Neutral Particle Acceleration By Laser Pulse In Vacuum

When the atom is exposed to strong laser field, the electric field force on the electron may achieve or even exceed the Coulomb force, so that the atoms will be ionized. If we choose proper laser field, the electron may not get enough energy and Rydberg atom produced. The electron in the Rydberg atom stays in high excitation state, it is far from the nuclear, so that when the Rydberg atom is exposed to the inhomogeneous laser field, there will be a force on it and the Rydberg atom will be accelerated. The intensity-dependent force very much resembles the ponderomotive force acting on charged particles.We simulate the motion of the charged particle in the laser field using electromagnetic force method and ponderomotive force method. By comparing the numerical simulation results, we discuss the ponderomotive force. We theoretically analyse the movement of the stimulated neutral atoms in the laser field. We obtained the maximum speed formula of excited neutral atoms in detail, and the speed distribution of the neutral atom located at the laser beam waist according to the speed formula.Besides, we simulate the accelerating process of the neutral atoms with different width of laser waist. The results show that, the atom gets the best acceleration effect in the radial position of half waist. With increase pulse length, the radial maximum speed of excited neutral atoms getting from the light field increases. We use different waist width laser beam to simulate the acceleration process of neutral atoms, and find that the distribution peak of the maximum exit velocity becomes narrow with the laser waist decreasing. Subsequently, we use the maximum velocity formula to calculate the maximum exit velocity of excited neutral atoms by different laser width, and the calculation results and our simulation results are almost the same.This paper can help us better understand the internal mechanism of using the laser to accelerate neutral atoms, and also be able to provide some help on selecting better acceleration condition in experiment.