Mittleman This award provides partial support for the development of an ultrabroad band terahertz emission spectrometer for materials research at Rice University. Recently, there has been a great deal of activity in the development of new spectroscopic methods based in the far infrared, or terahertz, range of the electromagnetic spectrum. These have been driven by the importance of the numerous physical phenomena which are active in this spectral range, and by the relative difficulty in generating and detecting terahertz radiation using conventional means. One of the more interesting of these systems is known as terahertz time-domain spectrocopy (THz-TDS). This technique relies on femtosecond laser technology, in combination with conventional electronics, to generate sub-picosecond pulses of terahertz radiation, with very high signal-to-noise ratios over extremely broad bandwidths. This unique system has been used in recent years as a novel spectroscopic tool in studies of many different materials. Very recent developments in the coherent detection scheme have led to dramatic enhancements in the accessible bandwidths, by as much as an order of magnitude.
This award will exploit these new techiques, in order to gain a better understanding of the ultrafast charge carrier dynamics in a broad range of electronic materials. In particular, this advance is of particular importance in the area of terahertz emission spectroscopy. Here, the THz radiation emitted by a sample which has been excited by an ultrafast laser pulse can be used to monitor the acceleration of charge carriers. By accurately measuring the emitted electric field ETHz(t), valuable information can be inferred about the ballistic motion of charge carriers, carrier screening and space charge effects, and displacement polarization dynamics. This emission spectroscopy has been increasingly valuable in recnet years in studies of many different material systems. In combination with pump-probe techniques, it can be used to observe charge carrier dynamics on a 10 femtosecond time scale. However, the information gleaned in such experiments is incomplete if the emitted radiation bandwidth extends substantially beyond the acceptance bandwidth of the detectors used in the study. The recent advances involving the extension of this acceptance bandwidth will greatly enhance the value of this experimental technique. This exciting new capability will be used to study the ultrafast dynamical processes involved in carrier transport in a number of material systems, including bulk semiconductors, heterostructures, and superconducting systems.
This development effort will be directed towards the construction of a versatile ultrabroadband THz emission spectrometer, for use in materials research. It will be configured to perform both linear and non-linear THz emission experiments, with the broadest possible detection bandwidth. Three initial experiments are proposed; these should provide valuable new information about the fundamental transport of polarization dynamics in several important classes of materials. Additionally, the unique capabilities of this spectrometer will provide the opportunity for interaction with several researchers affiliated with the Center for Nanoscale Science and Technology, a new materials research effort at Rice University. Consequently, this development project is expected to have a broad impact, not only on the PI's research program, but also through interactions with members of the Physics, Chemistry, and Electrical and Computer Engineering Departments. %%% ***
