Abstract

Applications for pulsed CO₂ lasers in coherent radar systems generally require that the transmitter laser operates single mode and with a high degree of frequency stability. In pulsed CO₂ lasers discharge effects [1] and a laser induced effect [2] lead to frequency sweeping. For longer pulse operation in particular the laser induced effect is the major source of frequency sweeping. This mechanism shows an inverse 4th power dependence on beam spot size and can, therefore, be minimised by employing cavities which enable a large mode radius to be achieved whilst maintaining good discriminiation against higher order transverse modes. Such a geometry enables large mode volumes to be obtained from short resonators allowing high energy operation from compact structures. Furthermore, since the energy is dispersed over a large area of mirror surface good resistance to damage should ensue.

© 1987 Optical Society of America