Attosecond electron microscopy and diffraction.

Advances in attosecond spectroscopy have enabled tracing and controlling the electron motion dynamics in matter, although they have yielded insufficient information about the electron dynamic in the space domain. Hence, ultrafast electron and x-ray imaging tools have been developed to image the ultrafast dynamics of matter in real time and space. The cutting-edge temporal resolution of these imaging tools is on the order of a few tens to a hundred femtoseconds, limiting imaging to the atomic dynamics and leaving electron motion imaging out of reach. Here, we obtained the attosecond temporal resolution in the transmission electron microscope, which we coined "attomicroscopy." We demonstrated this resolution by the attosecond diffraction measurements of the field-driven electron dynamics in graphene. This attosecond imaging tool would provide more insights into electron motion and directly connect it to the structural dynamics of matter in real-time and space domains, opening the door for long-anticipated real-life attosecond science applications in quantum physics, chemistry, and biology.

Ultrafast optical switching and data encoding on synthesized light fields.

Modern electronics are founded on switching the electrical signal by radio frequency electromagnetic fields on the nanosecond time scale, limiting the information processing to the gigahertz speed. Recently, optical switches have been demonstrated using terahertz and ultrafast laser pulses to control the electrical signal and enhance the switching speed to the picosecond and a few hundred femtoseconds time scale. Here, we exploit the reflectivity modulation of the fused silica dielectric system in a strong light field to demonstrate the optical switching (ON/OFF) with attosecond time resolution. Moreover, we present the capability of controlling the optical switching signal with complex synthesized fields of ultrashort laser pulses for data binary encoding. This work paves the way for establishing optical switches and light-based electronics with petahertz speeds, several orders of magnitude faster than the current semiconductor-based electronics, opening a new realm in information technology, optical communications, and photonic processor technologies.

Attosecond electronic delay response in dielectric materials.

The advancement in the attosecond field and the generation of XUV attosecond pulses has enabled the study of electron dynamics in the solid-state by high harmonic generation spectroscopy. Here, we introduce new all-optical attosecond metrology to study the light-field induced electron dynamics in dielectric systems. This new methodology is based on the phase transition of a dielectric material due to its interaction with a strong light field. Hence, the charge carriers undergo an inter- and intraband transition, causing a modification in the electronic structure, dielectric constant, and optical properties of the dielectric system. Consequently, the dielectric material experiences an adiabatic semi-metal phase transition due to the strong polarizability. Therefore, the reflectivity of the dielectric system changes, following the shape of the pump field. Accordingly, the time-resolved reflectivity change measurement provides direct access to the phase transition and the related electronic dynamics of the system in real-time. In the reported experiment, a strong light field (pump pulse) induces the phase transition and modifies the fused silica sample's reflectivity, which is probed by another weak light field (probe pulse). The reflected probe beam spectrum is acquired as a function of the time delay between the pump and probe pulses. This measurement shows that the real-time phase transition dynamic (and reflectivity change) follows the pump field shape. Moreover, the reflectivity measurements have been recorded at different pump field strengths performed under the same conditions. The reflectivity trace shows a retardation phase delay at a higher driver field strength. The delay response-retrieved from the recorded reflectivity traces-is in the order of a few hundred attoseconds. In addition, the results show that the delay response monotonically increases as the trigger field escalates. Furthermore, the reflectivity measurements have been acquired for another dielectric system (CaF2). The electronic delay response shows the same linear behavior increase as that of the SiO2 system. This work establishes a universal new attosecond metrology for measuring the electron dynamics and delay response in different materials.

A compact large-format streak tube for imaging lidar.

The streak tubes with a large effective photocathode area, large effective phosphor screen area, and high photocathode radiant sensitivity are essential for improving the field of view, depth of field, and detectable range of the multiple-slit streak tube imaging lidar. In this paper, a high spatial resolution, large photocathode area, and compact meshless streak tube with a spherically curved cathode and screen is designed and tested. Its spatial resolution reaches 20 lp/mm over the entire Φ28 mm photocathode working area, and the simulated physical temporal resolution is better than 30 ps. The temporal distortion in our large-format streak tube, which is shown to be a non-negligible factor, has a minimum value as the radius of curvature of the photocathode varies. Furthermore, the photocathode radiant sensitivity and radiant power gain reach 41 mA/W and 18.4 at the wavelength of 550 nm, respectively. Most importantly, the external dimensions of our streak tube are no more than Φ60 mm × 110 mm.