  This paper theoretically analyzes the behavior of an atom driven by a strong
electro-magnetic field. Moreover, besides traditional quantum mechanics method,
we also investigate semiclassical approaches to this problem. We first
performed strong field approximation for system of an atom driven by a strong
electromagnetic field in velocity gauge. Our simulation result is consistent
with theories and close to experiments except some reasonable difference caused
by different parameters and omitted bound and final states in the transition
amplitude. Next, a new semiclassical approach is used to solve Volkov wave
function. We prove that semiclassical approximation works well in predicting
the particle evolution in quantum world, especially for system in a strong
electromagnetic field with low frequency. Finally, we also briefly illustrated
how to use semiclassical approximation to get the same results as strong field
approximation and also partly tested the viability of the semiclassical
approach to Teller Potential. This part needs future work to accomplish. But
still, semiclassical approximation provides a potentially new method to solve
complicated system, which might be more effective than traditional quantum
mechanics recipe.
