Studies of third-order nonlinearities in materials and devices for ultrafast lasers

Abstract

Recent developments in telecommunications, frequency metrology, and medical imaging have motivated research in ultrafast optics. Demand exists for broadband components and sources as well as highly nonlinear fibers and materials. For this thesis, several different devices have been developed for such applications. Broadband saturable absorbers based on III/V and Si materials systems were developed for femtosecond lasers and have high reflectivity over 200 to 300 nm bandwidths. These absorbers were designed for modulation depths ranging from 0.3% to 18%. Self-starting modelocked operation with the absorbers was achieved in a variety of lasers including Ti:Sapphire, Cr:Forsterite, Er:glass, Cr⁴⁺:YAG and erbium-doped bismuth-oxide fiber. In tapered microstructure fiber, highly nondegenerate four-wave mixing was achieved, with a frequency shift of 6000 cm⁻¹ in an interaction length of only 1.4 cm. Amplification in erbium-doped bismuth-oxide fiber was demonstrated, with gains of 12 dB achieved between 1520 - 1600 nm in a 22.7-cm length. With a 55.6 cm length of bismuthoxide erbium-doped fiber, an L-band modelocked laser was constructed, tunable between 1570 - 1600 nm. It produced 288-fs pulses at 1600 nm. Undoped highly nonlinear bismuthoxide fiber was used to generate smooth, controlled supercontinuum between 1200 to 1800 nm.

(cont.) Pulse compression of 150-fs pulses to 25 fs was also demonstrated. Finally, the nonlinear refractive index coefficient and two-photon absorption coefficient of Ge-As-Se glasses were measured. Ge₃₅As₁₅Se₅₀ is found to have a nonlinearity 900 times that of silica.