Solid-state laser mode-locking and ultrafast studies in quantum semiconductor structures

Abstract

This dissertation describes the development of ultra-short pulse solid-state lasers and the investigation of ultra-short pulse propagation in a nonlinear waveguide. We present laser design considerations involving astigmatism compensation, spot-size estimation, stability, and dispersion compensation, and their application to chromium doped forsterite lasers. Making use of the Kerr nonlinearity of the Cr:forsterite crystal we demonstrate self-mode-locking in Cr:forsterite lasers, both in the hard-aperture and soft-aperture Kerr-lens mode-locking regimes. Sub-200-fs pulses tunable between 1240 and 1285 nm were obtained, with the shortest transform-limited pulses having 45 fs duration at 90 MHz repetition rate with 100 mW output power at 1265 nm. Using a semiconductor quantum-well saturable absorber integrated with a Bragg reflector we demonstrated self-starting passive continuous-wave mode-locked operation of a Cr:forsterite laser. Self-starting mode-locking was the only operational mode of the laser and could be achieved with and without intracavity dispersion compensation. We obtained 70 fs transformed-limited pulses using a prism pair for dispersion compensation, 4 ps pulses without prisms, and pulse energies of up to 2.3 nJ at 90 MHz repetition rate at 1260 nm. Using quantum-confined nanocrystals of lead sulfide in glass as intracavity saturable absorbers we obtained self-starting passive continuous-wave mode-locking in a Cr:forsterite laser. We obtained near transform-limited 4.6 ps laser pulses at 100 MHz repetition rate, and a wide tunability range of 1207 to 1307 nm. We studied femtosecond pulse propagation near a two-photon transition in CdS quantum-dot-doped waveguides produced by the solgel and ion-exchange methods. The observed two-photon absorption and asymmetric spectral modulation of the transmitted pulses were explained by the theoretical model, which incorporated a near-resonant two-photon transition.