FREQUENCY STABILISED LASER AND CONTROL SYSTEM THEREFOR

摘要

In a multiple frequency laser the output frequencies are stabilised by a control system including a heater (18) for heating the laser cavity and thus varying its length, and a heater control circuit (20) which includes means for monitoring the intensities of the modes (P1, D1, P2, D2) in the cavity. Adjacent modes of the laser are orthogonally polarised and the control system further includes means for maintaining constant the ratio of the sums of the intensities of the modes in the two orthogonal polarisation planes in order to stabilise the laser frequencies. In the described embodiment the laser is a dual frequency laser having two orthogonally polarised modes and the control system maintains the ratio of the intensities of the two modes constant at a pre-determined value.