2022-07-15, Schönfeld, Christoph, Sulzer, Philipp, Brida, Daniele, Leitenstorfer, Alfred, Kurihara, Takayuki

A single-cycle light source in the near infrared is demonstrated enabling sensitive applications of ultrafast optical field control of electronic transport. The compact Er:fiber system generates passively phase-locked pulses with broadband spectra covering 150 THz to 350 THz at a duration of 4.2 fs and 40 MHz repetition rate. A second output arm is equipped with an electro-optic modulator that switches the arrival time of the pulses by 700 ps at arbitrary frequencies up to 20 MHz, enabling timing modulation of the pump pulse without changing the average intensity. As a benchmark demonstration, we investigate the carrier relaxation dynamics in low-temperature-grown InGaAs using quantum interference currents.

2021, Allerbeck, Jonas, Deckert, Thomas, Kurihara, Takayuki, Brida, Daniele

Noncollinear two-dimensional spectroscopy in the 10-40 THz range enables background-free and phase-sensitive investigation of coherent low-energy dynamics in semiconductors and strongly correlated materials in a perturbative excitation regime. Measurements on bulk indium antimonide explore the capabilities of the setup and pave the way toward the investigation of functional thin film materials and few-layer samples.

2020-04-30, Kurihara, Takayuki, Hirota, Kazumasa, Qiu, Hongsong, Phan, Khoa Thanh Nhat, Kato, Kosaku, Isoyama, Goro, Nakajima, Makoto

Understanding the interaction between intense terahertz (THz) electromagnetic fields and spin systems has been gaining importance in modern spintronics research as a unique pathway to realize ultrafast macroscopic magnetization control. In this work, we used intense THz pulses with pulse energies in the order of 10 mJ/pulse generated from the terahertz free electron laser (THz-FEL) to irradiate the ferromagnetic domains of ErFeO3 single crystal. It was found that the domain shape can be locally reconfigured by irradiating the THz - FEL pulses near the domain boundary. Observed domain reconfiguration mechanism can be phenomenologically understood by the combination of depinning effect and the entropic force due to local thermal gradient exerted by terahertz irradiation. Our finding opens up a new possibility of realizing thermal-spin effects at THz frequency ranges by using THz-FEL pulses.

2018-09-10, Kurihara, Takayuki, Qiu, Hongsong, Kato, Kosaku, Watanabe, Hiroshi, Nakajima, Makoto

Due to its efficient coupling with electron spins, the application of terahertz magnetic nearfield in metallic microstructures has been attracting attention. While paramagnetic materials that exhibit magneto-optical effect have been known to enable visualization of the terahertz magnetic fields (magneto-optical sampling), the low field-detection sensitivity has been setting a practical limit to the broader application of such a method. Here we propose and experimentally demonstrate that the terahertz magnetic nearfield-detection sensitivity of magneto-optical sampling with terbium-gallium-garnet crystal can be drastically enhanced by cooling the crystal down to cryogenic temperatures in accordance with Curie's law. Our result paves the way for the efficient characterization of the terahertz magnetic nearfield in planer metamaterials.

2022, Kurihara, Takayuki, Fitzky, Gabriel, Leitenstorfer, Alfred, Nakajima, Makoto

We excite ultrafast spin reorientation in orthoferrite Sm_0.7Er_0.3FeO₃ in the mid-infrared by resonant f-f electronic transition or phononic pumping. The instantaneous onset of reorientation by electronic pumping suggests femtosecond nonthermal modification of magnetic anisotropy.

2021, Fitzky, Gabriel, Nakajima, Makoto, Koike, Yohei, Leitenstorfer, Alfred, Kurihara, Takayuki

We compare the ultrafast dynamics of the spin reorientation transition in the orthoferrite Sm_0.7Er_0.3FeO₃ following two different pumping mechanisms. Intense few-cycle pulses in the midinfrared selectively excite either the f−f electronic transition of Sm³⁺ or optical phonons. With phonon pumping, a finite time delay exists for the spin reorientation, reflecting the energy transfer between the lattice and 4f system. In contrast, an instantaneous response is found for resonant f−f excitation. This suggests that 4f electronic pumping can directly alter the magnetic anisotropy due to the modification of 4f−3d exchange at femtosecond timescales, without involving lattice thermalization.

2019, Allerbeck, Jonas, Spitzner, Laurens, Kurihara, Takayuki, Leitenstorfer, Alfred, Brida, Daniele

Two-dimensional spectroscopy employing an asymmetric scheme with visible excitation and multi-THz readout is applied to study ultrafast carrier dynamics in graphite, enabling phase sensitive investigation of correlations between high- and low-energy excitations.

2021, Fitzky, Gabriel, Nakajima, Makoto, Koike, Yohei, Leitenstorfer, Alfred, Kurihara, Takayuki

We report on the ultrafast dynamics of spin reorientation using different excitation mechanisms in the orthoferrite Sm 0.7 Er 0.3 FeO 3 . First, intense few-cycle mid-infrared pulses tuned to optical phonon resonance are exploited to excite the lattice system. A finite time delay of the spin reorientation is observed at its initial dynamics, displaying the energy transfer between lattice and 4f system. In contrast, an instantaneous response is found when the f-f electronic transition of Sm 3+ is resonantly excited. Our results indicate that 4f electronic pumping can alter the magnetic anisotropy due to the modification of 4f-3d exchange at femtosecond time scales, without involving lattice thermalization.

2021, Deckert, Thomas, Allerbeck, Jonas, Spitzner, Laurens, Kurihara, Takayuki, Brida, Daniele

Noncollinear two-dimensional spectroscopy in the mid infrared enables phase-sensitive investigation of coherent low-energy dynamics in semiconductors and strongly correlated materials in a perturbative excitation regime as shown by preliminary measurements on indium antimonide.

2018-11-20, Woldegeorgis, Abel, Kurihara, Takayuki, Almassarani, Mohammed, Beleites, Burgard, Grosse, Ronny, Ronneberger, Falk, Gopal, Amrutha

Longitudinally polarized terahertz radiation offers access to the elementary excitations and particles that cannot be addressed by transverse waves. While transverse electric fields exceeding 1 MV/cm are widely utilized for nonlinear terahertz spectroscopy, longitudinally polarized terahertz waves at this field strength are yet to be realized. In this paper, we experimentally demonstrate that by focusing radially polarized terahertz fields generated from laser–thin metallic foil interaction, longitudinally polarized terahertz with record-breaking field strength above 1.5 MV/cm can be obtained. Furthermore, we also traced the evolution of the geometric phase of the longitudinal component as it propagates through focus. A novel scheme based on noncollinear electro-optic detection has been utilized to unambiguously measure the polarization states. Our result will scale up the nonlinear spectroscopy of solid materials and particle acceleration experiments where on-axis polarization plays a crucial role.