Methods, apparatus, and systems comprising a fiber-coupled laser and time-varying beam characteristics. A laser may generate an optical beam that is launched into one or more lengths of fiber, at least one of which comprises a confinement region that is optically coupled to an output. A perturbation device may modulate, through action upon the one or more lengths of fiber, a beam characteristic over a time period during which the laser is energized. A controller may cause the perturbation device to act upon the one or more lengths of fiber to impart a time-averaged beam characteristic and/or to induce a continuous variation in one or more beam characteristics during system use. A process monitor may sense a metric external to the optical system, and a feedback signal from the process monitor may be coupled into the controller. Dynamic beam characteristics may be modulated based on the feedback signal.