  To measure and control the electron motion in atoms and molecules by the
strong laser field on the attosecond time scale is one of the research
frontiers of atomic and molecular photophysics. It involves many new phenomena
and processes and raises a series of questions of concepts, theories and
methods. Recent studies show that the Coulomb potential can cause the
ionization time lag (about 100 attoseconds) between instants of the field
maximum and the ionization-rate maximum. This lag can be understood as the
response time of the electronic wave function to the strong-field-induced
ionization event. It has a profound influence on the subsequent ultrafast
dynamics of the ionized electron and can significantly change the
time-frequency properties of electron trajectory (an important theoretical tool
for attosecond measurement). Here, the research progress of response time and
its implications on attosecond measurement are briefly introduced.
