Novel ultrafast laser ablation by bibursts in the MHz and GHz pulse repetition rates

利用机器学习开展大科学装置环境下的超快科学研究：机遇与挑战

Harnessing Machine Learning for Ultrafast Science in Facility Settings: Opportunities and Challenges

该研究探讨机器学习作为下一代超快科学装置使能层的机遇与挑战，提出含多环节的装置级数字架构，结合ELI三大设施案例，论证其可支持实时诊断等多种工作流程。

Single-frame characterization of ultrafast pulses with spatiotemporal orbital angular momentum

Light carrying spatiotemporal orbital angular momentum (ST-OAM) makes possible new types of optical vortices arising from transverse OAM. ST-OAM pulses exhibit novel properties during propagation, transmission, refraction, diffraction, and nonlinear conversion, attracting growing experimental and theoretical interest and studies. However, one major challenge is the lack of a simple and straightforward method for characterizing ultrafast ST-OAM pulses. Using spatially resolved spectral interferometry, we demonstrate a simple, stationary, single-frame method to quantitatively characterize ultras…

High spatial coherence in multiphoton-photoemitted electron beams

Nanometer-sharp metallic tips are known to be excellent electron emitters. They are used in highest-resolution electron microscopes in cold field emission mode to generate the most coherent electron beam in continuous-wave operation. For time-resolved operation, sharp metal needle tips have recently been triggered with femtosecond laser pulses. We show here that electrons emitted with near-infrared femtosecond laser pulses at laser oscillator repetition rates show the same spatial coherence properties as electrons in cold field emission mode in cw operation. From electron interference fringes,…

High quality ultrafast transmission electron microscopy using resonant microwave cavities

Ultrashort, low-emittance electron pulses can be created at a high repetition rate by using a TM$_{110}$ deflection cavity to sweep a continuous beam across an aperture. These pulses can be used for time-resolved electron microscopy with atomic spatial and temporal resolution at relatively large average currents. In order to demonstrate this, a cavity has been inserted in a transmission electron microscope, and picosecond pulses have been created. No significant increase of either emittance or energy spread has been measured for these pulses. At a peak current of $814\pm2$ pA, the root-mean-sq…

Ultrafast-laser-absorption spectroscopy for single-shot, mid-infrared measurements of temperature, CO, and CH$_4$ in flames

This manuscript describes the development of an ultrafast (i.e.,femtosecond), mid-infrared, laser-absorption diagnostic and its initial application to measuring temperature, CO, and CH$_4$ in flames. The diagnostic employs a Ti:Sapphire oscillator emitting 55-fs pulses near 800 nm which were amplified and converted into the mid-infrared (mid-IR) though optical parametric amplification (OPA) at a repetition rate of 5 kHz. The pulses were directed through the test gas and into a high-speed mid-infrared spectrograph to image spectra across a $\approx$30 nm bandwidth with a spectral resolution of …

Efficient Terahertz Generation Using Fe/Pt Spintronic Emitters Pumped at Different Wavelengths

Recent studies in spintronics have highlighted ultrathin magnetic metallic multilayers as a novel and very promising class of broadband terahertz radiation sources. Such spintronic multilayers consist of ferromagnetic (FM) and non-magnetic (NM) thin films. When triggered by ultrafast laser pulses, they generate pulsed THz radiation due to the inverse spin-Hall effect, a mechanism that converts optically driven spin currents from the magnetized FM layer into transient transverse charge currents in the NM layer, resulting in THz emission. As THz emitters, FM/NM multilayers have been intensively …