  Photon-induced near-field electron microscopy (PINEM) is a currently
developing spectral approach that characterizes quantum electron-light
interactions in electron energy gain/loss spectrum, with symmetrically
discretized gains or losses of light quanta ($\hbar \omega$), coupled with a
laser induced optical near-field. In this letter, we have demonstrated that
Linear Particle Accelerator (LPA) and anomalous PINEM (APINEM) can analytically
emerge from PINEM-kind interaction in a strong coupling regime, because of
quantum interference of spectral photon sidebands overlap. Furthermore, we also
found that the quantum interference in point-particle regime with
pre-interaction drift can produce interesting optical spectral focusing and a
periodically bunching of energy/momentum distribution that enable us to improve
the spectral resolution of electron microscopy, imaging and spectroscopy. These
observation of LPA and APINEM in strong laser physics can be of great interests
for both theoretical and experimental communities, such as ultrafast electron
microscopes, attosecond science and laser-driven accelerators.
