Power Tunable High and Narrowband THz source for THz Pump X-Ray Probe Experiments

Most time resolved studies of processes in materials to date have made use of readily available visible and near-visible pump sources to trigger the events and, thus were able to study only a small subset of phenomena. Recently, investigations of the dynamics stimulated by THz pulses have led to advances like the selective control of an insulator-metal transition, discovery of light induced superconductivity and observation of coherent nonlinear photonic effects that can be used for ultrafast control of materials. Excitations of complex condensed matter driven by THz pulses exhibit interesting dynamics that can also be used in a new generation of electronics. For these experiments it is critical to obtain pump pulses in the THz frequency range (0.3 to 10 THz) that are tunable with a bandwidth on the order of 1% and energy per pulse of ~ 1mJ. Building on our recent successful experiment we propose a three stage THz source scheme. Two of the stages have already been demonstrated separately. In the first stage the beam is modulated in energy by passing through a passive wakefield device. The energy modulation is then converted into a density modulation by means of a chicane. In the third stage, the bunched beam produces a narrowband high power pulse of terahertz radiation by going through a power extractor. The beam based source provides sufficient power and allows for a wide tuning range. Prior to this Phase I proposal we had separately demonstrated two key stages of the proposed three stage THz source. In Phase I we designed, fabricated and tested the third stage separately. A narrowband THz signal was obtained. We designed full scale THz sources in two frequency ranges for experiments at the Brookhaven National Laboratory and Argonne National Laboratory. In Phase II, we plan first to use the ATF facility to demonstrate a full scale THz source and study its spectral purity and bandwidth, power levels, frequency tuning methods and range, and finally the free space matching and radiation patterns. The ultimate objective of the Phase II project is to develop and demonstrate an ultrahigh energy (~ 1 mJ) narrow band tunable THz source. The experience gained during the project will culminate in the design of a standalone THz source based on a compact, few MeV (medical /cargo inspection) accelerator. Commercial Applications and Other Benefits: A tunable, powerful, narrowband THz source will allow scientists to selectively excite and study new dynamic phenomena at light sources. Besides applications for basic science, these sources can find a variety of applications in communications, non-destructive evaluation, radar systems and medical diagnostics.