József András Fülöp

ELI-ALPS Research Institute

We report a semiconductor contact grating terahertz source design based on a rectangular profile for phase-matched terahertz generation in the long infrared pump wavelength range. The calculations show that the best diffraction efficiency can be achieved by a filling factor significantly smaller than 50%. Furthermore, the possibility of diffraction...

A novel THz source, based on optical rectification in LiNbO3 using the tilted-pulse-front technique, is proposed and experimentally demonstrated. The pulse-front tilt is introduced by a volume phase holographic grating, efficiently used at perpendicular incidence in transmission, and the THz pulses are produced in a LiNbO3 plane-parallel nonlinear...

The transmission of THz, near-infrared (1030 nm), and green (515 nm) pulses through Eisenia andrei body wall is studied, which consists of epithelial layer and circular and longitudinal muscles. Samples with the full-body cross-section were also investigated. The transmitted power for the green pulses followed the Beer-Lambert law of exponential at...

A hybrid mechanism of ion acceleration is investigated which demonstrates the higher spectral density of protons at high energies. The interaction of few-cycle terrawatt laser pulses with near-critical density gas target is studied with the help of two-dimensional particle-in-cell simulation. The generation of few MeV protons with high spectral con...

A THz-pulse-driven compact, < 150 mm in total length, two-stage electron accelerator setup was designed. It uses 2 × 2 pairs of nearly counter-propagating focused THz pulses. The effects of the initial bunch charge and the propagation direction of the THz pulses on the energy of the accelerated electrons were investigated by numerical simulations....

Terahertz (THz) irradiation of excised Eisenia andrei earthworms is shown to cause overriding the genetically determined, endogenously mediated segment renewing capacity of the model animal. Single-cycle THz pulses of 5 µJ energy, 0.30 THz mean frequency, 293 kV/cm peak electric field, and 1 kHz repetition rate stimulated the cell proliferation (in...

Amplified bursts of laser pulses are sought for various machining, deposition, spectroscopic, and strong-field applications. Standard frequency- and time-domain techniques for pulse division become inadequate when intraburst repetition rates reach the terahertz (THz) range as a consequence of inaccessible spectral resolution, requirement for interf...

Two aminopyridinium based novel organic materials, 2-amino-5-nitropyridinium p-phenolsulfonate (2A5NPP) and 2,6-diaminopyridinium-4-nitrophenolate-4-nitrophenol (DAP⁺NP⁻NP) were characterized in the 0–2 THz range by time-domain terahertz (THz) spectroscopy. Density functional theory calculations were carried out to find the molecular vibrational mo...

Amplified bursts of laser pulses are sought for various machining, deposition, spectroscopic and strong-field applications. Standard frequency- and time-domain techniques for pulse division become inadequate when intraburst repetition rates reach the terahertz (THz) range as a consequence of inaccessible spectral resolution, requirement for interfe...

Intensity-dependent effective four-photon absorption (4PA) coefficients in GaP and ZnTe semiconductors were measured by the z-scan method using pump pulses of 1.75 µm wavelength, 135 fs duration, and up to 500 GWcm-2 intensity. A nonlinear pulse propagation model, including linear dispersion and 4PA was used to obtain the 4PA coefficients from meas...

We demonstrate generation of continuously-tunable, narrowband THz pulses from phase- locked multi-millijoule femtosecond pulse bursts by optical rectification in a tilted-pulse-front setup. Experimental results indicate advances in both, femtosecond pulse burst and high-energy THz source technology.

We demonstrate generation of continuously-tunable, narrowband THz pulses from phase-locked multi-millijoule femtosecond pulse bursts by optical rectification in a tilted-pulse-front setup. Experimental results indicate advances in both, femtosecond pulse burst and high-energy THz source technology.

Effective four-photon absorption coefficients and their anizotropy were meas-ured in semiconductors (ZnTe, GaP) by z-scan technique in infrared wavelength.

Simulations of contact grating design parameters in the wavelength range of 1.76-3.9 µm are presented for gallium arsenide and gallium phosphide. Diffraction efficiencies as high as 80% and 90% have been achieved in GaAs and GaP respectively.

We demonstrate generation of continuously-tunable, narrowband THz pulses from phase-locked multi-millijoule femtosecond pulse bursts by optical rectification in a tilted-pulse-front setup. Experimental results indicate advances in both femtosecond pulse burst and high-energy THz source technology.

A review on the recent development of intense laser‐driven terahertz (THz) sources is provided here. The technologies discussed include various types of sources based on optical rectification (OR), spintronic emitters, and laser‐filament‐induced plasma. The emphasis is on OR using pump pulses with tilted intensity front. Illustrative examples of ne...

A tilted-pulse-front pumped terahertz pulse source is proposed for the generation of extremely high field single-cycle terahertz pulses. The very simple and compact source consists of a single crystal slab having a blazed reflection grating grooved in its back surface. Its further important advantages are the energy scalability and the symmetric TH...

A tilted-pulse-front pumped terahertz pulse source is proposed for the generation of extremely high field single-cycle terahertz pulses. The very simple and compact source consists of a single crystal slab having a blazed reflection grating grooved in its back surface. Its further important advantages are the energy scalability and the symmetric TH...

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 conventi...

A new type of tilted-pulse-front pumped terahertz (THz) source has been demonstrated, which is based on a LiNbO3plane-parallel slab with an echelon structure on its input surface. Single-cycle pulses of 1 μJ energy and 0.30 THz central frequency have been generated with 5×10−4 efficiency from such a source. One order-of-magnitude increase in effici...

Taking advantage of the tunable conductivity of graphene under high terahertz (THz) electric field, a graphene-metal hybrid metamaterial consisting of an array of three adjoined orthogonally oriented split-ring resonators (SRRs) is proposed and experimentally demonstrated to show a maximum modulation depth of 23% in transmission when the THz peak f...

THz pulse generation in a nonlinear optical slab with an entrance surface having an echelon structure is demonstrated. The setup uses a transmission grating and a planeparallel lithium-niobate crystal slab, and ensures a good-quality, symmetric THz beam and enables scalability to high pulse energies.

We generate fully controllable fs multimillijoule pulse bursts with the energy handling, throughput efficiency and frequency resolution substantially exceeding that achievable in spatial-light-modulator and interferometric techniques. The demonstrated proof-of-concept experiments include coherent control of nitrogen-ion emission via multiple-pulse...

We demonstrate phase-controlled pulse-burst amplification based on differential pathlength stabilization between the master oscillator and the amplifier cavities. This technique boosts the safe level of extractable burst energy and suppresses fluctuations in various burst-mode applications.

Intensity-dependent four-photon absorption coefficients of Gallium-Phosphide (GaP) and Zink-Telluride (ZnTe) have been measured by the z-scan method at 1.75 μm pump wavelength. Anisotropy in the effective four-photon absorption has been shown in GaP.

Novel compact LiNbO3 and semiconductor THz sources, based on the tilted-pulse-front technique, enable straightforward scaling to unprecedented focused field strengths up to 50 MV/cm in the low-frequency part of the THz spectrum.

Practical aspects of the robust method we proposed for producing few-cycle attosecond pulses with arbitrary waveform in the extreme ultraviolet spectral range are studied numerically. It is based on the undulator radiation of relativistic ultrathin electron layers produced by laser-driven energy modulation. By using realistic specifications, we sho...

A relativistic electron source is proposed, driven by the wakefield of an intense terahertz (THz) pulse in low-density gas plasma. In contrast to the optical and near-infrared regimes, the low (3.5 THz) frequency and the long (λ T = 85.6 μm) wavelength of the THz pulse offers distinct advantages, such as the -scaling of the electron ponderomotive e...

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 i...

The acceleration of single electrons and electron bunches by focused THz pulse pairs has been investigated by numerical simulations. The effect of the choice of the beam waist radius, the carrier-envelope phase, and the propagation direction of the THz pulses on the energy of the accelerated electrons was investigated. The acceleration of electron...

Multicycle THz pulse generation by optical rectification in GaP semiconductor nonlinear material is investigated by numerical simulations. It is shown that GaP can be an efficient and versatile source with up to about 8% conversion efficiency and a tuning range from 0.1 THz to about 7 THz. Contact-grating technology for pulse-front tilt can ensure...

Applying a standard earthworm tail segment regeneration model the effects of THz pulses were investigated on the segment formation kinetic and characteristic histological alterations in Eisenia Andrei after 25 tail segments removal. After the surgical intervention, the last 4-5 segments located close to the transection were exposed to THz pulses wi...

Because of their suitable wavelength and temporal period, THz pulses with extremely high field strength are ideal for driving particle accelerators. Here we give an overview of the possibilities and challenges of THz-pulse-driven electron post accelerators.

A monolithic contact-grating semiconductor source and a hybrid LiNbO3 stair-step echelon are presented for efficient THz pulse generation by optical rectification. They enable excellent focusability of the THz beams and are scalable to mJ-level THz pulse energies.

A laser-plasma accelerator based carrier-envelope-phase stable attosecond source is investigated numerically. Pulses with tens-of-nJ energy and 90 to 240 attosecond duration are predicted in the 30-120 nm wavelength range.

DC-OPA is proposed for generation of periodically intensity-modulated-pulses by interference of the signal and the idler. These pulses allows to tunable THz-pulse generation by the chirp and the delay between the pump and the signal.

According to calculations, single-cycle attosecond pulses can be generate with few nJ energy by Thomson scattering of terahertz pulse on ultrathin electron layer, produced by a laser-plasma wakefield accelerator and some suitable magnetic devices.

Up to 5% conversion efficiency is predicted by numerical simulations for optimized GaP contact-grating THz sources based on optical rectification. Easy control of multicycle THz waveforms is enabled by a flexible dual-chirped OPA pump source.

A nonlinear echelon slab structure is proposed for high-energy THz pulse generation. The most important advantage of the setup is the possibility of using plane parallel nonlinear optical crystal for producing good-quality, symmetric THz beam.

Single-cycle attosecond pulses can be generate by Thomson scattering of terahertz pulses on ultrathin electron layers, produced by a laser-plasma wakefield accelerator. According to our calculations, the energy can achieve more than 1 nJ.

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 pla...

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 in...

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 syste...

Laser-driven proton acceleration from micron-sized cryogenic hydrogen microjet target is investigated using multi-dimensional particle-in-cell simulations. The simulations reproduce well the proton energy spectrum measured at the Titan laser with 700-fs long pulses [23]. High-energy quasi-monoenergetic proton acceleration is predicted in a new regi...

Laser-plasma accelerators (LPAs), producing high-quality electron beams, provide an opportunity to reduce the size of free-electron lasers (FELs) to only a few meters. A complete system is proposed here, which is based on FEL technology and consists of an LPA, two undulators, and other magnetic devices. The system is capable to generate carrier-env...

Globally, large international research infrastructures have over many decades promoted excellence in science and technology. Aligned with the international practice, the Europe Strategy Forum for Research Infrastructures (ESFRI) has developed and keeps updating a roadmap for research infrastructures. The Extreme Light Infrastructure (ELI) is one of...

We report on a diode-pumped cryogenically cooled bulk Yb:CaF2 12-pass amplifier delivering 110-mJ, 1030-nm pulses at a 50-Hz repetition rate. The pulses have a spectral bandwidth of 13 nm and are compressed to 225 fs pulse duration in a double reflection grating based compressor having a transmission efficiency of >90%. The measured output beam qua...

Intense pulses at low terahertz (THz) frequencies of 0.1–2THz 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,...