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Fulop J.A.,MTA PTE High Field Terahertz Research Group | Fulop J.A.,University of Pécs | Ollmann Z.,University of Pécs | Lombosi C.S.,University of Pécs | And 10 more authors.
Optics Express | Year: 2014

Efficient generation of THz pulses with high energy was demonstrated by optical rectification of 785-fs laser pulses in lithium niobate using tilted-pulse-front pumping. The enhancement of conversion efficiency by a factor of 2.4 to 2.7 was demonstrated up to 186 μJ THz energy by cryogenic cooling of the generating crystal and using up to 18.5 mJ/cm2 pump fluence. Generation of THz pulses with more than 0.4 mJ energy and 0.77% efficiency was demonstrated even at room temperature by increasing the pump fluence to 186 mJ/cm2. The spectral peak is at about 0.2 THz, suitable for charged-particle manipulation. © 2014 Optical Society of America.


Schneider W.,Ludwig Maximilians University of Munich | Schneider W.,Max Planck Institute of Quantum Optics | Ryabov A.,Ludwig Maximilians University of Munich | Ryabov A.,Max Planck Institute of Quantum Optics | And 7 more authors.
Optics Letters | Year: 2014

Yb:YAG thin-disk lasers offer extraordinary output power, but systems delivering femtosecond pulses at a repetition rate of hundreds of kilohertz are scarce, even though this regime is ideal for ultrafast electron diffraction, coincidence imaging, attosecond science, and terahertz (THz) spectroscopy. Here we describe a regenerative Yb:YAG amplifier based on thin-disk technology, producing 800-fs pulses at a repetition rate adjustable between 50 and 400 kHz. The key design elements are a short regenerative cavity and fast-switching Pockels cell. The average output power is 130 Wbefore the compressor and 100 W after compression, which at 300 kHz corresponds to pulse energies of 430 and 330 μJ, respectively. This is sufficient for a wide range of nonlinear conversions and broadening/compression schemes. As a first application, we use optical rectification in LiNbO3 to produce 30-nJ single-cycle THz pulses with 6W pump power. The electric field exceeds 10 kV/cm at acentral frequency of 0.3 THz, suitable for driving structural dynamics or controlling electron beams. © 2014 Optical Society of America.


Tibai Z.,University of Pécs | Toth Gy.,University of Pécs | Mechler M.I.,MTA PTE High Field Terahertz Research Group | Fulop J.A.,MTA PTE High Field Terahertz Research Group | And 5 more authors.
Physical Review Letters | Year: 2014

A robust method for producing half-cycle-few-cycle attosecond pulses in the extreme ultraviolet spectral range is proposed. It is based on coherent undulator radiation of relativistic ultrathin electron layers (nanobunches), which are produced by nanobunching of ultrashort electron bunches by a 10-TW power laser in a modulator undulator. Our numerical calculations predict the generation of nanobunches shorter than 10 nm. By using these electron nanobunches the production of carrier-envelope-phase stable attosecond pulses with up to a few tens of nJ energy and down to 10 nm wavelength and 35 as duration is predicted. © 2014 American Physical Society.


Palfalvi L.,University of Pécs | Fulop J.A.,MTA PTE High Field Terahertz Research Group | Toth Gy.,University of Pécs | Hebling J.,University of Pécs | Hebling J.,MTA PTE High Field Terahertz Research Group
Physical Review Special Topics - Accelerators and Beams | Year: 2014

Hadron therapy motivates research dealing with the production of particle beams with ∼100MeV/nucleon energy and relative energy fluctuation on the order of 1%. Laser-driven accelerators produce ion beams with only tens of MeV/nucleon energy and an extremely broad spectra. Here, a novel method is proposed for postacceleration and monochromatization of particles, leaving the laser-driven accelerator, by using intense THz pulses. It is based on further developing the idea of using the evanescent field of electromagnetic waves between a pair of dielectric crystals. Simple model calculations show that the energy of a proton bunch can be increased from 40 to 56 MeV in five stages and its initially broad energy distribution can be significantly narrowed down. © 2014 Published by the American Physical Society.


Adam P.,Hungarian Academy of Sciences | Adam P.,University of Pécs | Mechler M.,MTA PTE High Field Terahertz Research Group | Szalay V.,Hungarian Academy of Sciences | Koniorczyk M.,University of Pécs
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

Recently a new uncertainty relation was found as an alternative to a number-phase uncertainty relation for a harmonic oscillator. In this paper we determine numerically, via the discrete-variable-representation method known from quantum chemistry, the exact states that saturate this new uncertainty relation. We analyze the physical properties of the states and compare them to the intelligent states of the Pegg-Barnett uncertainty relation. We find that for a given set of expectation values of the physical parameters, which are the particle number and the two quadratures, the two kinds of intelligent states are equivalent. The intelligent states are the eigenstates corresponding to the lowest eigenvalue of a Hermitian operator, which, when interpreted as a Hamiltonian of a physical sytem, describes a nonlinear driven harmonic oscillator, for example, a Duffing oscillator for a certain parameter range. Hence, our results can be interpreted as the determination of the ground state of such physical systems in an explicit analytic form as well. As the Pegg-Barnett intelligent states we use are expressed in terms of a coherent-state superposition facilitating experimental synthesis, we relate the states determined here to experimentally feasible ones. © 2014 American Physical Society.


Lombosi C.,University of Pécs | Polonyi G.,University of Pécs | Mechler M.,MTA PTE High Field Terahertz Research Group | Ollmann Z.,University of Pécs | And 4 more authors.
New Journal of Physics | Year: 2015

Near- and far-field beam profiles were measured for THz pulses generated in LiNbO3 by optical rectification of 200 fs pulses with a tilted pulse front. The variation of the THz beam size and a dramatically increasing divergence angle with increasing pump fluence were observed in the (horizontal) plane of the pulse front tilt. No significant variation was observed in the vertical direction. The reason for the observed nonlinear beam distortion is the shortening of the effective interaction length for THz generation caused by the combined effect of pump spectral broadening and angular dispersion in the tilted pulse front geometry. Our results indicate that nonlinear THz beam distortion effects have to be taken into account when designing intense THz sources and related experiments. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Adam P.,Hungarian Academy of Sciences | Adam P.,University of Pécs | Mechler M.,MTA PTE High Field Terahertz Research Group | Santa I.,University of Pécs | Koniorczyk M.,University of Pécs
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We introduce a theoretical framework which is suitable for the description of all spatial and time-multiplexed periodic single-photon sources realized or proposed thus far. Our model takes into account all possibly relevant loss mechanisms. This statistical analysis of the known schemes shows that multiplexing systems can be optimized in order to produce maximal single-photon probability for various sets of loss parameters by the appropriate choice of the number of multiplexed units of spatial multiplexers or multiplexed time intervals and the input mean photon pair number and reveals the physical reasons of the existence of the optimum. We propose a time-multiplexed scheme to be realized in bulk optics, which, according to the present analysis, would have promising performance when experimentally realized. It could provide a single-photon probability of 85% with a choice of experimental parameters which are feasible according to the experiments known from the literature. © 2014 American Physical Society.


Ollmann Z.,University of Pécs | Fulop J.A.,MTA PTE High Field Terahertz Research Group | Hebling J.,University of Pécs | Hebling J.,MTA PTE High Field Terahertz Research Group | And 2 more authors.
Optics Communications | Year: 2014

A compact, particularly robust, and scalable high-energy THz pulse source is proposed based on optical rectification of femtosecond laser pulses in ZnTe by using a contact grating. It is shown by numerical calculations that diffraction efficiencies as high as 80% and 90% can be achieved with sinusoidal and binary contact grating profiles, respectively, in the 1.4-1.7 μm pump wavelength range, where no two-photon absorption is present, thereby allowing higher pump intensities. Detailed design parameters are given. The contact grating technology based on ZnTe or other semiconductors can be an efficient source of intense THz pulses with mJ-level energy. © 2013 Elsevier B.V.


Kovacs L.,Hungarian Academy of Sciences | Szaller Z.,Hungarian Academy of Sciences | Lengyel K.,Hungarian Academy of Sciences | Peter A.,Hungarian Academy of Sciences | And 5 more authors.
Optics Letters | Year: 2013

Several optical methods including ultraviolet absorption, infrared absorption of the hydroxyl ions, Raman spectroscopy, and the Z-scan method have been used to determine the damage resistance threshold in 0-0.72 mol. % Zr-containing, flux-grown, nearly stoichiometric LiNbO3 single crystals. All spectroscopical methods used indicate that samples containing at least ̃0.085 mol: % Zr in the crystal are above the threshold while Z-scan data locate the photorefractive damage threshold between 0.085 and 0.314 mol. % Zr. © 2013 Optical Society of America.


Vicario C.,Paul Scherrer Institute | Monoszlai B.,Paul Scherrer Institute | Monoszlai B.,University of Pécs | Lombosi C.,University of Pécs | And 5 more authors.
Optics Letters | Year: 2013

We present a study on THz generation in lithium niobate pumped by a powerful and versatile Yb:CaF2 laser. The unique laser system delivers transform-limited pulses of variable duration (0.38-0.65 ps) with pulse energies up to 15 mJ and center wavelength of 1030 nm. From previous theoretical investigations, it is expected that such laser parameters are ideally suited for efficient THz generation. Here, we present experimental results on both the conversion efficiency and the THz spectral shape for variable pump pulse durations and for different crystal temperatures, down to 25 K. We experimentally verify the optimum pump parameters for the most efficient and broadband THz generation. © 2013 Optical Society of America.

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