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Coherent light-matter interactions mediated by opto-magnetic phenomena like the inverse Faraday effect (IFE) are expected to provide a non-thermal pathway for ultrafast manipulation of magnetism on timescales as short as the excitation pulse itself. As the IFE scales with the spin-orbit coupling strength of the involved electronic states, photo-exciting the strongly spin-orbit coupled core-level electrons in magnetic materials appears as an appealing method to transiently generate large opto-magnetic moments. Here, we investigate this scenario in a ferrimagnetic GdFeCo alloy by using intense and circularly polarized pulses of extreme ultraviolet radiation. Our results reveal ultrafast and strong helicity-dependent magnetic effects which are in line with the characteristic fingerprints of an IFE, corroborated by ab initio opto-magnetic IFE theory and atomistic spin dynamics simulations. Coherent light-matter interactions mediated by opto-magnetic phenomena like the inverse Faraday effect are expected to provide a non-thermal pathway for ultrafast manipulation of magnetism. The authors use intense and circularly polarized pulses of extreme ultraviolet radiation to induce particularly strong effects in a ferrimagnetic GdFeCo alloy. [ABSTRACT FROM AUTHOR]

Single-shot real-time femtophotography is indispensable for imaging ultrafast dynamics during their times of occurrence. Despite their advantages over conventional multi-shot approaches, existing techniques confront restricted imaging speed or degraded data quality by the deployed optoelectronic devices and face challenges in the application scope and acquisition accuracy. They are also hindered by the limitations in the acquirable information imposed by the sensing models. Here, we overcome these challenges by developing swept coded aperture real-time femtophotography (SCARF). This computational imaging modality enables all-optical ultrafast sweeping of a static coded aperture during the recording of an ultrafast event, bringing full-sequence encoding of up to 156.3 THz to every pixel on a CCD camera. We demonstrate SCARF's single-shot ultrafast imaging ability at tunable frame rates and spatial scales in both reflection and transmission modes. Using SCARF, we image ultrafast absorption in a semiconductor and ultrafast demagnetization of a metal alloy. The researchers showcase swept-coded aperture real-time femtophotography—an all-optical single-shot computational imaging modality at up to 156.3 trillion frames per second—video-records transient absorption in a semiconductor and ultrafast demagnetization of a metal alloy. [ABSTRACT FROM AUTHOR]

Instruments based on the magneto-optical Kerr effect are routinely used to probe surface magnetic properties. These tools rely on the characterization of the polarization state of reflected light from the sample to collect information on its magnetization. Here, we present a theoretical optimization of common setups based on the magneto-optical Kerr effect. A detection scheme based on a simple analyzer and photodetector and one made from a polarizing beam splitter and balanced photodetectors are considered. The effect of including a photoelastic modulator (PEM) and a lock-in amplifier to detect the signal at harmonics of the modulating frequency is studied. Jones formalism is used to derive general expressions that link the intensity of the measured signal to the magneto-optical Fresnel reflection coefficients for any orientation of the polarizing optical components. Optimal configurations are then defined as those that allow measuring the Kerr rotation and ellipticity while minimizing nonmagnetic contributions from the diagonal Fresnel coefficients in order to improve the signal-to-noise ratio (SNR). The expressions show that with the PEM, setups based on polarizing beam splitters inherently offer a twofold higher signal than commonly used analyzers, and the experimental results confirm that the SNR is improved by more than 150%. Furthermore, we find that while all proposed detection schemes measure Kerr effects, only those with polarizing beam splitters allow measuring the Kerr rotation directly when no modulator is included. This accommodates, for instance, time-resolved measurements at relatively low laser pulse repetition rates. Ultrafast demagnetization measurements are presented as an example of such applications. [ABSTRACT FROM AUTHOR]

Multidimensional solitary states (MDSS)—self-sustained wavepackets—have attracted renewed interest in many different fields of physics. They are of particular importance in nonlinear optics, especially for the nonlinear propagation of ultrashort pulses in multimode fibres, which contain rich spatiotemporal intermodal interactions and dynamics, albeit often in an unstable manner. Here, we report the observation of the formation of highly stable multidimensional solitary states in a molecular gas-filled large-core hollow-core fibre. We experimentally and numerically demonstrate the creation of MDSS by multimillijoule, subpicosecond near-infrared pulses and the underlying physics. We find that the MDSS have a broadband redshifted spectra with an uncommon negative quadratic spectral phase at the output of the hollow-core fibre, originating from Raman enhancement due to the strong intermodal nonlinear interactions. The spatial and temporal localization of MDSS enables the compression of the broadened pulses at the output to 10.8 fs by simple linear propagation in a piece of fused silica. The high spatiotemporal quality of MDSS is further verified by high-harmonic generation. Our results present new opportunities for studying multimodal spatiotemporal dynamics in the high-energy regime. This work also presents a route toward a new class of compact, tunable and high-energy spatiotemporally engineered coherent light sources based on picosecond ytterbium technology. The formation of multidimensional solitary states through the nonlinear propagation of high-energy pulses in a molecular gas-filled large-core hollow-core fibre is demonstrated, offering new opportunities for studying multimodal spatiotemporal dynamics in the high-energy regime. [ABSTRACT FROM AUTHOR]