  Quantum radiated power emitted by an Unruh-DeWitt (UD) detector in linear
oscillatory motion in (3+1)D Minkowski space, with the internal harmonic
oscillator minimally coupled to a massless scalar field, is obtained
non-perturbatively by numerical method. The signal of the Unruh-like effect
experienced by the detector is found to be pronounced in quantum radiation in
the highly non-equilibrium regime with high averaged acceleration and short
oscillatory cycle, and the signal would be greatly suppressed by quantum
interference when the averaged proper acceleration is sufficiently low. An
observer at a fixed angle would see periods of negative radiated power in each
cycle of motion, while the averaged radiated power over a cycle is always
positive as guaranteed by the quantum inequalities. Coherent high harmonic
generation and down conversion are identified in the detector's quantum
radiation. Due to the overwhelming largeness of the vacuum correlators of the
free field, the asymptotic reduced state of the harmonics of the radiation
field is approximately a direct product of the squeezed thermal states.
