power pulses are planned to be used to increase the mid-infrared generation efficiency.

Biomedical imaging requires high resolution to see the fine features of a sample and fast acquisition to observe live cells that move. Optical coherence tomography (OCT) is a powerful technique which uses optical interference for non-invasive high resolution 3D imaging in biological samples. The resolution of OCT is determined by the length over which the light used will in- terfere. Unfortunately, dispersion hurts the imaging resolution by broadening interference features. A technique called quantum-OCT (QOCT)[1] is immune to dispersion but re- quires entangled photon pairs. The need for entanglement drastically reduces the number of photons available for imaging, making QOCT too slow to be practical. Chirped-pulse interferometry (CPI) is also immune to dispersion. A chirped pulse is one where the fre- quency, or colour, of the light changes from red to blue from one end of the pulse to the other. CPI relies on frequency correlations created by applying different chirps to two sep- arate pulses. This method had the disadvantage of being limited to a single predetermined chirp rate, and discarded 50% of the power. However CPI has better resolution than OCT, automatic dispersion cancellation, and 10,000,000 times the signal strength of QOCT [13]. A new, much more flexible and efficient method of CPI will be demonstrated by creating the frequency correlations entirely in a single pulse. This new method is referred to as non- linear chirped pulse interferometry (NL-CPI). The non-linear chirp required in NCPI is very difficult to produce using only conven- tional optics. In this thesis we document the construction and characterization of a new method of creating the desired chirp using a programmable pulse-shaper (PS). We build a PPS and then demonstrated its functionality by compressing a 105nm FWHM bandwidth pulse to under 17f s, near its transform limited time duration. We also show that the values given to the PPS for dispersion are accurate by calculating and then compensating the dispersion caused by various optical elements in the CPI interferometer. Conventional OCT systems are immune to dispersion common to both arms of the interferometer. Non-linear interferometers experience broadening due to this dispersion, making them more difficult to use with fibre based interferometers common in conventional OCT. We show that NL-CPI can compensate for dispersion common to both arms of the interferometer, making NL-CPI more appealing as a replacement for conventional OCT. In this thesis we experimentally implement and demonstrate a prototype setup using non-linear CPI for dispersion-cancelled imaging of a mirror, with a resolution comparable to conventional OCT systems. We then use the system to produce 2-D cross sectional images of a biological sample, an onion. Q-OCT has previously been used to image an onion[16], but required treating the onion with gold nano particles to achieve a useful signal. The onion we used had no special treatment. In addition our axial scanning rate is also 10000 times faster than Q-OCT.

Biomedical imaging requires high resolution to see the fine features of a sample and fast acquisition to observe live cells that move. Optical coherence tomography (OCT) is a powerful technique which uses optical interference for non-invasive high resolution 3D imaging in biological samples. The resolution of OCT is determined by the length over which the light used will in- terfere. Unfortunately, dispersion hurts the imaging resolution by broadening interference features. A technique called quantum-OCT (QOCT)[1] is immune to dispersion but re- quires entangled photon pairs. The need for entanglement drastically reduces the number of photons available for imaging, making QOCT too slow to be practical. Chirped-pulse interferometry (CPI) is also immune to dispersion. A chirped pulse is one where the fre- quency, or colour, of the light changes from red to blue from one end of the pulse to the other. CPI relies on frequency correlations created by applying different chirps to two sep- arate pulses. This method had the disadvantage of being limited to a single predetermined chirp rate, and discarded 50% of the power. However CPI has better resolution than OCT, automatic dispersion cancellation, and 10,000,000 times the signal strength of QOCT [13]. A new, much more flexible and efficient method of CPI will be demonstrated by creating the frequency correlations entirely in a single pulse. This new method is referred to as non- linear chirped pulse interferometry (NL-CPI). The non-linear chirp required in NCPI is very difficult to produce using only conven- tional optics. In this thesis we document the construction and characterization of a new method of creating the desired chirp using a programmable pulse-shaper (PS). We build a PPS and then demonstrated its functionality by compressing a 105nm FWHM bandwidth pulse to under 17f s, near its transform limited time duration. We also show that the values given to the PPS for dispersion are accurate by calculating and then compensating the dispersion caused by various optical elements in the CPI interferometer. Conventional OCT systems are immune to dispersion common to both arms of the interferometer. Non-linear interferometers experience broadening due to this dispersion, making them more difficult to use with fibre based interferometers common in conventional OCT. We show that NL-CPI can compensate for dispersion common to both arms of the interferometer, making NL-CPI more appealing as a replacement for conventional OCT. In this thesis we experimentally implement and demonstrate a prototype setup using non-linear CPI for dispersion-cancelled imaging of a mirror, with a resolution comparable to conventional OCT systems. We then use the system to produce 2-D cross sectional images of a biological sample, an onion. Q-OCT has previously been used to image an onion[16], but required treating the onion with gold nano particles to achieve a useful signal. The onion we used had no special treatment. In addition our axial scanning rate is also 10000 times faster than Q-OCT.

In some high-field laser-plasma experiments, it is advantageous to accompany the main high-energy (~1 J) laser with a second high-energy pulse (~0.1 J) which has been frequency-shifted by ~10-20%. Such a pulse-pair would have a low walk-off velocity while remaining spectrally distinct for use in two-color pump-probe experiments. Moreover, by shifting the second pulse by ~plasma frequency, it is theoretically possible to exercise some amount of control over a variety of laser-plasma instabilities, including forward Raman scattering, electromagnetic cascading, and relativistic self-focusing. Alternatively, the two pulses may be counter-propagated so that the collide in the plasma and create a slowly-propagating beatwave which can be used to inject electrons into a laser wakefield accelerator. The design, characeterization, and performance of a hybrid chirped-pulse Raman amplifier (CPRA)/Ti-Sapphire amplifier are reported and discussed. This hybrid system allows for the generation of a high-energy (>200 mJ), broadband (15-20 nm bandwidth FWHM), short duration (>100 fs duration) laser sideband. When amplified and compressed, the Raman beam's power exceeds 1 TW. This sideband is combined with the primary laser system to create a bi-color terawatt laser system which is capable of performing two-color high-field experiments. This two-color capability can be added to any commercial terawatt laser system without compromising the energy, duration or beam quality of the primary system. Preliminary two-color laser-plasma experiments are also discussed. / text

<div>The chemical complexity of hydrocarbon fuels and the fast-expanding list of potential plantderived biofuels pose a challenge to the scientific community seeking to provide a molecular understanding of their combustion. More refined spectroscopic tools and methodologies must be developed to selectively detect and characterize the widening array of fuel components and combustion reactive intermediates. The direct relationship between molecular structure and rotational frequencies makes rotational spectroscopy highly structural specific; therefore, it offers a powerful means of characterizing pyrolysis ntermediates. This thesis describes experimental work using broadband microwave spectroscopy to address a number of challenging problems in the spectroscopy of gas complex mixtures.</div><div><br></div><div>Usually, the observed rotational spectra contain contributions from many distinct species, creating a complicated spectrum with interleaved transitions that make spectral assignment challenging. To assist with the process, a protocol called “strong-field coherence breaking” (SFCB) has been developed. It exploits multi-resonance effects that accompany sweeping the microwave radiation under strong-field conditions to output a set of transitions that can confidently be assigned to a single component in a mixture, thereby reducing the spectral assignment time.</div><div><br></div><div>The broadband chirped pulse Fourier transform microwave (CP-FTMW) spectra of guaiacol, syringol, 4-methyl guaiacol, 4-vinyl guaiacol were recorded under jet- cooled conditions over the 2-18 GHz frequency range. Using data from the 13C isotopomers the r0 structure of guaiacol was determined by means of a Kraitchman analysis. The tunneling due to OH hindered rotation was observed in syringol and the V2 barrier was deduced to be 50% greater than phenol’s barrier. This is due to the intramolecular H-bonding between the hydroxy and the methoxy groups. The internal rotation barrier for the methyl group for 4-methyl guaiacol was also determined. Moreover, the spectral assignment of the two conformers of 4-vinyl guaiacol was sped-up by using SFCB. The main structural insight from these lignin-related molecules was that polar substituents dictate the magnitude and type of structural shift that occurs relative to that of the unsubstituted aromatic ring.</div><div><br></div><div>In the next part of my work, the pyrolysis of 2-methoxy furan was carried out over the 300-1600 K temperature range, with microwave detection in the 2-18 GHz frequency range, using hightemperature flash pyrolysis micro-reactor coupled with a supersonic expansion. The SFCB technique was used to analyze and speed up the line assignment. The 2-furanyloxy radical, a primary, resonance-stabilized radical formed by loss of a methyl group in the pyrolysis of 2-methoxy furan, was detected and its molecular parameters were determined.</div><div><br></div><div>Finally, a unique setup that combines the high-resolution spectroscopic data provided by chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy with photoionization mass spectra from a vacuum ultraviolet (VUV) time-of-flight mass spectrometer (TOF-MS) was used to find optimal conditions to detect reactive intermediates and make full assignments for the microwave spectra of phenoxy radical and o-hydroxy phenoxy radical over the 2-18 GHz range. Phenoxy radical was generated through the pyrolysis of anisole and allyl phenyl ether. Using a combination of data from 13C isotopomers and fully deuterated phenoxy radical, in combination with high level ab initio calculations, a near-complete r0 structure for the radical was obtained. The structural data point to the radical being a primarily carbon-centered rather than oxygencentered radical. Using guaiacol as precursor, we studied the spectroscopy of the o-hydroxy phenoxy radical, whose structural data is compared with that of phenoxy to understand the role played by the hydroxyl group in modifying the resonance stabilization of the radical.</div><div><br></div>

In the laser market, there have been various kinds of lasers designed and utilized for different purposes. As time goes on, their powers have been gradually increased from kilowatts (kW) to terawatts (TW). One of the most famous methods in laser science technology is Chirped Pulse Amplification (CPA) which enables table-top terawatt laser systems. This method provides high output power (tens of TW), very short pulse duration (few tens of femtoseconds) and large energy (mJ) for ultrafast lasers. One of the most well-known ultrafast lasers is Titanium:Sapphire laser. This thesis work concentrates on how delay a pulse generator should work so that Verdi and the oscillator pulse coincide. Moreover, by assembling a terawatt laser system, the most important issues are timing between seed pulse and pump pulse and time delays of all components of this system / autocorrelator, pump source, photodiode, Pockels cell, stretcher and dazzler were examined. This timing and the time delays were separately identified for terawatt laser systems. In this study, the aim is to attain the terawatt level output by arranging pump and seed pulses timing and the time delay on the components of the laser system setup.