  Coherent diffractive imaging (CDI) has been widely applied in the physical
and biological sciences using synchrotron radiation, XFELs, high harmonic
generation, electrons and optical lasers. One of CDI's important applications
is to probe dynamic phenomena with high spatio-temporal resolution. Here, we
report the development of a general in situ CDI method for real-time imaging of
dynamic processes in solution. By introducing a time-invariant overlapping
region as a real-space constraint, we show that in situ CDI can simultaneously
reconstruct a time series of the complex exit wave of dynamic processes with
robust and fast convergence. We validate this method using numerical
simulations with coherent X-rays and performing experiments on a materials
science and a biological specimen in solution with an optical laser. Our
numerical simulations further indicate that in situ CDI can potentially reduce
the radiation dose by more than an order of magnitude relative to conventional
CDI. As coherent X-rays are under rapid development worldwide, we expect in
situ CDI could be applied to probe dynamic phenomena ranging from
electrochemistry, structural phase transitions, charge transfer, transport,
crystal nucleation, melting and fluid dynamics to biological imaging.
