High repetition ultrafast electron bunches

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Gigahertz repetition rate thermionic electron gun concept

\u3cp\u3eWe present a novel concept for the generation of gigahertz repetition rate high brightness electron bunches. A custom design 100 kV thermionic gun provides a continuous electron beam, with the current determined by the filament size and temperature. A 1 GHz rectangular rf cavity deflects the beam across a knife-edge, creating a pulsed beam. Adding a higher harmonic mode to this cavity results in a flattened magnetic field profile which increases the duty cycle to 30%. Finally, a compression cavity induces a negative longitudinal velocity-time chirp in a bunch, initiating ballistic compression. Adding a higher harmonic mode to this cavity increases the linearity of this chirp and thus decreases the final bunch length. Charged particle simulations show that with a 0.15 mm radius LaB6 filament held at 1760 K, this method can create 279 fs, 3.0 pC electron bunches with a radial rms core emittance of 0.089 mm mrad at a repetition rate of 1 GHz.\u3c/p\u3

Design and experimental validation of a compact collimated Knudsen source

In this paper we discuss the design and performance of a collimated Knudsen source which has the benefit of a simple design over recirculating sources. Measurements of the flux, transverse velocity distribution and brightness at different temperatures were conducted to evaluate the performance. The scaling of the flux and brightness with the source temperature follow the theoretical predictions. The transverse velocity distribution in the transparent operation regime also agrees with the simulated data. The source was found able to produce a flux of $10^{14}$ s$^{-1}$ at a temperature of 433 K. Furthermore the transverse reduced brightness of an ion beam with equal properties as the atomic beam reads $1.7 \times 10^2$ A/(m${}^2$ sr eV) which is sufficient for our goal: the creation of an ultra-cold ion beam by ionization of a laser-cooled and compressed atomic rubidium beam

Cavity-enhanced photoionization of an ultracold rubidium beam for application in focused ion beams

A two-step photoionization strategy of an ultracold rubidium beam for application in a focused ion beam instrument is analyzed and implemented. In this strategy the atomic beam is partly selected with an aperture after which the transmitted atoms are ionized in the overlap of a tightly cylindrically focused excitation laser beam and an ionization laser beam whose power is enhanced in a build-up cavity. The advantage of this strategy, as compared to without the use of a build-up cavity, is that higher ionization degrees can be reached at higher currents. Optical Bloch equations including the photoionization process are used to calculate what ionization degree and ionization position distribution can be reached. Furthermore, the ionization strategy is tested on an ultracold beam of 85Rb atoms. The beam current is measured as a function of the excitation and ionization laser beam intensity and the selection aperture size. Although details are different, the global trends of the measurements agree well with the calculation. With a selection aperture diameter of 52μm, a current of (170±4) pA is measured, which according to calculations is 63% of the current equivalent of the transmitted atomic flux. Taking into account the ionization degree the ion beam peak reduced brightness is estimated at 1×107 A/(m2sreV)

Ultracold ion beams using laser cooling

Focused ion beam instruments a re indispensable tools for the semiconductor industry due to their ability to image and modify structures on the nanometer length scale. For milling and deposition, the industry standard is the gallium liquid-metal ion source which enables a resorution of 5-10 nm at a current of a few pA. with the quest towards smaller features on integrated circuits, there is a need for novel ion sources that allow for better resolution. Several research groups are working towards applying laser-intensified alkali-metal ion beams for this purpose [1]. s-uch ultra-low temperature (1 mK) ion beams can be created by lasercooling and photo-ionization of a thermal atomic beam or vapor. The Rb ion source under development in Eindhoven in collaboration with FEI

Novel electron bunch creation towards ultrafast electron diffraction

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Growing Magnetic Nanostructures by Atom Lithography

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Dual mode microwave deflection cavities for ultrafast electron microscopy

\u3cp\u3eThis 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 a dual mode. This elliptical cavity supports two orthogonal TM\u3csub\u3e110\u3c/sub\u3e 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 τ = (750 ± 10) fs pulse duration are created with only (2.4 ± 0.1) W of microwave input power; with normalized rms emittances of ϵ\u3csub\u3en,x\u3c/sub\u3e = (2.1 ± 0.2) pm rad and ϵ\u3csub\u3en,y\u3c/sub\u3e = (1.3 ± 0.2) pm rad for a peak current of I\u3csub\u3ep\u3c/sub\u3e = (0.4 ± 0.1) nA. This corresponds to an rms normalized peak brightness of B n p , rms = ( 7 ± 1 ) × 10 6 A/m\u3csup\u3e2\u3c/sup\u3e sr V, equal to previous measurements for the continuous beam. In addition, the FWHM energy spread of ΔU = (0.90 ± 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 electron energy loss spectroscopy detector with a dynamic range >10\u3csup\u3e4\u3c/sup\u3e.\u3c/p\u3