Cascaded nonlinearities for ultrafast nonlinear optical science and applications

Research output: Book/ReportDoctoral thesis

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Abstract

Cascaded nonlinearities in quadratic nonlinear crystals underlie an immensely powerful control over the ultrafast nonlinear response, where it is possible at will to change the sign
of the nonlinearity and tune its strength seamlessly from weak to extremely strong. Here the physics behind the cascading nonlinearity is investigated in detail, especially with
focus on femtosecond energetic laser pulses being subjected to this nonlinear response. Analytical, numerical and experimental results are used to understand the cascading interaction and applications are demonstrated. The defocusing soliton is of particular interest here, since it is quite unique and provides the solution to a number of standing challenges in the ultrafast nonlinear optics community. It solves the problem of catastrophic focusing and formation of a filaments in bulk glasses, which even under controlled circumstances is limited to energies of a few µJ. In contrast, the defocusing soliton can sustain orders of magnitude larger energies. It also solves the challenge of using mature
near-IR laser technology to generate ultrashort, coherent and bright mid-IR radiation. The defocusing nonlinear effect that leads to intriguing observations with analogies in fiber
optics are observed numerically and experimentally, including soliton self-compression, soliton-induced resonant radiation, supercontinuum generation, optical wavebreaking and
shock-front formation. All this happens despite no waveguide being present, thanks to the defocusing nonlinearity. Finally, the richness of the complex nonlinear system is immense, and as an example the first observation of parametrically tunable resonant radiation is shown, phase-matched to the defocusing soliton, and emitted in the mid-IR and the visible/near-IR.
Original languageEnglish
PublisherDTU - Department of Photonics Engineering
Number of pages130
ISBN (Print)978-87-93089-99-0
Publication statusPublished - 2017

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