###### Abstract  
Femtosecond laser filament-generated plasma can generate electromagnetic pulses (EMPs). These pulses may reduce the instrument's precision, and, hence, influence the accuracy of the experimental results. They may even cause widespread disruption by disabling of the electronic control systems or distribution networks of power plants. This study investigated the characteristics of EMPs generated from the interaction of filament-generated plasmas with a solid target in air. In this study, ultrafast laser filamentation was used to produce plasma, which was focused on a 3 mm-thick aluminum (Al) alloy target for interaction, and the spatial distribution and main contributors of the EMPs were systematically and extensively studied. The results showed that the EMPs generated from ultrafast laser filament interaction with the Al alloy target had the following characteristics: the EMP energy generated from laser filament interaction with solid targets is tens of times higher than that generated only from the femtosecond laser filament; the maximum EMP signals appeared at a 20\({}^{\circ}\)-80\({}^{\circ}\)detection angle. The relationship between the energy of EMPs and the width and energy of the laser pulses is presented and discussed. These findings are beneficial for gaining insight into the EMP generation mechanism, spatial distribution, and transmission, and for providing more information for the design of EMPs' shielding. f 6 May 2022  
Accepted: 13 June 2022  
generated by sub-ps laser-solid target interactions are stronger than those generated by nanosecond (ns) laser-solid target interaction. Moreover, it was verified that the GHz EMP source is generated due to the current from the bolster structure to the target. Furthermore, charge separation and target polarization under powerful laser pulse radiation cause the target to be charged by rapid charge accumulation [10]. Therefore, EMPs can be mitigated by controlling the geometrical and electrical characteristics of the target [11; 12]. To gain a better understanding of the characteristics and mitigation methods of EMP, substantial efforts have been made in large laser facilities. To date, experimental observations of radio-frequency and microwave radiation from laser-plasma interactions are usually associated with nanosecond to femtosecond pulses directly irradiating solid targets [2; 5; 13; 14; 15]. EMPs usually arise from two mechanisms associated with terawatt- to petawatt-level laser-matter interactions: ionization, via propagation in air, and plasma generation, which is associated with laser-excited solid materials. With the rapid development of femtosecond lasers, the mechanism and characteristics of low-frequency and relatively low-energy EMP produced by femtosecond laser filaments in air have gained attention from researchers [16; 17; 18; 19; 20; 21]. When an ultrashort laser pulse above a critical power of several GW is focused onto a spot of tens of micrometers radius, the intensity of the core reaching \(10^{13}\)-\(10^{14}\) W/cm\({}^{2}\)[22] is sufficient to ionize the molecules or atoms of the atmosphere [23], forming a plasma [24]. Then, owing to the Kerr effect, a dynamic balance is built between laser beam self-focus and plasma defocus. Finally, the femtosecond laser in the air forms a long-distance plasma channel, namely a femtosecond laser filament. Currently, femtosecond laser filament technology is widely used in astronomy, meteorology, information, medical treatment, industry, and other fields, including artificial rainfall and snow, laser lightning induction, and air waveguide [25; 26; 27; 28]. An extension of laser-filament-driven sources of low-frequency radiation below the THz borderline would help avoid strong atmospheric absorption bands that limit long-distance transmission and remote-sensing applications of THz radiation, and would help integrate cutting-edge tools of ultrafast optics and microwave photonics. Research on EMPs mitigation has been mainly focused on high-energy area EMPs in vacuum.