P. F. Curley

Kerr lens mode locking

Self-focusing in conjunction with an intracavity aperture creates a power-dependent amplitude modulation in laser oscillators, which allows passive mode locking. A simple analytical formalism yields closed-form expressions for the depth of passive amplitude modulation introduced by either the spatial gain profile or a hard aperture inserted in the resonator. Design issues for this mode-locking technique are discussed.

Operation of a femtosecond Ti:sapphire solitary laser in the vicinity of zero group-delay dispersion

We report the operating characteristics of a self-mode-locked Ti:sapphire solitary laser at reduced group-delay dispersion. The generation of asymptotically equal to 12.3 fs near-sech(2) optical pulses at 775 nm is reported, together with experimental evidence for the dominant role of third-order dispersion (TOD) as a limiting factor to further pulse shortening in the oscillator. At reduced second-order dispersion excessive residual TOD is shown to lead to dispersive wave generation, and the position of the dispersive resonance is used to determine the ratio of the net second- and third-order intracavity dispersions. Since the magnitude of TOD rapidly decreases with increasing wavelength in prism-pair dispersion-compensated resonators, the oscillator presented has the potential for producing sub-10-fs pulses in the 800-nm wavelength region.

Hard-aperture Kerr-lens mode locking

Self-focusing by a Kerr nonlinearity in combination with an intracavity aperture creates a power-dependent loss in lasers, which has been used as a method for passive mode locking of lasers. An analytical treatment is presented that yields closed-form expressions for the modulation efficiency. Comparisons between analytical results and numerical calculations are performed. General features of this mode-locking technique are discussed, and a procedure for the optimization of hard-aperture Kerr-lens mode-locking performance is given.

Coherent effects in a self-mode-locked Ti:sapphire laser.

The spectral and temporal characteristics of approximately 10-fs pulses from a self-mode-locked Ti:sapphire laser were found to exhibit large deviations from the predictions of current theories of mode locking. A simple model that takes into account coherent coupling between the circulating pulse and the gain medium gives results in good agreement with experimental observations.

Periodic pulse evolution in solitary lasers

The periodic variation of femtosecond pulse characteristics within a mode-locked Ti: sapphire laser is investigated. By measurement of the output pulse characteristics at the dispersive and the nondispersive ends of a femtosecond Kerr-lens mode-locked laser cavity, it has been demonstrated that both the laser bandwidth and the pulse duration are functions of position within the laser cavity. A qualitative argument is also presented that predicts near-bandwidth-limited pulses at the cavity extremes, and this prediction is confirmed by experiment.