  High energy photons can be generated via inverse Compton scattering (ICS) in
the collision between energetic electrons and intense laser pulse. The
development of laser plasma accelerators promises compact and all-optical
gamma-ray sources by colliding the electrons from laser wakefield accelerators
to its high-power driving pulse reflected by a plasma mirror. However, the law
of optical focusing hinders realization of both high photon yield and
monochromatic spectrum in this scenario. We propose an azimuthal
spatial-temporal convertor that decouples the focal field strength from laser
spot size using helical parabolic geometry. It decomposes the driving laser
beam into a pulse train of almost identical divergence angle and focal depth,
creating synchronized ICS in the optimized linear regime. The scheme resolves
the dilemma between high efficiency and narrow energy spread, facilitating the
generation of monochromatic gamma-ray using high power lasers beyond
relativistic field strengths.
