Toward a practical light source for two-photon bioimaging, we have generated kilowatt peak power of 0.77 mum wavelength and 5 ps optical pulse via second-harmonic generation of the amplified output from a gain-switched 1.55 mum semiconductor laser. This compact scheme and stable optical-pulse-source has been successfully used for the two-photon fluorescence bioimaging of actin filaments in PtK2 cells.