Abstract

We have investigated mechanical effects in the interaction of short coherent laser pulses with a thermal atomic cesium beam. In our preliminary experiment, the Cs-beam is transversely illuminated by resonant 30 ps pulses from a modelocked laser (pulse period 12.5 ns). The laser pulse is reflected back into itself and interacts again after 1 ns with the atoms, but this time propagating in the opposite direction In the case of using ideal π-pulses, the first pulse transfers the atoms from the ground state to the excited state and the reflected pulse returns the population to the ground state by stimulated emission of a photon. Thus, the atom has acquired a total momentum of 2 ħk in the direction of the primary pulse. Due to the transverse Gaussian beam profile of the laser, the pulse areas are position dependent, resulting in a decrease of the total momentum transfer compared to the ideal π-pulse case. We have been able to demonstrate a total momentum transfer of 137 ħk for the most probable velocity (v=227 m/s) in the thermal atomic Cs-beam [1]. This is an increase of momentum transfer by a factor of 2.5 compared to the single pass deflection where the reflected pulse is blocked and which is caused by spontaneous light force. The experiment was simulated by using numerical solutions of the generalized optical Bloch equations which show good agreement with the experimental data.

© 1996 IEEE