Ultrafast spectroscopy is widely used to probe fundamental electronic interactions in semiconductor nanostructures and devices using femtosecond lasers. The dynamics of photoexcited semiconductors can be measured on the timescale of 10 -14 s using ultrafast optical spectroscopy. The electrons and holes interact with each other to form a hot plasma, which then cools by emitting phonons. The main thrust of the programme lies in the area of quantum wells, wires and dots. The development of full colour light sources based on semiconductor lasers is an important goal in the fields of optical displays and communications.
Experiments use time-resolved photoluminescence, optical absorption and reflectance spectroscopy.
Optically-pumped lasers are being studied in order to develop an understanding of excitonic scattering and localisation processes, plasma formation and energy relaxation. Squeezed states of light J F Ryan Quantum states of light, unlike their classical counterparts, cannot be assigned precisely defined values of amplitude and phase. These quantities have zero-point fluctuations, the scale of which is set by the electric field of a single photon, which limit the sensitivity of optical measurements and reduce the efficiency of optical communications. In the former case, nonlinear optical techniques using femtosecond lasers are applied, while in the latter case, high quantum efficiency LED s and lasers are being investigated. New photonic tools are now emerging from this research - quiet lasers, noiseless amplifiers and quantum optical repeaters, and there is strong interest in developing techniques for quantum communications.