Stabilising system for laser beam alignment - has temperature-controlled raising and lowering device to compensate for drift due to temperature effects

摘要

The beam position is detected at a receiver matrix (8) at the far end of the optical system. The position detector gives an output proportional to displacement of the beam from its datum point (30) and a comparator-type control circuit (14) connected to the detector provides a variable voltage to a heating coil wound around a vertical aluminium tube (7) fixed to the rear support of the laser tube. A foot in the form of an Invar rod (27), passes through the centre of the aluminium tube and is fixed to its upper end. Increased heating current causes the tube to expand, lowering the rear of the frame and raising the laser beam. If the laser beam is too high, a reduced heating current allows the tube to shorten, raising the support end and lowering the beam to its required level. Vertical movement of the optical bench (1) is detected by a semi-reflecting mirror and second receiver element (35) placed midway along the bench.