Low divergence laser apparatus

A laser device including a low divergence laser oscillator of the kind wherein an intra-cavity beam is propagated within an optical resonator along a resonator axis and within an oscillator portion of the volume of an active medium, and wherein a part of said intra-cavity beam intensity is coupled out of the oscillator by a first outcoupling means as an extra-cavity beam, propagating along an optical path external to said optical resonator, characterized in that there is provided:

• an introducing means positioned within said optical resonator and in said optical path for directing said extra-cavity beam into said active medium as a reintroduced beam, so that a closed loop is formed by said optical path and said resonator axis,
• a second outcoupling means within said optical resonator for extracting out of said laser device said reintroduced beam after amplification in said active medium as an output beam, and
• a beam expanding means positioned within said closed loop for expanding the beam therein such that the cross-sectional area of said reintroduced beam as it enters said active medium is substantially greater than that of said oscillator portion;
• wherein said introducing means and said second out-coupling means include a polarizing element and
• an arrangement is such that said intra-cavity beam and said reintroduced beam propagating along said active medium are linearly polarized at planes substantially orthogonal to each other.