Controllable Experimental Technique and Efficient Electromagnetic Modeling Method of Femtosecond Electron Emission from Nano Emitters

<title>Abstract</title> <p>Ultrafast electron emission from cold cathodes has long attracted interest. Femtosecond-laser-excited ultrafast electron emission from nano emitters is critical for new terahertz radiation sources, petahertz vacuum nanoelectronic devices and ultrafast electron imaging systems, owing to its ultrahigh temporal resolution. Developing methods for characterizing the temporal properties of femtosecond electron pulses is a top priority. However, such characterization often faces the challenge of incomplete information acquisition, making it difficult to directly analyze key parameters such as transient photocurrent distribution. In light of this, the simultaneous establishment of a characterization method and a quantitative electromagnetic modeling method to enable highthroughput, rapid prediction of key parameters is of significant importance. In this work, to suppress the initial time delay and energy dispersion inherent in conventional mechanisms, ultrafast electron emission experiments are conducted based on femtosecond laser-driven transient optical field emission from large-area carbon nanotube emitters. Relying on this, the temporal properties of electron pulses are quantitatively characterized using the electron autocorrelation method with a developed femtosecond-level temporal resolution directly at the detection position. Additionally, an innovative full-wave electromagnetic modeling method is constructed by combining the augmented electric-field integral equation (AEFIE) with the Drude-Lorentz model to serve as a physical inversion benchmark for the experimentally inaccessible time-domain information. The results reveal that the width of electron pulses is smaller than that of laser pulses, and that the emission current follows the shape of a femtosecond laser pulse. Furthermore, modeling predicts that increasing the number of carbon nanotube emitters effectively decreases the electron pulse width. Overall, the combined experimental and modeling method connects electron-pulse reconstruction with terahertz-radiation validation, providing guidance for the design of ultrafast electron sources.</p>