Abstract

Progress in ultrafast spectroscopy technology has enabled us to generate and to directly observe the coherent oscillation of phonon modes. In semiconductors, carriers can be excited by ultrashort laser pulses in a spatial area much larger than one unit cell and the excited carrier populations (with wave vector q≅0) are coupled to the corresponding optical phonon modes. Some of these optical phonon modes can behave like classical oscillators and have non-zero time- dependent displacements. The corresponding modulation of the material dielectric constant could then be observed by changes in the intensities of transmitted or reflected probe light pulses [1,2].

© 1999 Optical Society of America