Ultrafast laser pulses provide unique tools to manipulate magnetization dynamics at femtosecond timescales, where the interaction of the electric field usually dominates over the magnetic field. Recent proposals using structured laser beams have demonstrated the possibility to produce regions where intense oscillating magnetic fields are isolated from the electric field. In these conditions, we show that technologically feasible tesla-scale circularly polarized high-frequency magnetic fields induce purely precessional nonlinear magnetization dynamics. This fundamental result not only opens an avenue in the study of laser-induced ultrafast magnetization dynamics, but also sustains technological implications as a route to promote all-optical non-thermal magnetization dynamics both at shorter timescales – towards the sub-femtosecond regime – and at THz frequencies.chiral behavior nonlinear dynamics ultrafast dynamics
High Power Laser Science and Engineering
2023, 11(6): 06000e82
Nonlinear compression has become an obligatory technique along with the development of ultrafast lasers in generating ultrashort pulses with narrow pulse widths and high peak power. In particular, techniques of nonlinear compression have experienced a rapid progress as ytterbium (Yb)-doped lasers with pulse widths in the range from hundreds of femtoseconds to a few picoseconds have become mainstream laser tools for both scientific and industrial applications. Here, we report a simple and stable nonlinear pulse compression technique with high efficiency through cascaded filamentation in air followed by dispersion compensation. Pulses at a center wavelength of 1040 nm with millijoule pulse energy and 160 fs pulse width from a high-power Yb:CaAlGdO4 regenerative amplifier are compressed to 32 fs, with only 2.4% loss from the filamentation process. The compressed pulse has a stable output power with a root-mean-square variation of 0.2% over 1 hour.femtosecond pulse filamentation nonlinear compression
High Power Laser Science and Engineering
2023, 11(6): 06000e84
The spatial distribution of beams with orbital angular momentum in the far field is known to be extremely sensitive to angular aberrations, such as astigmatism, coma and trefoil. This poses a challenge for conventional beam optimization strategies when a homogeneous ring intensity is required for an application. We developed a novel approach for estimating the Zernike coefficients of low-order angular aberrations in the near field based solely on the analysis of the ring deformations in the far field. A fast, iterative reconstruction of the focal ring recreates the deformations and provides insight into the wavefront deformations in the near field without relying on conventional phase retrieval approaches. The output of our algorithm can be used to optimize the focal ring, as demonstrated experimentally at the 100 TW beamline at the Extreme Light Infrastructure - Nuclear Physics facility.beam quality far field orbital angular momentum ring intensity phase retrieval wavefront
High Power Laser Science and Engineering
2023, 11(6): 06000e86
A silicon-based digitally tunable positive/negative dispersion controller (DC) is proposed and realized for the first time using the cascaded bidirectional chirped multimode waveguide gratings (CMWGs), achieving positive and negative dispersion by switching the light propagation direction. A 1 × 2 Mach–Zehnder switch (MZS) and a 2 × 1 MZS are placed before and after to route the light path for realizing positive/negative switching. The device has Q stages of identical bidirectional CMWGs with a binary sequence. Thus the digital tuning is convenient and scalable, and the total dispersion accumulated by all the stages can be tuned digitally from - ( 2Q - 1 ) D0 to ( 2Q - 1 ) D0 with a step of D0 by controlling the switching states of all 2 × 2 MZSs, where D0 is the dispersion provided by a single bidirectional CMWG unit. Finally, a digitally tunable positive/negative DC with Q = 4 is designed and fabricated. These CMWGs are designed with a 4-mm-long grating section, enabling the dispersion D0 of about 4.16 ps / nm in a 20-nm-wide bandwidth. The dispersion is tuned from -61.53 to 63.77 ps / nm by switching all MZSs appropriately, and the corresponding group delay is varied from -1021 to 1037 ps.silicon photonics dispersion tuning digital tuning multimode waveguide grating
2023, 5(6): 066005
The 2023 Nobel Prize in Physics spotlights the techniques to generate attosecond light pulses. The generation of attosecond pulses heralds a new era in understanding electron dynamics. This perspective traces the evolution of ultrafast science, from early microwave electronics to the recent breakthroughs in attosecond pulse generation and measurement. Key milestones, such as high harmonic generation, the RABBITT method, attosecond streaking camera, etc, illuminate our journey toward capturing the transient electron motions in atoms. Recent discoveries, including zeptosecond delays in H2 single-photon double ionization and the potential of attosecond “electron” pulses despite challenges, etc., hint at an exciting future for ultrafast studies.
2023, 3(1): 0049
In the last few decades, there have been several advances in ultrafast imaging of light propagation with light-in-flight recording by holography (LIF holography), which can capture light propagation as a motion picture with a single shot in principle. Here, we review the recent advances in LIF holography by considering the perspectives of various development of functional imaging techniques and evaluation of LIF holography with numerical simulation methods. The methods for recording multiple motion pictures such as a space-division multiplexing, a pixel-by-pixel-based space-division multiplexing, and an angular multiplexing technique are added extend the capability of LIF holography. The numerical simulation models used for investigating the image characteristics of LIF hologram are discussed. Finally, a summary and conclusion of recent advances in LIF holography is presented.
2023, 3(1): 0043
The surface/interface species in perovskite oxides play essential roles in many novel emergent physical phenomena and chemical processes. With low eigen-energies in the terahertz region, such species at buried interfaces remain poorly understood due to the lack of feasible surface-specific spectroscopic probes to resolve the resonances. Here, we show that polarized phonons and two-dimensional electron gas at the interface can be characterized using surface-specific nonlinear optical spectroscopy in the terahertz range. This technique uses intra-pulse difference frequency mixing process, which is allowed only at the surface/interface of a centrosymmetric medium. Submonolayer sensitivity can be achieved using the state-of-the-art detection scheme for the terahertz emission from the surface/interface. Through symmetry analysis and proper polarization selection, background-free Drude-like nonlinear response from the two-dimensional electron gas emerging at the LaAlO3/SrTiO3 or Al2O3/SrTiO3 interface was successfully observed. The surface/interface potential, which is a key parameter for SrTiO3-based interface superconductivity and photocatalysis, can now be determined optically in a nonvacuum environment via quantitative analysis on the phonon spectrum that was polarized by the surface field in the interfacial region. The interfacial species with resonant frequencies in the THz region revealed by our method provide more insights into the understanding of physical properties of complex oxides.
2023, 3(1): 0042
Amplitude mode is collective excitation emerging from frozen lattice distortions below the charge-density-wave (CDW) transition temperature TCDW and relates to the order parameter. Generally, the amplitude mode is non-polar (symmetry-even) and does not interact with incoming infrared photons. However, if the amplitude mode is polar (symmetry-odd), it can potentially couple with incoming photons, thus forming a coupled phonon–polariton quasiparticle that can travel with light-like speed beyond the optically excited region. Here, we present the amplitude mode dynamics far beyond the optically excited depth of ∼150 nm in the CDW phase of ∼10-μm-thick single-crystal EuTe4 using time-resolved x-ray diffraction. The observed oscillations of the CDW peak, triggered by photoexcitation, occur at the amplitude mode frequency ωAM. However, the underdamped oscillations and their propagation beyond the optically excited depth are at odds with the observation of the overdamped nature of the amplitude mode measured using meV-resolution inelastic x-ray scattering and polarized Raman scattering. The ωAM is found to decrease with increasing fluence owing to a rise in the sample temperature, which is independently confirmed using polarized Raman scattering and ab-initio molecular dynamics simulations. We rationalize the above observations by explicitly calculating two coupled quasiparticles—phonon–polariton and exciton–polariton. Our data and simulations cannot conclusively confirm or rule out the one but point toward the likely origin from propagating phonon–polariton. The observed non-local behavior of amplitude mode thus provides an opportunity to engineer material properties at a substantially faster time scale with optical pulses.
2023, 3(1): 0041
Nonadiabatic dynamics around an avoided crossing or a conical intersection play a crucial role in the photoinduced processes of most polyatomic molecules. The present work shows that the topological phase in conical intersection makes the behavior of pump-probe high-order harmonic signals different from the case of avoided crossing. The coherence built up when the system crosses the avoided crossing will lead to the oscillatory behavior of the spectrum, while the geometric phase erodes these oscillations in the case of conical intersection. Additionally, the dynamical blueshift and the splitting of the time-resolved spectrum allow capturing the snapshot dynamics with the sub-femtosecond resolution.
2023, 3(1): 0040
One of the main constraints for reducing the temporal duration of attosecond pulses is the attochirp inherent to the process of high-order harmonic generation (HHG). Though the attochirp can be compensated in the extreme-ultraviolet using dispersive materials, this is unfeasible toward x-rays, where the shortest attosecond or even sub-attosecond pulses could be obtained. We theoretically demonstrate that HHG driven by a circularly polarized infrared pulse while assisted by an strong oscillating ultrafast intense magnetic field enables the generation of few-cycle Fourier-limited few attosecond pulses. In such a novel scenario, the magnetic field transversally confines the ionized electron during the HHG process, analogously to a nanowire trapping. Once the electron is ionized, the transverse electron dynamics is excited by the magnetic field, acting as a high-energy reservoir to be released in the form of phase-locked spectrally wide high-frequency harmonic radiation during the electron recollision with the parent ion. In addition, the transverse breathing dynamics of the electron wavepacket, introduced by the magnetic trapping, strongly modulates the recollision efficiency of the electronic trajectories, thus the attosecond pulse emissions. The aftermath is the possibility of producing high-frequency (hundreds of eV) attosecond isolated few-cycle pulses, almost Fourier limited. The isolated intense magnetic fields considered in our simulations, of tens of kT, can be produced in finite spatial volumes considering structured beams or stationary configurations of counter-propagating state-of-the-art multi-terawatt/petawatt lasers.
2023, 3(1): 0036