Laser diagnostics using light intensity measurements for continuously emitting active media

The intensity of light extracted from an optical cavity is a sensitive function of the peak absorption coefficient, k0, and can be used to survey the evolution of k0 when the parameters of the active medium are changed during the process of laser development. This provides a means for identifying the spectral lines which may be suitable for lasing transitions and an indication of how to optimize k0 when it is still below the laser threshold. The theoretical dependence of the measured intensity on k0 is derived for continuously emitting media, arbitrary optically stable cavity configurations, and symmetric or asymmetric line profiles. The calculations show that the light intensity at an axial point is produced by those light sources which are confined in certain emission volumes within the active medium determined by the diaphragming conditions of the measuring system. Two basic measurement modes were identified according to whether the emission volumes are controlled (a) by the mirror apertures or (b) by an adjustable external diaphragm. The latter measuring mode is independent of all cavity geometrical parameters, and the experimental test which confirmed this conclusion indicates that the absolute error in the measurement of k0d, where d is the active medium length, is 0.015 for small absorptions and for cavity losses lower than 12 percent per round trip