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We propose an operation switchable ring-cavity erbium-doped fiber laser (EDFL) via intra-cavity polarization control. By using a semiconductor saturable absorber mirror in the EDFL cavity, stable Q-switching, Q-switched mode-locking, continuous-wave mode-locking, pulse splitting, and harmonic mode-locking pulses can be manipulated simply by detuning a polarization controller while keeping the pump power at the same level. All EDFL operation states can be obtained under the polarization angles detuning within 180 degrees. Continuous-wave mode-locking of EDFL with 800-fs pulsewidth repeated at 4 MHz has been obtained, for which the output pulse energy is 0.5 nJ and the peak power is 625 W. Interaction between solitons and the accompanied non-soliton component will lead to either pulse splitting or 5th-order harmonic mode-locking at repetition rate of 20 MHz.

We experimentally show, for the first time to our knowledge, that a diode-pumped Nd:YVO 4 laser can operate with multipass transverse (MPT) modes that self-reproduce after several round trips in a plano-concave cavity that has fractionally degenerate resonator configurations when the pump beam waist is sufficiently smaller than that of the fundamental cavity mode. The MPT mode is found to exhibit multiple beam waists located at different positions and to experience a lower pumping threshold than the single-pass transverse mode. With off-axis pumping, the N-pass transverse mode forms a symmetric pattern for even N and an asymmetric pattern for odd N. This result can be explained as being due to the introduction of MPT modes but not to superposition of the standard cavity modes.

We report the observation of harmonic mode locking and multiple pulse operations in a soft-aperture Kerr-lens mode-locked Ti:sapphire laser by varying the total intra-cavity dispersion. Second, third, and fourth order harmonic mode locking as well as multiple pulsing with interpulse separation ranging from femtosecond to nanosecond are observed. The laser is characterized in these regimes in terms of wavelength, bandwidth, pulsewidth, average and peak powers as functions of group velocity dispersion. By introducing a loss difference term into gain dynamic analysis, we conclude that gain depletion and recovery mechanisms are responsible for the underlying physics of current observations.