LAUSR

The chirp characteristics and the effect of chirp on the beam quality of laser pulses propagating from the ground through the atmosphere to the space orbit are studied. The analytical expressions of the additional chirp caused by group-velocity dispersion (GVD) and self-focusing effects in the atmosphere are derived, respectively. It is shown that the behavior of the additional chirp caused by GVD effect is quite different from that caused by self-focusing effect. On the other hand, it is found that there exists a minimum of pulse width on the target when a certain negative initial chirp arrives. In particular, it is demonstrated that the beam quality on the target can be optimized (i.e., the target intensity can be improved and the temporal pulse splitting on the target can be avoided) by the preliminary chirp method.