Generation of Tunable THz Pulses

Many phenomena in materials science, physics, chemistry, biology and medicine involve fundamental processes with a spectral signature in the THz range [20]. However, for many years, these processes have been little studied due to the lack of high quality THz sources. Fortunately, the recent developments in THz technology have filled this so-called THz gap [28]. With the emergence of reliable THz sources, the need for arbitrarily shaped THz pulses dedicated to specific applications like communications, signal processing, spectroscopy or coherent/optimal control is more and more felt. Concerning coherent control, selective excitations in the THz spectral region of phonon modes in molecular crystal [41], charge oscillations in semiconductor heterostructures [5, 26] or phonon-polaritons in ferroelectric crystal [9, 40] have already been achieved by means of temporally shaped near-infrared laser pulses. From this point of view, the possibilities of control would be increased if one makes it possible to excite directly the system with shaped THz pulses [27]. To this end, several methods have been developed to extend the generation of arbitrary pulse shapes from the visible and mid-infrared spectral region up to the THz range [1, 8, 10, 16–19, 21, 30, 31, 43]. All are based on the generation of THz pulses by excitation of different types of emitters with spatially and/or temporally shaped optical pulses.