  Two types of synchronization, Achronal Synchronization and Isochronous
synchronization are investigated numerically when unidirectionally coupled
laser systems are considered both on fast and slow dynamics by studying the
correlation function. Although the synchronization behaviors are found to be
separated on relatively fast dynamics of chaotic fluctuations while blended
together on slow dynamics of dropout events, their main features revealed are
in a good agreement, which most probably suggests that the observation based on
detections on slow dynamics is of importance when it is the only choice as
detection on fast dynamics is usually extremely hard to be done.
