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Abstract

A pulsed laser for machining, has a mode switch, e.g. Q-switch device (15, 30, 40), in a resonant optical cavity (20) capable of supporting a given lasing mode, e.g. a transverse mode of oscillation when lasing action is started, arranged to induce, e.g. temporarily, a localized change, e.g. loss, in the cavity. The latter alters the given lasing mode, e.g. causes the oscillation to hop to a higher transverse mode temporarily, which on its hand may be extinguished by an aperture limiting diaphragm (5) or equivalent and subsequently reduce the induced loss temporarily, to return the oscillation to the given transverse mode and output the laser pulse. A modulator can be used for inducing the temporary loss for a first transverse lasing mode and extinguishing the higher transverse mode with a diaphragm. The induced loss can be over a localized area much smaller than the dimensions of a beam of the laser, so that a miniaturized modulator can be used. In this way pulsed operation may be achieved. Alternatively, a steady switch between modes may be achieved.

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