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.

Strong Terahertz Third-Harmonic Generation by Kinetic Heavy Quasiparticles in CaRuO_{3}.

We report on time-resolved nonlinear terahertz spectroscopy of a strongly correlated ruthenate, CaRuO_{3}, as a function of temperature, frequency, and terahertz field strength. Third-harmonic radiation for frequencies up to 2.1 THz is observed evidently at low temperatures below 80 K, where the low-frequency linear dynamical response deviates from the Drude model and a coherent heavy quasiparticle band emerges by strong correlations associated with the Hund's coupling.

Empowering Control of Antiferromagnets by THz-Induced Spin Coherence.

Finding efficient and ultrafast ways to control antiferromagnets is believed to be instrumental in unlocking their potential for magnetic devices operating at THz frequencies. Still, it is challenged by the absence of net magnetization in the ground state. Here, we show that the magnetization emerging from a state of coherent spin precession in antiferromagnetic iron borate FeBO_{3} can be used to enable the nonlinear coupling of light to another, otherwise weakly susceptible, mode of spin precession.

Two-dimensional terahertz spectroscopy as a tool for revealing nonlinear interactions in media.

Usually, the presence of multiple eigenstates (magnons and phonons) in a system makes it difficult to analyze the coupled excitation mechanism using conventional single-pulse terahertz (THz) spectroscopy. On the contrary, 2D THz spectroscopy reveals energy flows between these states, which facilitates the identification of the coupled dynamics. In this article, we provide a theoretical description of this advanced technique and an experimental demonstration of its performance in antiferromagnet CoF2.

Noncollinear electro-optic sampling detection of terahertz pulses in a LiNbO crystal while avoiding the effect of intrinsic birefringence.

We propose and experimentally prove efficient high-resolution electro-optic sampling measurement of broadband terahertz waveforms in a LiNbO crystal in the configuration with the probe laser beam propagating along the optical axis of the crystal. This configuration allows one to avoid the detrimental effect of strong intrinsic birefringence of LiNbO without any additional optical elements. To achieve velocity matching of the terahertz wave and the probe beam, the terahertz wave is introduced into the crystal through a Si prism at the Cherenkov angle to the probe beam.

Terahertz light-driven coupling of antiferromagnetic spins to lattice.

Understanding spin-lattice coupling represents a key challenge in modern condensed matter physics, with crucial importance and implications for ultrafast and two-dimensional magnetism. The efficiency of angular momentum and energy transfer between spins and the lattice imposes fundamental speed limits on the ability to control spins in spintronics, magnonics, and magnetic data storage. We report on an efficient nonlinear mechanism of spin-lattice coupling driven by terahertz light pulses.

THz-Scale Field-Induced Spin Dynamics in Ferrimagnetic Iron Garnets.

THz magnetization dynamics of antiferromagnetically coupled spins in ferrimagnetic Tm_{3}Fe_{5}O_{12} is excited by a picosecond single-cycle pulse of a magnetic field and probed with the help of the magneto-optical Faraday effect. Data analysis combined with numerical modeling shows that the dynamics corresponds to the exchange mode excited by the Zeeman interaction of the THz magnetic field with the spins. We argue that THz-pump-IR-probe experiments on ferrimagnets offer a unique tool for quantitative studies of dynamics and mechanisms to control antiferromagnetically coupled spins.

Terahertz Optomagnetism: Nonlinear THz Excitation of GHz Spin Waves in Antiferromagnetic FeBO_{3}.

A nearly single cycle intense terahertz (THz) pulse with peak electric and magnetic fields of 0.5  MV/cm and 0.16 T, respectively, excites both modes of spin resonances in the weak antiferromagnet FeBO_{3}.

Nonellipsometric electro-optic sampling of terahertz waves in GaAs.

We report efficient high-resolution electro-optic sampling detection of broadband terahertz radiation by measuring direct intensity modulation of a femtosecond fiber laser beam induced by terahertz field in a 1-cm thick GaAs crystal.

Asymmetric Cherenkov radiation for improved terahertz generation in the Si-prism-coupled LiNbO3 layer.

We show that a Cherenkov emission of terahertz waves from a femtosecond optical pulse propagating in a LiNbO(3) crystal can be strongly spatially asymmetric with respect to the direction of the optical pulse propagation. We propose using this phenomenon to improve the spectral characteristics of one of the most efficient optical-to-terahertz converters: a thin LiNbO(3) layer attached to a Si-prism outcoupler.

Terahertz difference-frequency generation by tilted amplitude front excitation.

To circumvent a velocity mismatch between optical pump and terahertz waves in electro-optic crystals, we propose to use dual-wavelength optical beams tilted with respect to their planes of equal amplitude. The tilt is achieved by transmission of a dual-wavelength laser beam through a diffraction grating placed on the crystal boundary. The proposed technique extends optical rectification of tilted-front femtosecond laser pulses to difference-frequency generation with longer (nanosecond) pulses.