Acceleration element for femtosecond electron pulse compression

Abstract

An acceleration element is proposed for compressing the electron pulse duration in a femtosecond photoelectron gun. The element is a compact metal cavity with curved-shaped walls. An external voltage is applied to the cavity where a special electric field forms in such a way that the slow electrons in the electron pulse front are accelerated more than the fast electrons, and consequently the electron pulse duration will be compressed. The distribution of the electric field inside the acceleration cavity is analyzed for the geometry of the cavity. The electron dynamics in this acceleration cavity is also investigated numerically. Numerical results show that the electron pulse front and pulse duration can be improved by compensating for the effects of space charge and the initial energy spread of photoelectrons with a Lambertian angular distribution. Depending on the design parameters and the shape of the electron pulse, for a femtosecond electron gun with an electron energy of 30 keV, 10(3) electrons per pulse, and an electron drift length of 40 cm, the electron pulse duration can be reduced from 550 to 200 fs when using a compensating cavity with an average radius of 1.7 and 5.6 cm in length. Electron pulses shorter than 200 fs can be achieved if the length of the drift region is reduced.

Hybrid dc–ac electron gun for fs-electron pulse generation

“…Equation (12) shows that the pulse duration will change asymmetrically with the phase error ϕ. For a negative phase error ϕ the denominator decreases, but cos ϕ also decreases.…”

“…Slicing an ultrashort electron pulse out of a longer one by femtosecond electron pulse gating with surface plasmons [9] or by ponderomotive deflection [10] has also been proposed. Another suggestion is sub-fs pulse generation by electron bunching using a 'temporal lens' [11] or a cavity with a curve-shaped wall [12]. More recently, electron pulses emitted from a sharp tungsten tip by means of a few-cycle laser pulse have been observed and simulations indicate that single electron pulses of sub-fs duration may be generated in this way [13].…”

Double-mode electrostatic dispersing prism for electron pulse time-domain compression

“…More has been done theoretically and experimentally to obtain femtosecond or even attosecond electron pulse [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The techniques available now can be classified into two types.…”

“…The techniques available now can be classified into two types. For the first type the electron pulse duration is modulated with spatially nonhomogeneous stationary electromagnetic field provided by specifically devised electron-optical system [8,9,21,22], such as introducing the accelerating element in the traditional photoelectron gun [9]. In contrast to the first type, the electronpulse-duration modulation is accomplished by non-stationary electromagnetic field for the second one [10][11][12][13][14][15][16][17][18][19][20][23][24][25], in which electrons in different portion are subject to differential velocity (or energy) modulation.…”

Breaking resolution limits in ultrafast electron diffraction and microscopy

“…In contrast, a single shot with a large number of electrons experiences major space-charge effects due to Coulomb repulsion, which results in temporal and energy spread during propagation. To compensate for this effect, a proposal was made to recompress the pulses after broadening by space-charge repulsion (18). Here, we present an approach that is based on tilting the electron packets themselves to allow for self-compression of the pulse.…”