Direct Measurement of Sub-10 fs Relativistic Electron Beams with Ultralow Emittance

Abstract

Ultralow emittance (≤ 20 nm, normalized) electron beams with 10 5 electrons per bunch are obtained by tightly focusing an ultrafast (∼ 100 fs) laser pulse on the cathode of a 1.6 cell radiofrequency photoinjector. Taking advantage of the small initial longitudinal emittance, a downstream velocity bunching cavity is used to compress the beam to < 10 fs rms bunch length. The measurement is performed using a thick high voltage deflecting cavity which is shown to be well-suited to measure ultrashort durations of bunching beams, provided that the beam reaches a ballistic longitudinal focus at the cavity center.

Attosecond electron pulse trains and quantum state reconstruction in ultrafast transmission electron microscopy

“…Promising a further leap in temporal resolution, recent findings suggest that ultrafast electron diffraction and microscopy with optically phasecontrolled and sub-cycle, attosecond-structured wave functions may be feasible 8,[26][27][28][29][30] . Specifically, light-field control may translate the temporal resolution of ultrafast transmission electron microscopy (UTEM) 31,32 and electron diffraction (UED) 10,33 , currently at about 200 fs 34 and 20 fs 14,23 , respectively, to the range of attoseconds 26,27,35 . However, such future technologies call for means to both prepare and fully analyze the corresponding quantum states of free electrons.…”

“…Ultrafast imaging and spectroscopy with electrons and x-rays are the basis for an ongoing revolution in the understanding of dynamical processes in matter on atomic scales [10][11][12][13] . The underlying technology heavily rests on laser science for the generation and characterization of ever-shorter femtosecond electron 10,14 and xray [15][16][17] probe pulses, with examples in optical pulse compression 18 and streaking spectroscopy [19][20][21] . The temporal structuring of electron probe beams is facilitated by time-dependent fields in the radio-frequency [22][23][24] , terahertz 18,25 or optical domains.…”

Double-shot MeV electron diffraction and microscopy

“…Though the deflection cavity is capable of operating at a deflecting voltage of V d  = 500 keV and can have resolution in the sub-10 fs range, 12 considering the relatively long time separation of the two bunches, this case offers greater potential for image preservation in the streaking process. The angle between the two bunches after they pass through the deflector is given by $\Delta y\prime =S/L=\frac{e{V}_d}{m{c}^2\gamma }\omega \Delta t_{\mathit{s}\mathit{e}\mathit{p}},$where L is the distance from the deflector to the final screen, ω is the deflecting cavity angular frequency, and e / m is the charge to mass ratio of the electron.…”

“…This is the solution explored in this work. In particular, this case is modeled on the UCLA Pegasus beamline 12 where the addition of a linearizing cavity in the X-band (9.6 GHz) will provide a flat energy region of up to 20 ps. Nevertheless, the concept presented here can be easily generalizable to different setups.…”

Conceptual and Technical Design Aspects of Accelerators for External Injection in LWFA

“…Many different technologies have been proposed to reach the necessary resolution: an X-band RF deflector [90] succeeded in achieving a sub-fs resolution at SLAC. Recently at UCLA the first sub-10 fs high brightness beam has been characterized using the same method [91]. New designs for RF deflectors involving novel technologies, such as plasma Transverse Deflection Cavities [92] and THz streaking devices [93,94], have also been proposed and are currently in the development phase.…”