Light-Force Technique for Measuring Polarizabilities

This thesis presents a new technique for measuring polarizabilities which uses a pulsed electromagnetic standing wave to change the velocity distribution of an atomic beam. The technique was evaluated by measuring the polarizability of rubidium, which has been measured using static fields. It is surprising that the polarizability, the lowest order electric moment of an atom, has not been measured for the majority of elements in the periodic table. The technique presented here was developed specifically to address the difficulties in measuring the polarizabilities of refractory elements. An intense, non-resonant, pulsed laser is reflected from a mirror to form a standing wave. The conservative dipole force on an atom is proportional to the polarizability of the atom, and is proportional to the gradient of the intensity of the standing wave at the position of the atom. The atoms are detected by measuring the absorption of a near -resonant cw laser which is 0.6 cm downstream from the standing wave. The standing wave gives the atoms velocity kicks which Doppler-shift the resonance frequencies of the atoms, resulting in an increase or reduction in the absorption of the probe laser. The polarizability is deduced by measuring the change in absorption as a function of | v_{xi}, the mean initial velocity of the atomic beam along the standing-wave laser axis. The atomic beam is produced using two-stage laser ablation, a technique developed for this work to produce a pulsed atomic beam with a high peak number density. For the measurement of atomic polarizabilities, two-stage laser ablation is used to produce a beam of particles which is intrinsically well collimated. We also demonstrate that two-stage laser ablation can be used to produce a focused beam of neutral particles. Using a Nd:YAG laser at lambda_ {sw} = 1.064 mu for the standing wave, the polarizability of rubidium is measured to be alpha(omega_ {sw}) = 114 +/- 9 A^3(sigma). A semiempirical formula is used to determine a static polarizability of alpha_{dc} = 52 A^3, within 10% of previously published results.