ABSTRACT
The microscopic origin of ultrafast modification of the ratio between the symmetric (J) and antisymmetric (D) exchange interaction in antiferromagnetic iron oxides is revealed, using femtosecond laser excitation as a pump and terahertz emission spectroscopy as a probe. By tuning the photon energy of the laser pump pulse we show that the effect of light on the D/J ratio in two archetypical iron oxides FeBO_{3} and ErFeO_{3} is maximized when the photon energy is in resonance with a spin and parity forbidden d-d transition between the crystal-field split states of Fe^{3+} ions. The experimental findings are supported by a multielectron model, which accounts for the resonant absorption of photons by Fe^{3+} ions. Our results reveal the importance of the parity and spin-change forbidden, and therefore often underestimated, d-d transitions in ultrafast optical control of magnetism.
ABSTRACT
We show that femtosecond laser pulse excitation of the orthoferrite ErFeO_{3} triggers pico- and subpicosecond dynamics of magnetic and electric dipoles associated with the low energy electronic states of the Er^{3+} ions. These dynamics are readily revealed by using polarization sensitive terahertz emission spectroscopy. It is shown that by changing the polarization of the femtosecond laser pulse one can excite either electric dipole-active or magnetic dipole-active transitions between the Kramers doublets of the ^{4}I_{15/2} ground state of the Er^{3+} (4f^{11}) ions. These observations serve as a proof of principle of polarization-selective control of both electric and magnetic degrees of freedom at terahertz frequencies, opening up new vistas for optical manipulation of magnetoelectric materials.
ABSTRACT
The idea to use not only the charge but also the spin of electrons in the operation of electronic devices has led to the development of spintronics, causing a revolution in how information is stored and processed. A novel advancement would be to develop ultrafast spintronics using femtosecond laser pulses. Employing terahertz (10(12)â Hz) emission spectroscopy and exploiting the spin-orbit interaction, we demonstrate the optical generation of electric photocurrents in metallic ferromagnetic heterostructures at the femtosecond timescale. The direction of the photocurrent is controlled by the helicity of the circularly polarized light. These results open up new opportunities for realizing spintronics in the unprecedented terahertz regime and provide new insights in all-optical control of magnetism.
ABSTRACT
We study the focusing of light through random photonic materials using wavefront shaping. We explore a novel approach namely binary amplitude modulation. To this end, the light incident to a random photonic medium is spatially divided into a number of segments. We identify the segments that give rise to fields that are out of phase with the total field at the intended focus and assign these a zero amplitude, whereas the remaining segments maintain their original amplitude. Using 812 independently controlled segments of light, we find the intensity at the target to be 75±6 times enhanced over the average intensity behind the sample. We experimentally demonstrate focusing of light through random photonic media using both an amplitude only mode liquid crystal spatial light modulator and a MEMS-based spatial light modulator. Our use of Micro Electro-Mechanical System (MEMS)-based digital micromirror devices for the control of the incident light field opens an avenue to high speed implementations of wavefront shaping.
