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Item Sub-micron auger electron spectroscopy characterization of lithium niobate ferroelectric domains and their fabrication(Montana State University - Bozeman, College of Letters & Science, 2022) McLoughlin, Torrey John; Chairperson, Graduate Committee: Wm. Randall Babbitt; This is a manuscript style paper that includes co-authored chapters.Ferroelectrics are a novel class of materials with a built-in electric polarization state. Like ferromagnetic materials, by applying a strong external field, the direction of ferroelectric polarization can be switched, or 'poled'. Poling also switches the sign of the nonlinear coefficient, which determines the strength of a material's nonlinear optical interactions. By controlling the ferroelectric poled domain structures, the switching sign of the nonlinear coefficient can keep interacting optical waves in-phase, limiting deleterious material dispersion during nonlinear optical interactions. Lithium niobate (LiNbO 3) is one such ferroelectric crystal, prominently used in nonlinear optics. Periodically poled lithium niobate (PPLN) domain structures can produce the phase-matching conditions described above in a process called quasi-phase matching, creating powerful nonlinear optical devices. The applications of these devices are numerous, yet they have not reached their full potential due to the limitations of fabricating and characterizing nano-scale patterned domain structures. We first explored nano-fabrication of electrodes as a precursor to nano-scale poling. Periodic grating electrodes with 600 nm periods were fabricated using an innovative combined photolithography and electron beam lithography (EBL) liftoff method to create HV poling contact electrodes. A 10 kV bulk poling system was built and preliminary poling tests in three distinct poling configurations were performed on magnesium-doped lithium niobate (MgLN). We then adapted Auger electron spectroscopy (AES) as a new method to address the unique challenge of characterizing ferroelectric domains. In our initial AES characterization method, polar ferroelectric domains (+/-Z directions) in MgLN were differentiated from one another by the Auger O-KLL peak energy, with the -Z domains having higher peak energy due to the lower surface potential. We then discovered that +/-Z domains in PPLN can be differentiated with nano-scale resolution by the O-KLL peak amplitude, which is larger for -Z domains. The principle of this AES peak amplitude separation method was applied to mapping to achieve full imaging of PPLN's +/-Z domains with fields of view spanning from 7.5-200 microns. We ultimately demonstrate AES mapping as a new lithium niobate domain imaging method that is non-destructive, non-contact, unambiguous, with nano-scale resolution down to 67 nm.Item Quantitative multiphoton absorption spectroscopy(Montana State University - Bozeman, College of Letters & Science, 2018) Mikhaylov, Alexander Evgen'evich; Chairperson, Graduate Committee: Aleksander RebaneMultiphoton absorption (MPA) is an intriguing photophysical process that has been found useful for diverse areas of science. Low probabilities of MPA processes in molecular systems require to use intense photon fluxes that can be generated by femtosecond laser sources. Performing MPA measurements with sufficient precision requires a detailed characterization of the photon flux values that poses many technical difficulties. However, if the MPA values are determined accurately, then a quantitative analysis of the data obtained can be used to derive information about many important molecular parameters. As an example of MPA spectroscopy we discuss here two-photon absorption (2PA) methods. 2PA spectroscopy is applied to elucidate the structure-property relationships in different types of molecular systems including Pt-based chromophores, pyrrolo-pyrol complexes, organometallic ferrocene compounds, porphyrin oligomers and DNA base fluorescent analogs. Such spectroscopic analysis allows to shed some light on questions of inversion symmetry breaking effects and charge transfer on molecular scales. The measured 2PA spectra are also used to test several approximations for 2PA cross section expressions by comparing the values of molecular parameters derived from the measured 2PA data with other methods and literature data. We employ different experimental methods including two-photon excited fluorescence and nonlinear transmittance to measure 2PA spectra in a broad range of excitation wavelengths. The success achieved with 2PA based methods stimulates interest in three-photon absorption (3PA) measurements. We report on a progress achieved in 3PA measurements using three-photon excited fluorescence. This method is used to measure 3PA spectra of common fluorescent standards including Fluorescein and Rhodamine 6G and other organic dyes in different solvents. Effects of third harmonic generation and solvents absorption are discussed concerning the reliability of the 3PA measurements.Item Nonlinear correction of spectrally recovered, RF spectral features, readout with high frequency-chirped laser fields(Montana State University - Bozeman, College of Letters & Science, 2017) Oberto, Louis Joseph; Chairperson, Graduate Committee: Wm. Randall BabbittFrequency-chirped readout of spectral features from spatial-spectral (S2) materials, as a result of spectral hole-burning, has been in use as a radio-frequency (RF) spectrum analyzer for well over a decade. Previously, a signal processing deconvolution algorithm had been developed that enabled faster chirping, such that the chirp rate 'K' could be much greater than the desired resolution bandwidth (RBW). This broke past conventional limits for spectroscopic detection, which states that one needs to dwell on a spectral feature of width gamma for a time 1/gamma. For a chirp, this would mean that the square root of the chirp rate would need to be less than the RBW. For chirp rates on the order of gamma 2 or higher, nonlinearities begin to appear in detected signals depending on optical absorption depth, the chirp rate, and burned hole depths. Even with this algorithm, distortions still persist when very deep holes are burned in a high absorbing material, while the chirp rate is still very high. However, resolving spectral features under these conditions is desirable to increase the dynamic range of the SA. A new nonlinear signal processing technique that removes the nonlinearity has been developed, recovering the distorted signals. It was applied to RF signals spectrally absorbed in two different Tm 3+: YAG crystals, with measured absorption lengths of 1.9 and 2.5. The new algorithm is shown to work on multiple spectral holes simultaneously. Signals as wide as 1 MHz and as small as 300 kHz were recovered for a chirp rate of about 11.88 MHz/microsecond. These results show that very fast chirp rates could be used for highly absorbing materials, with deeply burned spectral holes. This could enable ultra-sensitive readout of a spectrum spanning hundreds of gigahertz, while pushing the dynamic range higher.Item Gain and index guiding effects in an injection seeded Raman amplifier(Montana State University - Bozeman, College of Letters & Science, 1996) Repasky, Kevin ScotItem Oxidation of N:Al(110)(Montana State University - Bozeman, College of Letters & Science, 1990) Brown, Wade WilliamItem Doubly-resonant two-photon-absorption-induced four-wave mixing in Tb(OH)₃and LiTbF₄(Montana State University - Bozeman, College of Letters & Science, 1982) Ender, David AdamsItem Simultaneous two-photon absorption of tetrapyrrolic molecules : from femtosecond coherence experiments to photodynamic therapy(Montana State University - Bozeman, College of Letters & Science, 2003) Karotki, Aliaksandr; Chairperson, Graduate Committee: Aleksander Rebane; Rufus L. Cone (co-chair)Simultaneous two-photon absorption (TPA) in tetrapyrrolic molecules is studied and its applications to two-photon coherence gratings and singlet oxygen generation for photodynamic therapy are demonstrated in this thesis. First ever comprehensive study of TPA properties of tetrapyrrolic molecules is conducted in this work. Two-photon transitions in two key spectral regions, red to green and blue to near-UV (transition wavelengths) are investigated. Physical mechanisms leading to enhancement of TPA cross section in tetrapyrroles are elucidated. Porphyrin molecules with greatly enhanced two-photon cross sections are obtained. Spectral coherence interference gratings are created by means of two-photon excitation with pairs of phase-locked femtosecond pulses in tetrapyrrolic molecules. First, gratings are detected by means of persistent spectral hole burning, which constitutes the first ever demonstration of spectral hole burning by simultaneous absorption of two photons. Next, the gratings are detected in fluorescence spectrum, which we use to study zero-phonon lines and phonon sidebands in two-photon transitions. Application of tetrapyrrolic molecules to two-photon photosensitization of singlet molecular oxygen is investigated. First, TPA properties of some known one-photon photosensitizers are investigated. Then, a new class of TPA based photosensitizers with greatly enhanced two-photon cross sections is developed. The generation of singlet molecular oxygen upon two-photon excitation of the new photosensitizers demonstrated for the first time, which opens up new perspectives for two-photon photodynamic therapy