Isolated attosecond pulses (IAPs) are generated via applying amplitude gating on high-order harmonic generation driven by carrier-envelope phase stabilized 5.2 fs pulses with 0.5 mJ pulse energy at 770 nm central wavelength at the Synergetic Extreme Condition User Facility. A continuum ranging from 70 to 100 eV that supports sub-100-attosecond pulse is extracted by Zr foil and Mo/Si multilayer mirror. We demonstrate the characterization of the IAP. The retrieved pulse duration is 86 attoseconds. The developed attosecond laser beamline with repetition rate up to 10 kHz is available for users to conduct attosecond photoelectron spectroscopy researches with a capability of coincidence measurement.

A cylindrical Öffner stretcher based on ternary reflector (COSTER) is proposed and analyzed. Compared with the traditional Öffner stretcher, the COSTER has no off-axis aberration in the multipass configuration, and the output laser of COSTER has lower spectral phase noise and higher temporal contrast in the far field. The COSTER is quite suitable to be used in multi-petawatt laser facilities, and it might be the preferred stretcher configuration for ultrafast and ultra-intense lasers.

The temporal evolutions of electron density and plasma diameter of 1 kHz femtosecond laser filament in air are experimentally investigated by utilizing a pump-probe longitudinal diffraction method. A model based on scalar diffraction theory is proposed to extract the spatial phase shift of the probe pulse from the diffraction patterns by the laser air plasma channel. The hydrodynamic effect on plasma evolution at 1 kHz filament is included and analyzed. The measured initial peak electron density of ∼1018cm-3 in our experimental conditions decays rapidly by nearly two orders of magnitude within 200 ps. Moreover, the plasma channel size rises from 90 µm to 120 µm as the delay time increases. The experimental observation is in agreement with numerical simulation results by solving the rate equations of the charged particles.

Spintronic thin films are considered as one of the promising terahertz (THz) source candidates, owing to their high performance and low cost. Much effort has been made to achieve spintronic THz sources with broadband and high conversion efficiency. However, the development of spintronic THz emitters with good compatibility, low cost, and miniaturized technology still faces many challenges. Therefore, it is urgent to extend commercial and portable spintronic THz emitters to satisfy many practical applications. Herein, we design a new generation of spintronic THz emitters composed of an alternating electromagnet and a miniaturized electronic controller. Not only can this new type of spintronic THz emitter largely simplify the ancillary equipment for spintronic sources, it also has a twice larger THz signal compared to the traditional THz time-domain spectroscopy systems with a mechanical chopper. Experimental results and theoretical calculations for electromagnetic coils show that our design can stably generate THz signals that are independent of the frequency and magnetic field of alternating signals. As the spin thin film is optimized, a magnetic field as low as 75 G satisfies the requirement for high performance THz emission. Hence, not only is the efficiency of the pump power enhanced, but also the driving current in the electromagnet is decreased. We believe that it has a wide range of applications and profound implications in THz technology based on spintronic emitters in the future.

Electric fields modify the optical properties of nematic liquid crystals (NLCs) by changing the nematic molecular orientation or order parameters, which enables electro-optic applications of NLCs. However, the field-induced optic change is undesirable in some cases. Here, we experimentally demonstrate that polymer stabilization weakens the birefringence change of NLCs caused by the nanosecond electrically modified order parameter effect. The birefringence change is reduced by 65% in the NLC doped with 25% reactive monomer, which is polymerized close to the nematic-to-isotropic phase transition. This technique could be used in liquid crystal devices where the birefringence change is unfavored.

High-harmonic generation in metasurfaces, driven by strong laser fields, has been widely studied. Compared to plasma, all-dielectric nanoscale metasurfaces possess larger nonlinearity response and higher damage threshold. Additionally, it can strongly localize the driven field, greatly enhancing its peak amplitude. In this work, we adopt a Fano resonant micro-nano structure with transmission peaks at different wavelengths and explore its nonlinear response by both single and two-color pump fields. Compared to the high-order harmonics induced by the first resonant wavelength, the intensity of the high-harmonic radiation results is enhanced by one order of magnitude, when the metasurface is driven by various resonant and non-resonant wavelength combinations of a two-color field.

Laser polarization and its intensity inside a filament core play an important role in filament-based applications. However, polarization dependent clamping intensity inside filaments has been overlooked to interpret the polarization-related filamentation phenomena. Here, we report on experimental and numerical investigations of polarization dependent clamping intensity inside a femtosecond filament in air. By adjusting the initial polarization from linear to circular, the clamping intensity is increased by 1.36 times when using a 30 cm focal length lens for filamentation. The results indicate that clamping intensity inside the filament is sensitive to laser polarization, which has to be considered to fully understand polarization-related phenomena.

We calculate the time-energy distribution (TED) and ionization time distribution (ITD) of photoelectrons emitted by a double-extreme-ultraviolet (XUV) pulse and a two-color XUV-IR pulse using the Wigner distribution-like function based on the strong field approximation. For a double-XUV pulse, besides two identical broad distributions generated by two XUV pulses, many interference fringes resulting from the interference between electrons generated, respectively, by two pulses appear in the TED. After adding an IR field, the TED intuitively exhibits the effect of the IR field on the electron dynamics. The ITDs during two XUV pulses are no longer the same and show the different changes for the different two-color fields, the origin of which is attributed to the change of the electric field induced by the IR field. Our analysis shows that the emission time of electrons ionized during two XUV pulses mainly depends on the electric field of the combined XUV pulse and IR pulse.

We demonstrate nonlinear pulse compression of an 8 kHz Nd:YVO4 picosecond laser using the multi-pass-cell (MPC) technique with fused silica as the nonlinear medium. The pulse duration is compressed from 12.5 ps to 601 fs, corresponding to a pulse shortening factor of 20.8. The output pulse energy is 154 μJ with an efficiency of 74.5%. To the best of our knowledge, this is the highest pulse compression ratio achieved in a single-stage MPC with bulk material as the nonlinear medium. The laser power stability and the beam quality (M2) before and after the MPC are also experimentally studied. Both the laser power stability and the beam quality are barely deteriorated by the MPC device.

Ball lightning is widely concerning because it is hard to detect, predict, and reproduce. The dependences of electromagnetic (EM) solitons, which are considered expectant ball lightning, forming at the wavelength of the incident light are investigated with two-dimensional particle-in-cell simulations. It shows that both the long wavelength microwave and the short wavelength laser are not suitable for producing the observed ball-lightning-like EM solitons. A strong field terahertz wave is proposed to inject and generate EM solitons. This paper can provide some references for researchers studying ball lightning.