Abstract-Broadband and narrowband laser-based terahertz source and its application for resonant and non-resonant excitation of antiferromagnetic modes in NiO

O. V. Chefonov, A. V. Ovchinnikov, C. P. Hauri, and M. B. Agranat

 Schematic diagram of a versatile THz source with tunable spectrum. (a) – the main elements of the laser system for generating optical pulses with different temporal shape. AODDL is an acousto-optic dispersion delay line, MZI is a Mach-Zehnder interferometer. (b), (c), (d) – examples of temporal shapes of laser pulses at the output of the temporal compressor. NC is a non-linear organic crystal for generating THz radiation (THz).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-19-27273

A versatile table-top high-intense source of terahertz radiation, enabling to generate pulses of both broadband and narrowband spectra with a tunable frequency up to 3 THz is presented. The terahertz radiation pulses are generated by optical rectification of femtosecond pulses of Cr:forsterite laser setup in nonlinear organic crystal OH1. Electric field strengths of broadband and narrowband terahertz pulses were achieved close to 20 MV/cm and more than 2 MV/cm, correspondingly. Experiments on excitation of spin subsystem oscillations of an antiferromagnetic NiO were carried out. Selective excitation of 0.42 THz mode was observed for the first time at room temperature by a narrowband terahertz pulses tuned close to mode frequency.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Photoinduced terahertz dynamics in BizSes topological insulator

 F. Giorgianni, M. Shalaby,   C. Vicario,  C. P. Hauri,  S. Lupi

http://ieeexplore.ieee.org/document/8087694/

Plasmons are collective charge density waves in a conductive material, which show remarkable electromagnetic properties and have great potential for photonics from terahertz to the ultraviolet. Besides the conventional plasmonic excitations in metals and in semiconductors, 2-dimensional (2D) plasmons of massless Dirac electrons have been observed in graphene and at the surface of topological insulators (TIs). TIs are quantum electronic materials with an insulating gap in the bulk originated by a strong spin-orbit coupling and Dirac metallic states at their interfaces. Among the various TIs, Bi2Se3 is one of the most promising material due to its large band gap Eg~300 meV. Recently, it has been shown that the low energy single particle and collective (plasmons) electrodynamics response are dominated by surface Dirac electrons in Bi2Se3 in steady state regime [1]. The relaxation dynamics show that an excess of electrons are continuously injected from bulk to the surface through surface states-bulk phonon scattering channel [2,3]. In this work we study the time resolved photoinduced THz dynamics of plasmonic response in micro-ribbons patterned Bi2Se3 thin film by means of optical-pump/THz-probe spectroscopy.

Abstract-Generation of 0.9-mJ THz pulses in DSTMS pumped by a Cr:Mg2SiO4 laser

C. Vicario, A. V. Ovchinnikov, S. I. Ashitkov, M. B. Agranat, V. E. Fortov, and C. P. Hauri  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-23-6632

Optics Letters, Vol. 39, Issue 23, pp. 6632-6635 (2014)
http://dx.doi.org/10.1364/OL.39.006632

We report on high-field terahertz transients with 0.9-mJ pulse energy produced in a 400  mm2 partitioned organic crystal by optical rectification of a 30-mJ laser pulse centered at 1.25 μm wavelength. The phase-locked single-cycle terahertz pulses cover the hard-to-access low-frequency range between 0.1 and 5 THz and carry peak fields of more than 42 MV/cm and 14 Tesla with the potential to reach over 80 MV/cm by choosing appropriate focusing optics. The scheme based on a Cr:Mg2SiO4 laser offers a high conversion efficiency of 3% using uncooled organic crystal. The collimated pump laser configuration provides excellent terahertz focusing conditions.

© 2014 Optical Society of America

Abstract-GV/m single-cycle terahertz fields from a laser-driven large-size partitioned organic crystal

C. Vicario, B. Monoszlai, and C. P. Hauri

https://journals.aps.org/prl/accepted/c7079Yf5Cf718537276d86f4c4bdf3efaa38d538e

We report on compact and efficient laser-based THz generation in the Terahertz frequency gap (1-10 THz). The radiation is generated by optical rectification of a mid-infrared laser in a large-size, partitioned nonlinear organic crystal assembly. This enables up-scaling of presently field-limited table-top THz sources to GV/m electric and several Tesla magnetic field at millijoule pulse energy. In agreement with simulations the THz beam properties at focus are shown to be not deteriorated by the discontinuity of the emitter surface. The high laser-to-THz energy conversion efficiency exceeds the Manley-Rowe limit and is explained by a cascaded chi^(2) process in the organic crystals accompanied by a significant red shift of the pump spectrum. The scheme provides a compact, table-top THz source for single-cycle transients at field strength equivalent or even higher to linear accelerator and FEL-based THz sources. This opens an avenue towards novel nonlinear THz applications.

Abstract-Off-resonant magnetization dynamics phase-locked to an intense phase-stable terahertz transient

 

                                                                 Time-resolved magneto-optical Kerr effect (MOKE) set-up
                                                                 that allows for the measurement of ultrafast moment dynamics
                                                                on a room-temperature cobalt sample surface.                                        
                                                                The strong 0.4 T single-cycle terahertz magnetic field (blue)
                                                                 is linearly polarized and carries an absolute phase, which remains
                                                                 constant for consecutive shots. The terahertz pump pulse hits the sample
                                                                 20° off-normal incidence.
C. Vicario,¹ C. Ruchert,¹ F. Ardana-Lamas,^{1, 2} P. M. Derlet,³ B. Tudu,⁴, J. Luning⁴,  C. P. Hauri^{1, 2}
http://www.nature.com/nphoton/journal/v7/n9/full/nphoton.2013.209.html

Controlling magnetization dynamics with a femtosecond laser is attracting interest both in fundamental science and in industry because of the potential to achieve magnetic switching at ever faster speeds. Here, we report a coherent, phase-locked coupling between a high-field single-cycle terahertz transient and the magnetization of ferromagnetic cobalt films. The visualized magnetization dynamics follow the temporal terahertz field oscillation, are tightly locked to the terahertz phase and are induced in the absence of resonant excitations and energy deposition. The magnetic response occurs on the timescale of the stimulus and is thus two orders of magnitude faster than the Larmor precession response. The experimental results are excellently reproduced by the Landau–Lifshift–Gilbert semi-empirical model, indicating its applicability to ultrafast magnetization dynamics and also demonstrating the marginal effect of the co-propagating terahertz electric field. This novel phenomenon of phase-locked control of magnetization with a strong terahertz field suggests new opportunities for ultrafast data storage.