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Imaging single electrons to enable the generation of ultrashort beams for single-shot femtosecond relativistic electron diffraction
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Image of FIG. 1.
FIG. 1.

(Color online) Schematic of the phosphor screen, lens-coupling optics, and CCD camera configuration.

Image of FIG. 2.
FIG. 2.

(Color online) The SNR of a single MeV electron, SNR0, as a function of the EM gain level G EM for no binning and 2 × 2 pixels binning cases.

Image of FIG. 3.
FIG. 3.

(Color online) The ideal PSFs (left column) and their superpositions with the simulated camera readout noise (right column). The noise follows a normal distribution with an rms value as listed in Table I. (a) and (b) are for the no binning case, and (c) and (d) are for the 2 × 2 binning case.

Image of FIG. 4.
FIG. 4.

(Color online) (a) A typical image of field-emitted electrons in which each isolated spot is an electron. (b) The histogram of the total counts of each spot; 2.4 × 103 spots in 200 images are identified and counted.

Image of FIG. 5.
FIG. 5.

(Color online) Single-shot DPs of a 20 nm single crystal gold sample at an EM gain level of (a) G EM = 4 and (b) G EM = 300. Both DPs were taken with same electron beam settings except steered horizontally by a dipole coil. Each electron pulse entering the sample contained 3 × 105 electrons. There are 3.2 × 102 electrons in the (420) spot.

Image of FIG. 6.
FIG. 6.

(Color online) The bunch length evolutions along the beamline for different bunch charges (noted as before/after the collimation hole) and rf gun field gradients. For the 0.5pC/50fC and 75 MV/m case the bunch length was measured directly using the rf deflector to be 65 ± 7 fs at 1.8 from the cathode which agreed well with the simulation result.

Image of FIG. 7.
FIG. 7.

(Color online) The bunch length evolution in the velocity bunching scheme of the upgraded beamline. The DSRL is placed at 1.1 m and the collimation hole at 1.88 m. The minimum bunch length is 4 fs rms at the sample position of 1.9 m.

Image of FIG. 8.
FIG. 8.

(Color online) At (a)–(f) positions marked in Fig. 7, (row 1) the t-r charge density distributions color-coded by energy (blue to red for lower to higher energies), and (row 2) the longitudinal phase spaces tE color-coded by the radial positions (blue to red for smaller to larger radial positions).

Image of FIG. 9.
FIG. 9.

(Color online) A longitudinally rectangular (R, red), a Gaussian (G, green) and a complicated shaped (C, blue, see text for details) pulses are used to measure (a and b) an exponential decay and (c and d) an oscillating structural change. In (a) and (c) the three pulse have the same rms widths of 20 fs, and in (b) and (d) the pulses have equal fwhm widths of 4 fs.


Generic image for table
Table I.

At G EM = 300 and for the no binning and 2 × 2 binning cases the rms fluctuation of the readout level N 0, the height of the PSF S 0, and the SNR of a single MeV electron SNR0. All units are in counts.

Generic image for table
Table II.

The beam parameters at the sample in the velocity bunching scheme.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Imaging single electrons to enable the generation of ultrashort beams for single-shot femtosecond relativistic electron diffraction