Femtosecond diagnostics of ultrashort electron beam using a pinhole-based THz-driven deflector

Abstract

THz-driven resonant structures such as rectangular slits has been widely used for femtosecond temporal characterization of ultrashort electron beams produced in photocathode rf guns. In this work, we show that a simple non-resonant subwavelength pinhole perforated on a metal foil can also provide femtosecond temporal diagnostics to ultrashort electron beams. The streaking effect of the pinhole structure is dominated by the reflected THz field near the surface. A time resolution of 1.5 fs is achieved for a 3 MeV electron beam using a pinhole with diameter of 100 μm. A secondary beam, common in photocathode rf gun but hard to observe with conventional beam diagnostic methods, is also observed with the THz pinhole deflector. In addition to measuring the temporal information of the electron beam, we show that the pinhole may also be used to measure the properties of the THz pulse using the electron beam as the probe. We believe such simple and commercially available pinhole structure is a robust and viable method for femtosecond temporal diagnostics of ultrashort electron beams.