Browsing by Author "Lee, Siu Au, committee member"
Now showing 1 - 12 of 12
Results Per Page
Sort Options
Item Open Access A measurement of muon neutrino charged-current interactions with a charged pion in the final state using the NOνA near detector(Colorado State University. Libraries, 2023) Rojas, Paul Nelson, author; Buchanan, Norm, advisor; Lee, Siu Au, committee member; Harton, John, committee member; Kokoszka, Piotr, committee memberThe NOνA experiment is a long-baseline neutrino experiment hosted by Fermilab. The intense NuMI neutrino beam, combined with NOνA Near Detector, provides the opportunity to study neutrino interactions at an unprecedented level. The goal of this analysis is to measure the rate of muon-neutrino charged-current interactions in the NOνA near detector resulting in the production of one muon and at least one charged pion. This thesis will present the result of the double differential cross section measurement of this process in muon kinematics of energy and angle. Excesses in the extracted signal (greater than 25%), relative to the simulation, were found at large scattering angles. These excesses were greater than the estimated uncertainties (∼15%).Item Open Access Advancing the capability of high energy Yb:YAG lasers: multilayer coatings, pulse shaping and post compression(Colorado State University. Libraries, 2022) Wang, Hanchen, author; Rocca, Jorge, advisor; Roberts, Jacob, committee member; Lee, Siu Au, committee member; Marconi, Mario, committee memberRecently, cryogenically cooled Yb-doped amplifiers have been successfully scaled both in output energy and in repetition rate. The performance of such laser systems and their applications can be expanded by advancements in the development of optical coatings, that allow for scaling to higher pulse energies; as well as improvements in pulse shaping that include shorter pulse durations and the generation of programmable sequences of ultrashort pulses. This dissertation focuses on realizing the improvements mentioned above for cryogenic Yb:YAG amplifiers. First it reports the evaluation of ion beam sputtering (IBS) dielectric coatings for Yb:YAG at the environmental conditions in which cryogenic amplifiers are operated. The IBS coatings showed consistent performance in ambient, vacuum and cryogenic conditions, with damage threshold measured 20.4±0.6 J/cm2 for anti-reflection (AR) coating, and 27.4±1.3 J/cm2 for high reflector (HR) coating with 280 ps pulse duration at 77 K under the ISO:21254 standard. Second, a method for synthesizing trains of high energy compressed pulses was demonstrated and used to pump an 18.9 nm Ni-like Mo plasma-based soft x-ray laser more efficiently. The synthesized pulse increased the conversion efficiency of this spatially coherent soft x-ray source by 40%. Finally, femtosecond pulses were generated by post compression using a gas filled hollow core fiber (HCF), in which spectral broadening was achieved by self-phase modulation with an additional contribution from stimulated Raman scattering. Utilizing nitrogen gas as the non-liner medium, 300 mJ, 8 ps pulses were broadened to 3.7 nm and re-compressed to 460 fs by a grating compressor. The propagation and spectral broadening of high energy picosecond pulses in gas-filled HCFs were modeled and the results of simulations were compared with experiments.Item Open Access Detection of small numbers of barium ions implanted in solid xenon for the EXO experiment(Colorado State University. Libraries, 2012) Cook, Shon, author; Fairbank, William, advisor; Lee, Siu Au, committee member; Roberts, Jacob, committee member; Bartels, Randy, committee memberIn an effort to discover the yet-unknown absolute masses of neutrinos, the goal of the Enriched Xenon Observatory is to observe neutrinoless double beta decay of 136Xe. Identification of this very rare decay may be difficult even with the best conventional efforts to reduce and reject radioactive background, thus requiring additional background rejection via detection of the daughter 136Ba nucleus. One method of detection is laser-induced fluorescence of the barium atom in solid xenon. Spectra of very small numbers of barium atoms in solid xenon, as few as 3 atoms, are reported for the first time. Demonstration of detection of Ba atoms with large fluorescence efficiencies gives promise for detecting single atoms in the near future. Results from experiments involving implantation of Ba+ ions in solid xenon are discussed. One narrow excitation peak was discovered from ion beam deposition that was not found in neutral deposits. Five new emission lines are found with this same excitation spectrum. Bleaching, annealing, and laser dependence of these lines are studied. The identification of the new Ba species as Ba+ or as a barium molecule is discussed.Item Open Access Development of a high energy TI:Sapphire laser for the excitation of extreme ultraviolet lasers(Colorado State University. Libraries, 2011) Martz, Dale Herman, author; Rocca, Jorge J., advisor; Lee, Siu Au, committee member; Menoni, Carmen S., committee member; Marconi, Mario C., committee memberThis dissertation describes the design, construction and characterization of a high energy chirped-pulse amplification Titanium-Sapphire laser system for the excitation of Extreme Ultraviolet (EUV) lasers. Compact EUV lasers have made possible nano-scale imaging, dense plasma diagnostics and photo-chemistry and photo-physics studies. They also have the potential to make possible a variety of new studies of surfaces and materials and enable the development of unique metrology and processing tools for industry. The components developed to realize high energy operation of the Titanium-Sapphire laser include the development of a Nd:Glass zig-zag slab pump laser and novel 800 nm multi-layer dielectric diffraction gratings for picosecond compression. The Titanium-Sapphire laser was used to pump several table-top EUV lasers. Increased average power operation of a 13.9 nm nickel-like silver laser generating 20 uW was demonstrated. This is the highest average power obtained from a compact EUV laser to date. Injection seeding of the 13.9 nm EUV amplifier produced laser beams with greatly improved beam characteristics which includes a large reduction in beam divergence and a near Gaussian far-field profile. The laser was also used to pump a gain-saturated table-top laser at 10.9 nm in nickel-like tellurium.Item Open Access Development of a high power chirped pulse amplification laser for driving secondary sources(Colorado State University. Libraries, 2019) Baumgarten, Cory M., author; Rocca, Jorge, advisor; Roberts, Jacob, committee member; Lee, Siu Au, committee member; Marconi, Mario, committee memberLaser applications which require high energy ultrashort laser pulses have been limited in repetition rate. This dissertation describes the development of high repetition rate, high energy, all diode pumped ultrashort pulse Yb:YAG lasers and their use in two selected applications. Yb:YAG is an attractive gain medium for high average power, ultrashort pulse laser operation. This material, with long upper level lifetime, is well suited for direct pumping by high power, narrow bandwidth laser diodes, and combined with a small quantum defect, minimal heating of the material is produced. Additionally, the thermal conductivity and optical properties of Yb:YAG dramatically improve when cooled to cryogenic temperatures. The main focus of this dissertation is the development of an all diode-pumped, chirped pulse amplification, ultrashort pulse laser based on a cryogenically-cooled Yb:YAG amplifier design. This laser system operates at λ = 1.03 μm and is capable of producing 1.4 J pulses before compression at 500 Hz and 1 kHz repetition rate. During 500 Hz operation, the laser used a combination of room temperature and cryogenically-cooled Yb:YAG amplifiers to generate pulses of 1 J energy compressed to sub- 5ps duration. At 1 kHz, pulse energies of 1 J with sub-10ps transform limited pulse durations were obtained. The simultaneously high pulse energies and repetition rates obtained in this work will be beneficial for a host of applications including tabletop sources of coherent short wavelength radiation, high power femtosecond sources operating in the near and mid-infrared, and high gradient laser plasma accelerators. The work in this dissertation specifically demonstrates the use of cryogenically cooled Yb:YAG lasers in the development of soft x-ray lasers and a near-infrared optical parametric amplifier for the testing damage threshold of multilayer coatings.The generation of coherent radiation in the soft x-ray regime was historically limited to 10 Hz. Compact, table-top soft x-ray lasers have enabled a range of applications including nano- scale imaging and lithography, the investigation of hot dense plasmas, and nano-scale fabrication. Recently, compact sources of coherent soft x-ray laser radiation were demonstrated at repetition rates of one hundred shots per second using the laser technology described in this dissertation. As a demonstration of the Yb:YAG laser's excellent beam quality and high average power, this system was used to pump a high repetition rate soft x-ray laser. The optical pump laser and the resulting soft x-ray laser, operated at a record 400 Hz repetition rate with strong lasing in the λ = 18.9 nm line of Ni-like Mo. This work also demonstrates a Yb:YAG laser driven, optical parametric chirped pulse amplification (OPCPA) laser system operating at 100 Hz in the near-infrared, which was used to per- form laser induced damage threshold measurements of optical coatings. OPCPAs have emerged as a next generation ultrafast laser source for generating sub-femtosecond laser pulses useful for probing molecular electron dynamics as well as creating ultra-intense, femtosecond laser pulses for exploring exotic states of matter and for the development of next generation laser plasma accelerators. The OPCPA developed as part of this work operates at wavelengths ranging from λ = 1.5-2 μm with final amplification stages pumped at 100 Hz with a chirped pulse amplification laser based on cryogenically-cooled Yb:YAG. The OPCPA was used to obtain damage thresholds of optical coatings in what to our knowledge constitutes the first results of picosecond damage performed in this wavelength range.Item Open Access Development of a high power high energy ultrafast laser(Colorado State University. Libraries, 2021) Chi, Han, author; Rocca, Jorge, advisor; Menoni, Carmen, committee member; Marconi, Mario, committee member; Lee, Siu Au, committee memberThis dissertation describes the development of high energy, high repetition rate laser technology based on cryogenically cooled diode-pumped Yb:YAG laser amplifiers. The key challenges of thermal management, the generation of high energy green pulses at high repetition rate, and the design of an ultrafast laser amplifier that uses the green pulses as pump are discussed in this dissertation. To aid the development of thermal management solutions, an accurate, in situ, noninvasive optical technique to generate three-dimensional (3-D) temperature maps of cryogenic amplifiers during operation at high average power was demonstrated. The temperature is determined by analyzing the fluorescence spectra of the laser material (Yb:YAG) with a neural network algorithm. The accuracy of the technique relies on a calibration that does not depend on simulations. Results are presented for a cryogenic Yb:YAG active mirror laser amplifier operating at different pump conditions, which include kW pump power level operation. Based on this temperature measurement technique, an analysis of the thermal behavior of a high-energy kilowatt-average-power diode-pumped cryogenically cooled Yb:YAG active mirror laser amplifier is presented. Maps of the temperature distribution in the laser amplifier crystal at pump powers up to 1kW were obtained for the first time by spectrally resolving the fluorescence induced by a scanning probe beam. The cryo-temperature measurement technique is applicable to other solid-state lasers materials. The wavefront distortions resulting from the front surface deformation and the overall deformation of the gain medium assembly were measured using a Mach–Zehnder interferometer. The measured deformations agree well with the results of finite element thermomechanical modeling simulations, and with the results of focal length shift measurements. The relative contributions to the optical path difference (OPD) of the mechanical deformations, refractive index changes, and electronic contribution are discussed. The pump-induced mechanical deformations of the assembly dominate the OPD changes in the kilowatt-average-pump-power cryogenically cooled Yb:YAG active mirror laser investigated. The generation of green (λ= 515 nm) Joule-level pulses at 1 kHz repetition rate was demonstrated. This was achieved by frequency doubling 1.2 J, 2 ns temporally shaped square pulses from a cryogenically cooled Yb:YAG laser in an LBO crystal. The generation of 0.94 J second-harmonic pulses at 1 kHz was demonstrated with 78% conversion efficiency. The unconverted light was sent through a second LBO crystal to generate an additional >100 mJ second-harmonic pulses to reach a total green average power of 1.04kW. A higher conversion efficiency of 89% was also achieved for 0.58 J green pulses at 1 kHz. An application of this green laser is the pumping of high average power ultrafast laser amplifiers. The design of a two-stage water-cooled Ti:Sapphire amplifier system to generate 300 mJ pulses pre-compression using this green laser as pump is discussed. The simulation of the gain and thermal distribution of the 1st and 2nd stage amplifier are presented. The first experimental results of the operation of the first amplification stage of this laser system are discussed.Item Open Access Development of a petawatt class Ti:Sapphire laser for the excitation of extreme radiation sources(Colorado State University. Libraries, 2020) Rockwood, Alex Pratt, author; Rocca, Jorge J., advisor; Lee, Siu Au, committee member; Roberts, Jacob L., committee member; Marconi, Mario C., committee memberThis dissertation describes the design, construction and characterization of a high peak power, high repetition rate, Titanium-Sapphire laser system. This chirped-pulse amplification (CPA) laser delivers femtosecond pulses of up to 0.85 PW peak power. By utilizing pump laser amplifiers with a slab configuration high repetition rate are achieved, 3.3Hz, the highest at which Petawatt-class lasers have been operated to date. This 800nm laser also has a high power, ultra-high contrast 400 nm beamline. By frequency doubling the 800 nm with a KDP crystal at ≥ 40% conversion we are able to achieve a contrast of > 1 × 10-12. The ability to focus this second harmonic beam to ~1.2 μm Full Width at Half Maximum (FWHM) spot size made it possible to achieve intensities up to ~ 6.5 ×1021 W/cm2. With these high intensities and high contrast this laser is a powerful tool in many applications especially in the study of laser/matter interactions at relativistic plasmas. This Ti:Sapphire laser was used for the excitation of plasma based soft x-ray (SXR) lasers. prior to this work compact, repetitively fired, gain-saturated x-ray lasers had been limited to wavelengths above λ = 8.85 nm. We were able to demonstrate SXR lasers operating in the gain-saturated regime down to wavelengths as low as λ = 6.85 nm in Ni-like Gd. Gain was also observed at λ = 6.4 nm, and λ = 5.8 nm in Ni-like Dy. As an application of plasma-based SXR lasers, single shot Fourier holograms covering a large area of view were demonstrated using an 18.9nm laser with high spatial coherence based on dual plasma amplifier. Compact SXR lasers have made possible applications in nano-scale imaging, dense plasma diagnostics and a variety of new studies of materials and surfaces. Other applications that were enabled by this Petwatt-class laser discussed elsewhere include the study of the interaction of relativistic laser pulses with aligned nanostructures, producing record conversion efficiency of optical laser light into picosecond x-ray pulses with photons of > 1 KeV energy and flashes of deuterium-deuterium fusion neutrons.Item Open Access Gain-saturated repetetive soft X-ray lasers with wavelengths spanning 9-30 nm and lasing down to 7.4 nm(Colorado State University. Libraries, 2011) Alessi, David Alan, author; Rocca, Jorge J., advisor; Lee, Siu Au, committee member; Menoni, Carmen S., committee member; Marconi, Mario C., committee memberThis dissertation describes the development of table-top soft X-ray lasers with wavelengths ranging from 30 nm to 7.4 nm. The laser transisitons occur within collisionally excited states of nickel-like and neon-like ions which are created from laser ablation of solid targets. A Nd:glass slab laser system was developed to provide 20J (and then upgraded to 40J) of laser light at 527 nm for pumping a table-top chirped pulse amplification Ti:sapphire laser. With this increase in pump energy, the Ti:sapphire system is capable of producing 12J uncompressed laser pulses at a 1Hz repetition rate. Stretched and compressed pulses from this Ti:sapphire laser system operating near 800 nm are used to both ionize the material to a high degree and heat the free electrons in these plasmas to temperatures required for high gain. Simulations from a 1.5D hydrodynamic/atomic model indicate a peak gain of 90 cm-1 for the 8.8 nm laser transition in nickel-like lanthanum is reached with an electron temperature of ~850 eV and a density of 6×1020 cm-3. By using the grazing incidence pumping geometry, gain saturated operation was demonstrated in the 2p53p 1S0 →2p5 3s 1P1 transition of neon-like titanium (λ = 32.6 nm) and vanadium (λ = 30.4 nm), as well as in the 3d94d1S0→3d9 4p1P1 transition in nickel-like tellurium (λ = 10.9 nm) and lanthanum (λ = 8.8 nm). Strong lasing was also demonstrated in the same neon-like transition in chromium (λ = 28.6 nm), as well as the same nickel-like transition in cerium (λ = 8.5 nm), praseodymium (λ = 8.2 nm), neodymium (λ = 7.9 nm) and samarium (λ = 7.4 nm). This is the first demonstration of the generation of bright gain-saturated sub-9-nm wavelengths with a table-top laser operating at 1-Hz repetition rate. The short wavelength, microjoule pulse energy, picosecond pulse duration and repetitive operation of these lasers will enable new applications such as sequential imaging of ultrafast nano-scale dynamic phenomena to be realized on a table top.Item Open Access Imaging individual barium atoms in solid xenon by scanning of a focused laser for use in the nEXO experiment(Colorado State University. Libraries, 2019) Chambers, Christopher, author; Fairbank, William, advisor; Lee, Siu Au, committee member; Wilson, Robert J., committee member; Van Orden, Alan, committee memberNeutrinoless double beta decay (0νββ) is a non-standard model decay process in which two simultaneous beta decays occur, with no emission of neutrinos. This decay is of great interest. If observed, it will demonstrate that the neutrino and anti-neutrino are not distinct. This decay also violates lepton number conservation, a requirement for some theories seeking to explain the matter-antimatter asymmetry of the universe. A measurement of the decay half-life will also give information on the absolute mass scale of the neutrinos. EXO-200 and nEXO use liquid xenon (LXe) time projection chambers (TPC) to search for 0νββ decay. EXO-200 first observed two neutrino double beta decay (2νββ) in xenon-136, the rarest decay ever observed. A low background measurement is vital to maximizing sensitivity to the 0νββ decay mode, yet to be observed. In this dissertation, research and development of a technique for positive identification of the barium-136 daughter (barium tagging) is presented. It is desirable to incorporate barium tagging into the future nEXO detector, as it provides discrimination against all background except for the 2νββ decay mode. The scheme being developed in this work involves extraction of the barium daughter in solid xenon with a cryogenic probe, followed by matrix-isolation fluorescence spectroscopy to tag the barium atom. This work focuses on the detection of individual barium atoms in a prepared solid xenon sample. Single atom sensitivity has been achieved, and a method for imaging of individual atoms by scanning of a focused laser has been demonstrated.Item Open Access Modeling of laser-created plasmas and soft x-ray lasers(Colorado State University. Libraries, 2010) Berrill, Mark Allen, author; Rocca, Jorge J., advisor; Marconi, Mario C., committee member; Menoni, Carmen S., committee member; Lee, Siu Au, committee memberThis dissertation describes the development of computer models to simulate laser created plasmas used to generate soft x-ray lasers. These compact short wavelength lasers have substantial average powers and very high peak brightness, that make them of significant interest for many applications. A better understanding of the plasmas is necessary to advance the development of these lasers into more compact, efficient, and higher power sources of coherent soft x-ray light. The plasma phenomena involved are complex, and require a detailed computer model of the coupled magneto-hydrodynamic and atomic physics processes to simulate their behavior. The computer models developed as part of this work consist of hydrodynamic equations, coupled with an atomic model, radiation transport, and a ray propagation equation. The models solve the equations in a 1.5D or 2D approximation, and predict the spatio-temporal plasma variation of the parameter s, including the electron density and temperature, and the ion populations, which are then used to compute the population inversion and the resulting laser gain. A 3D post processor ray trace code was developed to simulate the amplification of stimulated emission along the plasma column length including saturation effects. This allows for the direct calculation of the soft x-ray laser output and its characteristics. Simulation results were compared with experiments conducted at Colorado State University. The general behavior of the plasma and the soft x-ray laser are well described by the model. A specific comparison of the model results with experimental measurements is presented for the case of a collisionally excited 13.2 nm wavelength Ni-like cadmium laser. The model predicts that an optical laser pulse of 1 J energy and 8 ps duration impinging at 23 degrees grazing incidence into a pre-created laser plasma can rapidly heat it to temperatures above 600 eV at a density of 2 x 1020 electrons/cm3. This results in a computed peak small signal gain coefficient of 150 cm-1 in the 4d 1S0 to 4p 1P1 transition of Ni-like Cd at 13.2 nm. The model indicates that the amplified beam reaches the gain-saturated regime after 2.5 mm of propagation in the plasma, in agreement with the experimental observation of saturated behavior for propagation lengths of 2.5-3.0 mm. The computed soft x-ray laser pulse width of 5-9 ps moderately exceeds the experimental value of 5 ps and is the result of a stronger saturation broadening in the simulation. The simulated laser output energy of the order of 1 μJ is also in agreement with experiments. Simulations of injection-seeded Ne-like Ti and Ni-like Ag amplifiers that show very good agreement with the experimental results are presented. A direct comparison of the pulsewidth and the near and far-field beam profiles is made. Finally, the results of a simulation of a plasma created by irradiation of solid targets with a 46.9 nm soft x-ray laser, in which single photon photoionization is the dominant energy absorption mechanism are presented. Low absorption (silicon, Z=14) and high absorption (chromium, Z=24) targets were heated by ~1 ns duration soft x-ray laser pulses. The experimental spectra agree with 1 ½ D simulations in showing that the Si plasmas are significantly colder and less ionized than the Cr plasma, confirming that in contrast to plasmas created by visible wavelength lasers the plasma properties are largely determined by the absorption coefficient of the target material.Item Embargo Molecular dynamics simulation studies and experimental measurements of radiofrequency heating for strongly coupled and extremely magnetized ultracold neutral plasmas(Colorado State University. Libraries, 2023) Jiang, Puchang, author; Roberts, Jacob L., advisor; Yost, Dylan, committee member; Lee, Siu Au, committee member; Yalin, Azer, committee memberUltracold neutral plasmas(UNPs) are good experimental platforms for fundamental plasma physics studies because of their experimentally adjustable parameters, accessible timescales, ability to enter the strong coupling parameter regime, and easy access to large degrees of electron magnetization. The work in this thesis contains both simulation and experimental studies of UNPs. One simulation project describes a new UNP heating mechanism discovered using Molecular Dynamics simulations: DC electric field heating. This DC electric field heating mechanism occurs when a DC electric field is present when the plasma is formed. sets a lower limit of how cold UNP electron temperatures can be reached experimentally. A second simulation project investigates a many-body physics effect on collisional damping in UNPs and a breakdown in standard plasma theory treatments when the plasma is approaching the strongly coupled regime. This breakdown arises due to the increasing significance of three- or many-body electron-ion interactions influencing the plasma transport properties and particle collisions. My simulations find evidence for this being the case. Experimental studies of UNP electron-ion collision physics during the application of high-frequency RF electric fields to the UNP were conducted, and measurements of the RF-induced electron heating rate from the weak magnetized regime to extremely magnetized regime were performed. The results obtained are in qualitative agreement with the theory prediction but there's quantitative disagreement. Possibilities for resolving this disagreement are presented.Item Open Access Spin multiplets: theory and application(Colorado State University. Libraries, 2018) Nite, Jacob M., author; Rappé, Anthony K., advisor; Shores, Matthew, committee member; Shi, Yian, committee member; Lee, Siu Au, committee memberTransition metal complexes have seen an increased use as photocatalysts for organic reactions in recent literature, mostly involving the Ru(II)(bpy)3 family of catalysts. Due to the rarity of ruthenium in the Earth's crust, alternative catalysts using Earth abundant materials are desirable. Recent literature has shown that chromium based catalysts show great promise as a replacement for ruthenium for some reactions. The mechanisms of these first-row transition metal complexes are significantly more complex than those of the second and third row. The excited state complexities of first-row transition metal complexes are challenges for both experimental and theoretical research. The complexities of the excited states require theoretical methods beyond the standard single reference methods commonly used in the literature. Through the use of recent multi-reference post Hartree Fock (HF) methods as well as a new multi-reference density functional theory (DFT), insights into the character of chromium-based photocatalysts were examined. A new multi-determinant DFT method named few-determinant density functional theory (FD-DFT) was described. FD-DFT incorporates multiple DFT determinants using a finite difference approach to calculate the exchanges between multiple determinants for open shell multiplets. The method is implemented in a generalized bond valence (GVB) wave function, and can be converged through an SCF procedure. The system was benchmarked using oxygen atom and diatomic oxygen as well as atomic systems with more open shell orbitals. The benchmarking shows stability across many different functional choices, and gives good excitation energies with and without SCF convergence. The Cr(III)(AcAc)3 system has been long studied for its unique excited state properties that defy the standard cascade model for excited state relaxation. The tris(1,3-propanedionato)chromium(iii) (Cr(III)(PDO)3) complex was studied as an analog to the Cr(III)(AcAc)3 system to understand the excited state pathway between the initial excited 4T2g state and the long lived 2Eg state. Using the FD-DFT method as well as the multi-reference spectroscopy oriented configuration interaction (SORCI) method, the initial excited state energies were studied compared to previous perturbation theory (PT) approaches. Both SORCI and FD-DFT calculate reasonable 2Eg excitation energies, an improvement over earlier results. The SORCI method was also used to map the potential energy curve between the initial 4T2g excited state and its fully relaxed distorted structure. The pathway agrees with previous experimental and theoretical studies showing that a transitionless path exists between the quartet and doublet states, but spin-orbit coupling calculations suggest that a direct path between the 4T2g and 2Eg is possible rather than needing a internal conversion step to the lowest 2Eg state. Chromium-based photocatalysts have been recently studied in the literature as having a competitive mechanism between the reaction substrate and O2 whereby the O2 quenches the excited catalyst. Using the combined Cr(III)(PDO)3 • O2 system, the likely states by which this quenching event occurs were studied with FD-DFT as well as recent multi-reference PT approaches. Comparing the excited state calculated using the multi-reference based methods to standards DFT calculations shows the inability of single-determinant methods to correctly produce the proper excited state character even when obtaining somewhat reasonable energies. The excited state responsible for the quenching of the excited complex is identified using spin density plots of the CASSCF calculations. The search for suitable first-row transition metals requires a search across possible ligands and metal centers. Using the success of chromium-based catalysts, isoelectronic vanadium catalysts were studied to identify any potential differences between the complexes as well as identify the utility of vanadium-based catalysts. Using a variety of methods, including TDDFT-based absorption spectra, vibrational component plots of the excited state distortions, and SORCI potential energy curves (PEC), the differences between the chromium and vanadium catalysts were examined. It was found that vanadium catalysts absorptions are shifted significantly from chromium complexes and the vanadium excited states disperse the unpaired electron over the complex instead of localizing it on the metal center. The distortions in the chromium-based catalysts have a greater amount of asymmetric vibrational character compared to vanadium, which shows mostly symmetric behavior. Lastly, the SORCI PECs show that, unlike chromium, the doublet curves do not intersect the quartet curves, making a transition to a long lived doublet state a significantly slower process. The results highlight significant differences between the complexes even with ligand structure is controlled.