Abstract: An etalon for use in lasers, particularly CW dye lasers, comprises a pair of plates, 10,11 respectively mounted at the ends of a tube 12 with the distal faces 10a, 11a of the plates parallel and the chamber 13 formed within the tube 12 between plates 10,11 is substantially completely filled with a fluid 20 whose refractive index matches that of the plates 10,11 and means 25 are provided for causing extension and contraction of the axial spacing of the plates 10,11. In one embodiment the tube 12 is made of piezoelectric material and the means 25 provides an electrical drive signal to the piezoelectric material. In another embodiment the tube 12 has piezoelectric portions and other portions made of a rigid material. In a further embodiment the tube has portions made of a rigid material which are separated by an elastomer 39 and the means 25 includes a pump 26 which is in fluid communication with the chamber 13.

Abstract: A laser of the kind in which the lasing medium is a free flowing dye stream incorporates a means of tuning the output wave length of the laser, this means being in the form of a wedged birefringent plate which is driven in a linear mode by a linear translator so that the thickness of the birefringent plate traversed by the intracavity beam of laser light may be varied.