|Institution:||University of Rochester|
|Full text PDF:||http://hdl.handle.net/1802/32425|
In this thesis I present experiments in which weexcited classical-limit states of an atom using terahertz pulses.In a classical-limit state, an atom's outer electron is confined toa wave packet that orbits the core along a classical trajectory.Researchers have excited states with classical traits, but wavepackets localized in all three dimensions have proved elusive.Theoretical studies have shown such states can be created usingterahertz pulses. Using these techniques, we created a linear-orbitwave packet (LOWP), that is three-dimensionally localized andorbits along a line on one side of the atom's core. Terahertz pulses are sub-picosecond bursts offar-infrared radiation. Unlike ultrashort optical pulses, theelectric field of terahertz pulses barely completes a single cycle.Our simulations of the atom-pulse interaction show that thiselectric field profile is critical in determining the quality ofthe wave packet. To characterize our terahertz pulses, we inventeddithered-edge sampling which time-resolves the electric field usinga photoconductive receiver and a triggered attenuator. We alsostudied how pulses are distorted after propagating through metallicstructures, and used our findings to design our atomic experiments. We excited wave packets in atomic sodium usinga two-step process. First, we used tunable, nanosecond dye lasersto excite an extreme Stark state. Next, we used a terahertz pumppulse to coherently redistribute population among extreme Starkstates in neighboring manifolds. Interference between the finalstates produces a localized, dynamic LOWP. To analyze the LOWP, weionized it with a stronger terahertz probe pulse, varying thepump-probe delay to map out its motion. Weobserved two strong LOWP signatures. Changing the static electricfield produced small changes (2%) in the orbital period that agreedwith our theoretical predictions. Secondly, because the LOWPscatters off the core, the pump-probe signal depended on thedirection of the kick the LOWP received from the probe pulse. Theseobservations, combined with our detailed simulations that usedsodium parameters and the actual shape of the terahertz pulse, leadus to conclude that we excited a LOWP.