ATMOSPHERIC THERMAL LENSING IN LASER RESONATORS

Atmospheric absorption degrades laser performance both by absorbing la ser energy within the laser resonator, which increases the loss, and b y inducing a thermal lens in the atmosphere. Atmospheric thermal lensi ng can be quite severe, even when the absorption coefficient is quite modest, A model is developed which describes atmospheric thermal lensi ng; time constants, which are associated with the establishment and de cay of the atmospheric thermal lens, are determined; experiments are p erformed using an injection seeded Ti:Al2O3 laser tuned to the H2O abs orption lines near 0.815 mu m to validate the model; dependence of the atmospheric thermal lens on the laser energy and absorption coefficie nt were measured and found to agree with the model, In addition, the d ecay of the atmospheric thermal lens with time was measured and also f ound to agree with the model predictions.