Terahertz-driven AC Stark effect in quantum-confined magnetoexcitons

The states of a quantum system can be dressed by strong interaction with intense oscillating fields. This ``AC Stark effect'' has been widely studied in atoms driven by intense laser radiation. Quantum-confined semiconductor systems, with their large intraband oscillator strengths, are promising for observing large AC Stark shifts and anticrossings of dressed states. A quartz-tungsten halogen lamp and multichannel spectrometer are used to measure the interband absorption spectrum of excitons confined to undoped GaAs/AlGaAs quantum wells in magnetic fields from 0-12 T. Intense THz electric fields from the UCSB Free-Electron Laser shift the excitonic absorption energies by several meV, possibly due to an AC Stark effect. Supported by ONR, QUEST (a NSF Science and Technology Center), and JSTC.