PhD Thesis Defense

In the more than 60 years since the invention of the laser, complementary developments in nonlinear and ultrafast optics have revolutionized fundamental science and technology, enabling the measurement of atomic and electronic motion at their native timescales, optical timekeeping with unprecedented precision, information processing offering speeds beyond those attainable in electronics, and novel spectroscopy and sensing techniques capable of parallel detection of several analytes with fast acquisition times and high sensitivity. On the one hand, pulsed sources are particularly well-suited for driving nonlinear phenomena, as the strength of nonlinear interaction depends on the peak power of the optical input. Conversely, spectral broadening, pulse shaping, and temporal sampling mechanisms enabled by nonlinearity have been critical in developing ultrafast sources and systems.

In this thesis, we further explore this synergistic relationship between nonlinear and ultrafast optics. We specifically study nonlinear dynamical phenomena such as soliton formation and supercontinuum generation in parametric amplifiers and oscillators exhibiting a quadratic (χ(2)) nonlinearity, and we show how these processes can be leveraged for the efficient generation of ultrashort pulses and coherent broadband spectra, with direct application in sensing and information processing. We begin by exploring the formation of mid-infrared temporal simultons in a free-space optical parametric oscillator, and we exploit their formation dynamics for enhanced molecular sensing. Next, we turn to the thin-film lithium niobate platform and demonstrate pJ pulse energy, two-color soliton pulse compression to the two-cycle regime in a dispersion-engineered waveguide. We additionally show that the strong nonlinearity in such waveguides enables the on-chip characterization of ultrashort, ultra-weak pulses. Next, we demonstrate a coherent, multi-octave frequency comb from a far-above-threshold nanophotonic parametric oscillator and investigate the dynamics underpinning its formation. Finally, we show simultaneous oscillation of 70 independent time-multiplexed parametric oscillators in a dispersion-engineered nanophotonic cavity. Our results pave the way to a new generation of scalable and efficient ultrafast sources, sensors, and information processing systems powered by quadratic nonlinearity.