Abstract
Brightness defines a light source’s ability to nonlinearly interact with matter by driving it out of an equilibrium state. At terahertz (THz) frequencies, beam quality and brightness are peculiar hurdles for several reasons. First, the THz generation efficiency and the resulting pulse energy are low. Second, high brightness is by nature harder to achieve for THz than it is for radiation at shorter wavelengths. So far, nearly mJ [1] of THz radiation has been demonstrated, but the peak THz intensity has been limited to 0.8 GV/m [2]. In this work, we followed a focusing optimization scheme to dramatically confine a low frequency THz pulse (< 5 THz) in space and time at its physical limits to the least possible 3-dimensional light bullet volume of λ3. Our approach depends on finding the optimum settings of pump wavefront curvature and post-generation divergence. This is combined with fast expansion of the THz beam and compromising it over the wide bandwidth of our pulse. We used small aperture organic crystals (OH1 and DSTMS with pulse energy < 100 μJ) to reach fields of 8.3 GV/m, 27.7 T, and intensity of 110 PW/m2 [3]. Such intensities allowed us to induce measurable nonlinearity in dry air with a sub-5 THz pulse [4]. The presented results are foreseen to have a great impact on nonlinear terahertz applications in different science disciplines.
© 2015 IEEE
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