FPGA-based measurements of the relative arrival time of a high-repetition rate, quasi-cw fourth generation light source.

In this paper, we demonstrate the successful implementation of reconfigurable field-programmable gate array technology into a pulse-resolved data acquisition system to achieve a femtosecond temporal resolution in ultrafast pump-probe experiments in real-time at large scale facilities. As proof of concept, electro-optic sampling of terahertz waveforms radiated by a superradiant emitter of a quasi-cw accelerator operating at a 50 kHz repetition rate and probed by an external laser system is performed. Options for up-scaling the developed technique to a MHz range of repetition rates are discussed.

Terahertz magneto-optical sampling in quartz glass.

In this Letter, we demonstrate terahertz (THz) magnetic field detection in fused silica with sensitivity that can be easily controlled by sample tilting (for both amplitude and polarization). The proposed technique remains in the linear regime at magnetic fields exceeding 0.3 T (0.

Magnon-phonon Fermi resonance in antiferromagnetic CoF.

Understanding spin-lattice interactions in antiferromagnets is a critical element of the fields of antiferromagnetic spintronics and magnonics. Recently, coherent nonlinear phonon dynamics mediated by a magnon state were discovered in an antiferromagnet. Here, we suggest that a strongly coupled two-magnon-one phonon state in this prototypical system opens a novel pathway to coherently control magnon-phonon dynamics.

Tracing the dynamics of superconducting order via transient terahertz third-harmonic generation.

Ultrafast optical control of quantum systems is an emerging field of physics. In particular, the possibility of light-driven superconductivity has attracted much of attention. To identify nonequilibrium superconductivity, it is necessary to measure fingerprints of superconductivity on ultrafast timescales.

Efficient ultrafast field-driven spin current generation for spintronic terahertz frequency conversion.

Efficient generation and control of spin currents launched by terahertz (THz) radiation with subsequent ultrafast spin-to-charge conversion is the current challenge for the next generation of high-speed communication and data processing units. Here, we demonstrate that THz light can efficiently drive coherent angular momentum transfer in nanometer-thick ferromagnet/heavy-metal heterostructures. This process is non-resonant and does neither require external magnetic fields nor cryogenics.

A universal route to efficient non-linear response via Thomson scattering in linear solids.

Non-linear materials are cornerstones of modern optics and electronics. Strong dependence on the intrinsic properties of particular materials, however, inhibits the at-will extension of demanding non-linear effects, especially those second-order ones, to widely adopted centrosymmetric materials (for example, silicon) and technologically important burgeoning spectral domains (for example, terahertz frequencies). Here we introduce a universal route to efficient non-linear responses enabled by exciting non-linear Thomson scattering, a fundamental process in electrodynamics that was known to occur only in relativistic electrons in metamaterial composed of linear materials.

Nanopatterning of the dielectric surface by a pair of femtosecond laser pulses of different colors through a monolayer of microspheres.

This paper considers the nanostructuring of the surface of dielectrics under the effect of two successive femtosecond laser pulses, one of the fundamental frequency (FF) and the other of the second harmonic (SH) of a Ti:sapphire laser, through a layer of polystyrene microspheres 1 µm in diameter, which act as microlenses. Polymers with strong (PMMA) and weak (TOPAS) absorption at the frequency of the third harmonic of a Ti:sapphire laser (sum frequency FF + SH) were used as targets. Laser irradiation led to the removal of microspheres and the formation of ablation craters with characteristic dimensions of about 100 nm.

Ultrafast Tunable Terahertz-to-Visible Light Conversion through Thermal Radiation from Graphene Metamaterials.

Several technologies, including photodetection, imaging, and data communication, could greatly benefit from the availability of fast and controllable conversion of terahertz (THz) light to visible light. Here, we demonstrate that the exceptional properties and dynamics of electronic heat in graphene allow for a THz-to-visible conversion, which is switchable at a sub-nanosecond time scale. We show a tunable on/off ratio of more than 30 for the emitted visible light, achieved through electrical gating using a gate voltage on the order of 1 V.

Fano interference between collective modes in cuprate high-T superconductors.

Cuprate high-T superconductors are known for their intertwined interactions and the coexistence of competing orders. Uncovering experimental signatures of these interactions is often the first step in understanding their complex relations. A typical spectroscopic signature of the interaction between a discrete mode and a continuum of excitations is the Fano resonance/interference, characterized by the asymmetric light-scattering amplitude of the discrete mode as a function of the electromagnetic driving frequency.

Field-resolved THz-pump laser-probe measurements with CEP-unstable THz light sources.

Radiation sources with a stable carrier-envelope phase (CEP) are highly demanded tools for field-resolved studies of light-matter interaction, providing access both to the amplitude and phase information of dynamical processes. At the same time, many coherent light sources, including those with outstanding power and spectral characteristics lack CEP stability, and so far could not be used for this type of research. In this work, we present a method enabling linear and non-linear phase-resolved terahertz (THz) -pump laser-probe experiments with CEP-unstable THz sources.

Milliwatt terahertz harmonic generation from topological insulator metamaterials.

Achieving efficient, high-power harmonic generation in the terahertz spectral domain has technological applications, for example, in sixth generation (6G) communication networks. Massless Dirac fermions possess extremely large terahertz nonlinear susceptibilities and harmonic conversion efficiencies. However, the observed maximum generated harmonic power is limited, because of saturation effects at increasing incident powers, as shown recently for graphene.

Terahertz-slicing - an all-optical synchronization for 4 generation light sources.

A conceptually new approach to synchronizing accelerator-based light sources and external laser systems is presented. The concept is based on utilizing a sufficiently intense accelerator-based single-cycle terahertz pulse to slice a thereby intrinsically synchronized femtosecond-level part of a longer picosecond laser pulse in an electro-optic crystal. A precise synchronization of the order of 10 fs is demonstrated, allowing for real-time lock-in amplifier signal demodulation.

Experimental observation of optically generated unipolar electromagnetic precursors.

It was recently predicted [Phys. Rev. A95(6), 063817 (2017) 10.

Efficient optical-to-terahertz conversion in large-area InGaAs photo-Dember emitters with increased indium content.

In this Letter, optical-to-terahertz (THz) conversion of 800 nm femtosecond laser pulses in large-area bias-free InGaAs emitters based on photo-Dember (PD) and lateral photo-Dember (LPD) effects is experimentally investigated. We use metamorphic buffers to grow sub-micrometer thick layers with indium mole fractions =0.37, 0.

Electrical tunability of terahertz nonlinearity in graphene.

Graphene is conceivably the most nonlinear optoelectronic material we know. Its nonlinear optical coefficients in the terahertz frequency range surpass those of other materials by many orders of magnitude. Here, we show that the terahertz nonlinearity of graphene, both for ultrashort single-cycle and quasi-monochromatic multicycle input terahertz signals, can be efficiently controlled using electrical gating, with gating voltages as low as a few volts.

Grating-Graphene Metamaterial as a Platform for Terahertz Nonlinear Photonics.

Nonlinear optics is an increasingly important field for scientific and technological applications, owing to its relevance and potential for optical and optoelectronic technologies. Currently, there is an active search for suitable nonlinear material systems with efficient conversion and a small material footprint. Ideally, the material system should allow for chip integration and room-temperature operation.

Non-perturbative terahertz high-harmonic generation in the three-dimensional Dirac semimetal CdAs.

Harmonic generation is a general characteristic of driven nonlinear systems, and serves as an efficient tool for investigating the fundamental principles that govern the ultrafast nonlinear dynamics. Here, we report on terahertz-field driven high-harmonic generation in the three-dimensional Dirac semimetal CdAs at room temperature. Excited by linearly-polarized multi-cycle terahertz pulses, the third-, fifth-, and seventh-order harmonic generation is very efficient and detected via time-resolved spectroscopic techniques.

Phase-resolved Higgs response in superconducting cuprates.

In high-energy physics, the Higgs field couples to gauge bosons and fermions and gives mass to their elementary excitations. Experimentally, such couplings can be inferred from the decay product of the Higgs boson, i.e.

Highly efficient Cherenkov-type terahertz generation by 2-μm wavelength ultrashort laser pulses in a prism-coupled LiNbO layer.

Terahertz generation by optical rectification of femtosecond laser pulses propagating in a 40-m thick LiNbO layer attached to an output Si prism has been experimentally investigated for different laser wavelengths from 800 to 2100 nm. For longer wavelengths, the saturation of the optical-to-terahertz conversion efficiency has been observed at higher laser pulse energies, thus enabling higher efficiencies. In particular, record high conversion efficiency of 1.

Pulse- and field-resolved THz-diagnostics at 4 generation lightsources.

Multi-color pump-probe techniques utilizing modern accelerator-based 4th generation light sources such as X-ray free electron lasers or superradiant THz facilities have become important science drivers over the past 10 years. In this type of experiments the precise knowledge of the properties of the involved accelerator-based light pulses crucially determines the achievable sensitivity and temporal resolution. In this work we demonstrate and discuss the powerful role pulse- and field-resolved- detection of superradiant THz pulses can play for improving the precision of THz pump - femtosecond laser probe experiments at superradiant THz facilities in particular and at 4th generation light sources in general.

Electro-optic sampling of terahertz waves by laser pulses with an edge-cut spectrum in birefringent crystal.

We demonstrate a terahertz detection technique based on variations of the energy of femtosecond laser pulses with an edge-cut spectrum in birefringent electro-optic crystal-periodically poled lithium niobate (PPLN). The method is compared with the standard electro-optic detection scheme utilizing GaP crystal. The experimental results show that the studied technique is suited for use with birefringent crystals and allows one to achieve a much better response to the terahertz wave radiation at quasi-phase-matching frequencies of PPLN.

Terahertz radiation from bismuth surface induced by femtosecond laser pulses.

We report on the first experimental observation of terahertz (THz) wave generation from bismuth mono- and polycrystalline samples irradiated by femtosecond laser pulses. Dependencies of the THz signal on the crystal orientation, optical pulse energy, incidence angle, and polarization are presented and discussed together with features of the sample surfaces. The optical-to-THz conversion efficiency was up to two orders of magnitude higher than for metal at a moderate fluence of ∼1  mJ/cm.

Terahertz time-domain electro-optic measurements by femtosecond laser pulses with an edge-cut spectrum.

Balanced electro-optic detection techniques of terahertz wave radiation are proposed based on variations of the energy and ellipticity of laser pulses with an edge-cut spectrum. The techniques are compared with the standard electro-optic detection scheme utilizing laser pulses with Gaussian spectrum shape. Our calculations and measurements show that the studied schemes have a much better response to the terahertz wave radiation at high frequencies compared with the standard one.

Colloidal particle lens arrays-assisted nano-patterning by harmonics of a femtosecond laser.

We consider nanopatterning of dielectric substrates by harmonics of single powerful femtosecond pulses from a Ti:Sapphire laser. The nanopatterning is mediated by closely packed monolayers of polystyrene microspheres that act as microlenses at the surface. Observed modification of the material proceeds via ionization.

Terahertz emission from a metallic surface induced by a femtosecond optic pulse.

Results of experimental and theoretical investigations on generation of terahertz radiation at the interaction of femtosecond laser pulses with a metal surface are presented. Investigations are performed with the laser pulse intensities higher compared with that used in papers [Opt. Lett.