Abstract-Numerical investigation of imaging-free terahertz generation setup using segmented tilted-pulse-front excitation

György Tóth, László Pálfalvi, József A. Fülöp, Gergő Krizsán, Nicholas H. Matlis, Gábor Almási, and János Hebling

Fig. 1 The setup of the investigated hybrid NLES THz source. The dark blue lines represent the pump pulse front at different moments. After diffraction of the pump beam on the transmission grating (TG), it propagates horizontally. Consequently, the phase-fronts are vertical. All γ is measured from a vertical line.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-5-7762

Recently a hybrid-type terahertz (THz) pulse source was proposed for high energy terahertz pulse generation. It is the combination of the conventional tilted-pulse-front setup and a nonlinear crystal with a transmission stair-step echelon of period in the hundred-micrometer range etched into the front face. The tilt angle introduced by the conventional tilted-pulse-front setup (pre-tilt) was chosen to be equal to the tilt-angle needed inside the nonlinear crystal (62° for lithium niobate (LN)) in order to fulfill velocity-matching. In this case, plane-parallel nonlinear optical crystals can be used. The possibility of using a plane-parallel nonlinear optical crystal for producing good-quality, symmetric THz beams was considered the most important advantage of this setup. In the present paper, a thorough numerical investigation of a modified version of that setup is presented. In the new version, the tilted pulse-front is created by a transmission grating without any imaging optics, and a wedged nonlinear optical crystal with a small wedge angle is supposed. According to a 1D numerical code, significantly higher THz generation efficiency can be achieved with a transmission stair-step echelon-faced nonlinear crystal having a 5 – 15-degree wedge angle than with a plane-parallel one or with the conventional tilted-pulse-front setup. Because of the spatially-dependent group-delay dispersion introduced by the transmission grating, a small wedge in the nonlinear crystal improves the spatial homogeneity of the THz-generation process, resulting in higher efficiencies and better beam profiles. At 100 K temperature, and by using 800 nm pump pulses with 20 mJ pulse energy, 100 fs pulse length and 8 mm beam spot radius, approximately 4.5% conversion efficiency and close to 1 mJ terahertz pulse energy can be reached with the newly-proposed setup.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Demonstration of a Tilted-Pulse-Front Pumped Plane-Parallel Slab Terahertz Source

Priyo Syamsul Nugraha, Gergő Krizsán, Csaba Lombosi, László Pálfalvi, György Tóth, GÁbor Almási, József András Fülöp, János Hebling

https://arxiv.org/abs/1808.06122

A new type of tilted-pulse-front pumped terahertz (THz) source has been demonstrated, which is based on a lithium niobate plane-parallel slab with an echelon structure on its input surface. Single-cycle pulses of 1 microjoule energy and 0.30 THz central frequency have been generated with 0.05% efficiency from such a source. One order-of-magnitude increase in efficiency is expected by pumping a cryogenically cooled echelon of increased size and thickness with a Ti:sapphire laser. The use of a plane-parallel nonlinear optical crystal slab enables straightforward scaling to high THz pulse energies and to produce a symmetric THz beam with uniform pulse shape for good focusability and high field strength.

Abstract-Single-cycle attosecond pulses by Thomson backscattering of terahertz pulses

György Tóth, Zoltán Tibai, Ashutosh Sharma, József A. Fülöp, and János Hebling

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-35-5-A103

The generation of single-cycle attosecond pulses based on Thomson scattering of terahertz (THz) pulses is proposed. In the scheme, a high-quality relativistic electron beam, produced by a laser-plasma wakefield accelerator, is sent through suitable magnetic devices to produce ultrathin electron layers for coherent Thomson backscattering of intense THz pulses. According to numerical simulations, single-cycle attosecond pulse generation is possible with up to 1 nJ energy. The waveform of the attosecond pulses closely resembles that of the THz pulses. This allows for flexible waveform control of attosecond pulses.

© 2018 Optical Society of America

Abstract-Single-cycle attosecond pulses by Thomson backscattering of terahertz pulses

György Tóth, Zoltán Tibai, Ashutos Sharma, József A. Fülöp, János Hebling

https://arxiv.org/abs/1711.05996

The generation of single-cycle attosecond pulses based on Thomson scattering of terahertz (THz) pulses is proposed. In the scheme, a high-quality relativistic electron beam produced by a laser-plasma wakefield accelerator (LPWA), is sent through suitable magnetic devices to produce ultrathin electron layers for coherent Thomson backscattering of intense THz pulses. According to numerical simulations, single-cycle attosecond pulse generation is possible with up to 1 nJ energy. The waveform of the attosecond pulses closely resembles that of the THz pulses. This allows for a flexible waveform control of attosecond pulses.

Abstract-Numerical investigation of a scalable setup for efficient terahertz generation using a segmented tilted-pulse-front excitation

László Pálfalvi, György Tóth, Levente Tokodi, Zsuzsanna Márton, József András Fülöp, Gábor Almási, and János Hebling

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-24-29560v

A hybrid-type terahertz pulse source is proposed for high energy terahertz pulse generation. It is the combination of the conventional tilted-pulse-front setup and a transmission stair-step echelon-faced nonlinear crystal with a period falling in the hundred-micrometer range. The most important advantage of the setup is the possibility of using plane parallel nonlinear optical crystal for producing good-quality, symmetric terahertz beam. Another advantage of the proposed setup is the significant reduction of imaging errors, which is important in the case of wide pump beams that are used in high energy experiments. A one dimensional model was developed for determining the terahertz generation efficiency, and it was used for quantitative comparison between the proposed new hybrid setup and previously introduced terahertz sources. With lithium niobate nonlinear material, calculations predict an approximately ten-fold increase in the efficiency of the presently described hybrid terahertz pulse source with respect to that of the earlier proposed setup, which utilizes a reflective stair-step echelon and a prism shaped nonlinear optical crystal. By using pump pulses of 50 mJ pulse energy, 500 fs pulse length and 8 mm beam spot radius, approximately 1% conversion efficiency and 0.5 mJ terahertz pulse energy can be reached with the newly proposed setup.

© 2017 Optical Society of America

Abstract-Periodically intensity-modulated pulses by optical parametric amplification for multicycle tunable terahertz pulse generation

György Tóth, József A. Fülöp, and János Hebling

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-23-28258

The superposition of signal and idler pulses in dual-chirped optical parametric amplification is proposed for the efficient generation of intensity-modulated pulses with periodic modulation. Both the duration and the modulation period are easily and independently adjustable. Numerical simulations for a three-stage optical parametric amplifier system predicted an efficiency as high as ~50% for about 40 mJ of output pulse energy at a wavelength of 2 µm. Sources of such intensity-modulated pulses near 1.6 µm or 2 µm wavelength, pumped by Ti:sapphire or Yb-doped lasers, can be ideally suited for intense multicycle THz pulse generation with tunable frequency and bandwidth by optical rectification for example in organic, semiconductor, or lithium niobate materials.

© 2017 Optical Society of America

Abstract-Refractive Index and Absorption Coefficient of Undoped and Mg-Doped Lithium Tantalate in the Terahertz Range

Andrea Buzády, Márta Unferdorben, György Tóth, János Hebling, Ivett Hajdara, László Kovács, László Pálfalvi

https://link.springer.com/article/10.1007%2Fs10762-017-0393-y

Dielectric material parameters of lithium tantalate (LT) in the terahertz region have been investigated using terahertz time-domain spectroscopy (THz-TDS). Undoped congruent, undoped stoichiometric, and Mg-doped stoichiometric LT crystals were measured. The Mg content was 0.5 and 1.0 mol% for the stoichiometric composition. Index of refraction and absorption coefficient spectra were determined in the 0.3–2.0-THz frequency range for beam polarization both parallel (extraordinary polarization) and perpendicular (ordinary polarization) to the optical axis [001] of the crystal at room temperature. For the calculation of the refractive index and absorption coefficient spectra from the measured data, we used TeraMat software (Menlo System) belonging to the spectrometer. The refractive index and the absorption coefficient for stoichiometric crystals were lower than for the congruent one. In the case of stoichiometric crystals, the Mg dopant caused a slight reduction of both ordinary and extraordinary refractive index compared to the undoped crystal. However, the presence of Mg did not reduce the absorption coefficient either for the ordinary or for the extraordinary polarization. In order to fit the measurement data, a Lorentz oscillator model was used. Good agreement was obtained between the measured data and the fitting curves by using the Lorentz oscillator model containing three terms.