Abstract: Various examples of an optically pumped laser are described. In each example, a laser member formed from active laser material is located in an optical cavity and a source of pumping light is arranged so that pumping light passes into the laser member through a side surface. A deflecting means is provided which ensures that the pumping light makes an initial pass followed by at least one, and preferably at least two, further passes across the laser member. In the further passes, the pumping light has a substantial component long the optical axis. Consequently, a relatively long absorption path for the pumping light is achieved. In one example, the laser member is an Nd:YAG bar (20), the pumping light source is an array (23) of laser diodes, and the deflecting means takes the form of a series of facets (27) formed along a side of the bar (20). In another example, the deflecting means is a diffraction grating.

Abstract: In order to compensate for the thermally induced lens in the active element of an optical stage of a laser, the optical stage is provided with a telescope. The telescope comprises first and second lens arrangements. The first lens arrangement is located so that thermally induced lens is located at one of its focal planes. The position of the second lens arrangement is adjusted so as to compensate for variations in the power of flashlamps which pump the active element. In one embodiment, the laser has an oscillator stage and an amplifier stage. The telescope is placed after the oscillator stage and comprises two convex lenses.