Mid-infrared (MIR) laser sources have demonstrated diverse applications in science and technology. For spectroscopy applications, numerous molecules have unique absorption features in this range, and one needs a spectrally broad coherent laser source for parallel detection of mixtures of species. Frequency down-conversion in nonlinear optical materials via second-order nonlinear susceptibility is one of the promising techniques to generate the spectral coverage of more than an octave in the MIR, assisted by emerging novel crystals. The nonlinear light-matter interactions in such special crystals as ZnSe ceramics have not been analyzed. Additionally, through the use of high-intensity few-cycle optical pulses, high-order nonlinear effects such as four-wave mixing, multiphoton absorption, and nonlinear refraction come into play beyond conventional second-order nonlinear interaction. In this thesis, the nonlinear interactions for generating broadband MIR were studied through both experimental and numerical approaches. First, a nonlinear frequency conversion model based on random phase matching was developed in zinc-blende polycrystalline structures. Monte Carlo simulation statistically verifies that a disordered material could perform on par with a quasi-phase-matched material for frequency conversion in ultrafast interactions. Second, the nonlinear interaction in orientation-patterned GaP combined with an optical parametric oscillator was numerically analyzed. A wave propagation model discovers that third-order nonlinearity plays an important role in the process of spectral evolution. Finally, using a 2.35-µm Cr:ZnS mode-locked laser, nonlinear absorption and nonlinear refractive index were characterized in the Z-scan technique for GaP, ZnSe, GaSe, and ZGP crystals. The visualization of nonlinear interactions and the uncovering of nonlinear parameters will be a guide for optimizing experimental systems and will further advance the development of MIR laser sources.
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Doctor of Philosophy (Ph.D.)
College of Optics and Photonics
Optics and Photonics
Optics and Photonics
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Kawamori, Taiki, "Nonlinear Light-matter Interactions in Novel Crystals for Broadband Mid-infrared Generation" (2021). Electronic Theses and Dissertations, 2020-. 887.