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Abstract

A method of stabilising a laser in order to maintain the laser in SLM operation is disclosed. The laser comprises a resonator cavity comprising an output coupler 2, a laser rod 1 and rear mirror 3. A first beam reflected by an intra-cavity etalon 4 is reflected by a polariser 8 and passes through a quarter-wave plate 13 to a polarisation beam splitter 10. The first beam is detected by a first detector D.sub.x. A portion of a second beam transmitted by the intra-cavity etalon 4 is also reflected by the polariser 8 and similarly passes through the quarter-wave plate 13 to the polarisation beam splitter 10. The second beam is detected by a second detector D.sub.y A difference between the intensity of the two beams detected by the first and second detectors D.sub.x, D.sub.y is determined. The difference signal is fedback to a piezo-electric transducer 9. The piezo-electric transducer 9 is coupled to the rear mirror 3 of the laser and varies the optical length of the resonator cavity in response to the difference signal.

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First Claim