15 February 2018 Frequency-shifted sources for terahertz-driven linear electron acceleration
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The generation of THz-frequency radiation via nonlinear parametric frequency down-conversion has long been driven by the spectroscopy and imaging communities. As a result, little efforts have been undertaken toward the generation of high energy THz-frequency pulses. THz-frequency radiation has however recently been identified has a promising driver for strong-field physics and an emerging generation of compact particle accelerators. These accelerators require THzfrequency pulses with energies in the multi-millijoule range therefore demanding orders of magnitude improvements from the current state-of-the-art.

Much can be gained by improving the intrinsically low efficiency of the down-conversion process while still resorting to existing state-of-the-art lasers. However, the fundamental Manley-Rowe limit caps the efficiency of parametric downconversion from 1-μm wavelength lasers to sub-THz frequency to the sub-percent range.

We present methods that promise boosting the THz radiation yield obtained via parametric down-conversion beyond the Manley-Rowe limit. Our method relies on cascaded nonlinear three-wave mixing between two spectrally neighboring laser pulses in periodically poled Lithium Niobate. Owing to favorable phase-matching, the down-conversion process avalanches, resulting in spectral broadening in the optical domain. This allows in-situ coherent multiplexing of multiple parametric down-conversion stages within a single device and boosting the efficiency of the process beyond the ManleyRowe limit. We experimentally demonstrated the concept using either broadband, spectrally chirped optical pulses from a Joule-class laser or using two narrowband lasers with neighboring wavelengths. Experimental results are backed by numerical simulations that predict conversion efficiencies from 1 μm to sub-THz radiation in the multi-percent range.
Conference Presentation
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M. Hemmer, M. Hemmer, G. Cirmi, G. Cirmi, K. Ravi, K. Ravi, F. Ahr, F. Ahr, L. Zapata, L. Zapata, A.-L. Calendron, A.-L. Calendron, H. Çankaya, H. Çankaya, S. W. Jolly, S. W. Jolly, V. Leroux, V. Leroux, T. Eichner, T. Eichner, H. Ishizuki, H. Ishizuki, T. Taira, T. Taira, N. Matlis, N. Matlis, A. R. Maier, A. R. Maier, F. X. Kärtner, F. X. Kärtner, "Frequency-shifted sources for terahertz-driven linear electron acceleration", Proc. SPIE 10516, Nonlinear Frequency Generation and Conversion: Materials and Devices XVII, 105160F (15 February 2018); doi: 10.1117/12.2295357; https://doi.org/10.1117/12.2295357

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