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62THz-I-10
On the way to generation and application of extremely high field THz pulses
J. Hebling1'2'3, T. Gyorgy1, Nugraha P. S.23, L. Palfalvi1, A. Andras Fulop2'3, Krizsan G.13, L. Tokodi1, Z. Tibai1, G. Almasi13
institute of Physics, University of Pecs, Ifjusag u. 6. Pecs 7624, Hungary 2MTA-PTE High-Field Terahertz Research Group, Ifjusag u. 6, Pecs 7624, Hungar 3Szentagothai Research Centre, University of Pecs, Ifjusag u. 20, Pecs 7624, Hungary
Acceleration of electrons [1] and protons [2], and generation of single-cycle attosecond pulses [3] are promising applications of very intense terahertz (THz) pulses. One of the most effective ways to generate high energy near single-cycle THz pulses is the optical rectification of tilted-pulse-front (TPF) pump pulses in LiNbO3 (LN) crystal [4]. Using this technique, the energy of the generated THz pulses was increased by six orders of magnitude reaching the mJ level in the last decade [5]. However, the energy scalability is limited by the imaging errors and the large angular dispersion connected to the needed large tilt angle. Furthermore, the prism shape of the LN has significant influence on the quality of the generated beam shape. To reduce the effect of angular dispersion, a modified version of the TPF THz generation was demonstrated by replacing the optical grating to a stair-step echelon [6]. A high THz generation efficiency was achieved, but this echelon setup still requires a prism-shaped nonlinear crystal with the same wedge angle as in the conventional setup. Recently, we proposed [7] and demonstrated [8] a hybrid-type setup (Fig. 1), which is a combination of the conventional scheme, containing diffraction optics and imaging, and a nonlinear material with an echelon profile created on its entrance surface (nonlinear echelon slab, NLES). Contrary to all the LN setups used so far, a plane parallel nonlinear crystal can be used. Because of the plan-parallel structure and the reduced tilt angle, the beam quality is perfect, contrary to the beam generated by conventional TPF setup (see Fig. 2a,b).
Fig. 1. Scheme of the proposed and demonstrated nonlinear echelon slab (NLES) hybrid THz source.
To overcome the drawbacks of imaging errors, we proposed an imaging-free NLES setup [9]. In this case not the plane parallel NLES results uniform THz beam shapes, instead one with a small wedge angle (8.6°). The efficiency exceeds that of the conventional setup and plane parallel NLES (Fig. 2c).
Time (pt) Crystal length (mm)
Fig. 2. Calculated THz pulse waveforms at different position across the THz beam for a LN-based plan parallel NLES (a) and a prism (b). Optical to THz generation efficiency of the conventional setup, the plane parallel NLES
(with imaging) and the imaging-free NLES setup. (c).
Using NLES setups, the generated THz pulse energy is perfectly scalable to 10s of mJ level
simply by increasing the pump beam diameter, in contrast to the conventional, prism-based setup.
According to our calculations generation of multicycle THz pulses is also possible with high
efficiency by NLES if the pump pulse is intensity-modulated.
Funding: European Union, co-financed by the European Social Fund Grant (EFOP-3.6.1-
2016-00004).
References
[1] A. Fallahi, M. Fakhari, A. Yahaghi, M. Arrieta, and F. X. Kartner, "Short electron bunch generation using single-cycle ultrafast electron guns," Physical Review Accelerators and Beams 19, 081302 (2016).
[2] L. Palfalvi, J. A. Fulop, G. Toth, and J. Hebling, "Evanescent-wave proton postaccelerator driven by intense THz pulse," Physical Review Special Topics - Accelerators and Beams 17, 031301 (2014).
[3] Gy. Toth, Z. Tibai, A. Sharma, J. A. Fulop, and J. Hebling, "Single-cycle attosecond pulse by Thomson backscattering of terahertz pulses," J. Opt. Soc. Am. B 35, A103-A109 (2018).
[4] J. Hebling, G. Almasi, I. Z. Kozma, and J. Kuhl, "Velocity matching by pulse front tilting for large-area THz-pulse generation," Opt. Express 10, 1161-1166 (2002).
[5] J. A. Fulop, Z. Ollmann, C. Lombosi, C. Skrobol, S. Klingebiel, L. Palfalvi, F. Krausz, S. Karsch, and J. Hebling, "Efficient generation of THz pulses with 0.4 mJ energy".
[6] B. K. Ofori-Okai, P. Sivarajah, W. R. Huang, and K. A. Nelson, "THz generation using a reflective stair-step echelon," Opt. Express 24, 5057-5068 (2016).
[7] L. Palfalvi, Gy. Toth, L. Tokodi, Zs. Marton, J. A. Fulop, G. Almasi, and J. Hebling, "Numerical investigation of a scalable setup for efficient terahertz generation using a segmented tilted-pulse-front excitation," Opt. Express 25, 29560-29573 (2017).
[8] P. S. Nugraha, G. Krizsan, Cs. Lombosi, L. Palfalvi, Gy. Toth, G. Almasi, J. A. Fulop, and J. Hebling, "Demonstration of a Tilted-Pulse-Front Pumped Plane-Parallel Slab Terahertz Source," accepted in Opt. Lett.
[9] Gy. Toth, L. Palfalvi, J. A. Fulop, G. Krizsan, N. H. Matlis, G. Almasi, and J. Hebling, "Numerical investigation of imaging-free terahertz generation setup using segmented tilted-pulse-front excitation," accepted in Opt. Express.
