Abstract-High-energy terahertz pulses from semiconductors pumped beyond the three-photon absorption edge

Gy. Polónyi, B. Monoszlai, G. Gäumann, E. J. Rohwer, G. Andriukaitis, T. Balciunas, A. Pugzlys, A. Baltuska, T. Feurer, J. Hebling, and J. A. Fülöp

A new route to efficient generation of THz pulses with high-energy was demonstrated using semiconductor materials pumped at an infrared wavelength sufficiently long to suppress both two- and three-photon absorption and associated free-carrier absorption at THz frequencies. For pumping beyond the three-photon absorption edge, the THz generation efficiency for optical rectification of femtosecond laser pulses with tilted intensity front in ZnTe was shown to increase 3.5 times, as compared to pumping below the absorption edge. The four-photon absorption coefficient of ZnTe was estimated to be 𝛽4=(4±1)×10−5${\beta }_4=\left(4\pm 1\right)\times {10}^{-5}$ cm5/GW3. THz pulses with 14 μJ energy were generated with as high as 0.7% efficiency in ZnTe pumped at 1.7 µm. It is shown that scaling the THz pulse energy to the mJ level by increasing the pump spot size and pump pulse energy is feasible.

© 2016 Optical Society of America

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Abstract-Highly efficient scalable monolithic semiconductor terahertz pulse source

J. A. Fülöp, Gy. Polónyi, B. Monoszlai, G. Andriukaitis, T. Balciunas, A. Pugzlys, G. Arthur, A. Baltuska, and J. Hebling
https://www.osapublishing.org/optica/abstract.cfm?uri=optica-3-10-1075

Intense pulses at low terahertz (THz) frequencies of 0.1–2 THz are an enabling tool for constructing compact particle accelerators and for strong-field control of matter. Optical rectification in lithium niobate provided sub-mJ THz pulse energies, but it is challenging to increase it further. Semiconductor sources suffered from low efficiency. Here, a semiconductor (ZnTe) THz source is demonstrated, collinearly pumped at an infrared wavelength beyond the three-photon absorption edge and utilizing a contact grating for tilting the pump-pulse front. Suppression of free-carrier absorption at THz frequencies in this way resulted in 0.3% THz generation efficiency, two orders of magnitude higher than reported previously from ZnTe. Scaling the THz energy to the mJ level is possible simply by increasing the pumped area. This unique THz source with excellent focusability, pumped by novel, efficient infrared sources, opens up new perspectives for THz high-field applications.

© 2016 Optical Society of America

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Abstract-GV/m single-cycle terahertz fields from a laser-driven large-size partitioned organic crystal

C. Vicario, B. Monoszlai, and C. P. Hauri

https://journals.aps.org/prl/accepted/c7079Yf5Cf718537276d86f4c4bdf3efaa38d538e

We report on compact and efficient laser-based THz generation in the Terahertz frequency gap (1-10 THz). The radiation is generated by optical rectification of a mid-infrared laser in a large-size, partitioned nonlinear organic crystal assembly. This enables up-scaling of presently field-limited table-top THz sources to GV/m electric and several Tesla magnetic field at millijoule pulse energy. In agreement with simulations the THz beam properties at focus are shown to be not deteriorated by the discontinuity of the emitter surface. The high laser-to-THz energy conversion efficiency exceeds the Manley-Rowe limit and is explained by a cascaded chi^(2) process in the organic crystals accompanied by a significant red shift of the pump spectrum. The scheme provides a compact, table-top THz source for single-cycle transients at field strength equivalent or even higher to linear accelerator and FEL-based THz sources. This opens an avenue towards novel nonlinear THz applications.