Dual mode microwave deflection cavities for ultrafast electron microscopy

Abstract

This paper presents the experimental realization of an ultrafast electron microscope operating at a repetition rate of 75 MHz based on a single compact resonant microwave cavity operating in dual mode. This elliptical cavity supports two orthogonal TM${}_{110}$ modes with different resonance frequencies that are driven independently. The microwave signals used to drive the two cavity modes are generated from higher harmonics of the same Ti:Sapphire laser oscillator. Therefore the modes are accurately phase-locked, resulting in periodic transverse deflection of electrons described by a Lissajous pattern. By sending the periodically deflected beam through an aperture, ultrashort electron pulses are created at a repetition rate of 75 MHz. Electron pulses with $\tau =(750\pm 10)$ fs pulse duration are created with only $(2.4\pm 0.1)$ W of microwave input power; with normalized rms emittances of ${\epsilon }_{n,x}=(2.1\pm 0.2)$ pm rad and ${\epsilon }_{n,y}=(1.3\pm 0.2)$ pm rad for a peak current of $I_p=(0.4\pm 0.1)$ nA. This corresponds to an rms normalized peak brightness of $B_{np,\text{rms}}=(7\pm 1)\times 10^6$ A/m${}^2$ sr V, equal to previous measurements for the continuous beam. In addition, the FWHM energy spread of $\Delta U=(0.90\pm 0.05)$ eV is also unaffected by the dual mode cavity. This allows for ultrafast pump-probe experiments at the same spatial resolution of the original TEM in which a 75 MHz Ti:Sapphire oscillator can be used for exciting the sample. Moreover, the dual mode cavity can be used as a streak camera or time-of-flight EELS detector with a dynamic range $>10^4$.

References in corpus (6)

• Ultrafast transmission electron microscopy using a laser-driven field emitter: femtosecond resolution with a high coherence electron beam
• Compression of sub-relativistic space-charge-dominated electron bunches for single-shot femtosecond electron diffraction
• Ramsey-type phase control of free electron beams
• Highly coherent electron beam from a laser-triggered tungsten needle tip
• High quality ultrafast transmission electron microscopy using resonant microwave cavities
• Theory and particle tracking simulations of a resonant radiofrequency deflection cavity in TM${}_{110}$ mode for ultrafast electron microscopy

Cited by in corpus (5)

• Control of quantum electrodynamical processes by shaping electron wavepackets
• Free Electrons Can Induce Entanglement Between Photons
• Design and characterization of dielectric filled TM${}_{110}$ microwave cavities for ultrafast electron microscopy
• Nanosecond Electron Holography by Interference Gating
• Ultrafast Electron Diffraction: Visualizing Dynamic States of Matter