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Nijhof DFJ, de Raadt TCH, Huijts JV, Franssen JGH, Mutsaers PHA, Luiten OJ. RF acceleration of ultracold electron bunches. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2023; 10:054303. [PMID: 37799710 PMCID: PMC10550337 DOI: 10.1063/4.0000200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Accepted: 08/30/2023] [Indexed: 10/07/2023]
Abstract
The ultrafast and ultracold electron source, based on laser cooling and trapping of atomic gas and its subsequent near-threshold two-step photoionization, is capable of generating electron bunches with a high transverse brightness at energies of roughly 10 keV. This paper investigates the possibility of increasing the range of applications of this source by accelerating the bunch using radio frequency electromagnetic fields. Bunch energies up to 35 keV are measured by analyzing the diffraction patterns generated from a mono-crystalline gold sample. It is found that the normalized transverse emittance is largely preserved during acceleration.
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Affiliation(s)
- D. F. J. Nijhof
- Department of Applied Physics and Science Education, Coherence and Quantum Technology Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - T. C. H. de Raadt
- Department of Applied Physics and Science Education, Coherence and Quantum Technology Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | | | | | - P. H. A. Mutsaers
- Department of Applied Physics and Science Education, Coherence and Quantum Technology Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - O. J. Luiten
- Author to whom correspondence should be addressed:
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de Raadt TCH, Franssen JGH, Luiten OJ. Subpicosecond Ultracold Electron Source. PHYSICAL REVIEW LETTERS 2023; 130:205001. [PMID: 37267545 DOI: 10.1103/physrevlett.130.205001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Revised: 03/01/2023] [Accepted: 03/29/2023] [Indexed: 06/04/2023]
Abstract
We present the first observation of subpicosecond electron bunches from an ultracold electron source. This source is based on near-threshold, two-step, femtosecond photoionization of laser-cooled rubidium gas in a grating magneto-optical trap. Bunch lengths as short as 735±7 fs (rms) have been measured in the self-compression point of the source by means of ponderomotive scattering of the electrons by a 25 fs, 800 nm laser pulse. The observed temporal structure of the electron bunch depends on the central wavelength of the ionization laser pulse, in agreement with detailed simulations of the atomic photoionization process. This shows that the bunch length limit imposed by the atomic photoionization process has been reached.
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Affiliation(s)
- T C H de Raadt
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands
| | - J G H Franssen
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands
| | - O J Luiten
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands
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Lee H, Liu X, Cultrera L, Dunham B, Kostroun VO, Bazarov IV. A cryogenically cooled high voltage DC photoemission electron source. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:083303. [PMID: 30184700 DOI: 10.1063/1.5024954] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Accepted: 07/13/2018] [Indexed: 06/08/2023]
Abstract
Linear electron accelerators and their applications such as ultrafast electron diffraction require compact high-brightness electron sources with high voltage and electric field at the photocathode to maximize the electron density and minimize space-charge induced emittance growth. Achieving high brightness from a compact source is a challenging task because it involves an often-conflicting interplay between various requirements imposed by photoemission, acceleration, and beam dynamics. Here we present a new design for a compact high voltage DC electron gun with a novel cryogenic photocathode system and report on its construction and commissioning process. This photoemission gun can operate at ∼200 kV at both room temperature and cryogenic temperature with a corresponding electric field of 10 MV/m, necessary for achieving high quality electron beams without requiring the complexity of guns, e.g., based on RF superconductivity. It hosts a compact photocathode plug compatible with that used in several other laboratories opening the possibility of generating and characterizing electron beam from photocathodes developed at other institutions.
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Affiliation(s)
- Hyeri Lee
- CLASSE, Cornell University, Ithaca, New York 14853, USA
| | - Xianghong Liu
- CLASSE, Cornell University, Ithaca, New York 14853, USA
| | - Luca Cultrera
- CLASSE, Cornell University, Ithaca, New York 14853, USA
| | - Bruce Dunham
- CLASSE, Cornell University, Ithaca, New York 14853, USA
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Franssen JGH, Frankort TLI, Vredenbregt EJD, Luiten OJ. Pulse length of ultracold electron bunches extracted from a laser cooled gas. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2017; 4:044010. [PMID: 28396879 PMCID: PMC5365419 DOI: 10.1063/1.4978996] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 03/09/2017] [Indexed: 05/19/2023]
Abstract
We present measurements of the pulse length of ultracold electron bunches generated by near-threshold two-photon photoionization of a laser-cooled gas. The pulse length has been measured using a resonant 3 GHz deflecting cavity in TM110 mode. We have measured the pulse length in three ionization regimes. The first is direct two-photon photoionization using only a 480 nm femtosecond laser pulse, which results in short (∼15 ps) but hot (∼104 K) electron bunches. The second regime is just-above-threshold femtosecond photoionization employing the combination of a continuous-wave 780 nm excitation laser and a tunable 480 nm femtosecond ionization laser which results in both ultracold (∼10 K) and ultrafast (∼25 ps) electron bunches. These pulses typically contain ∼103 electrons and have a root-mean-square normalized transverse beam emittance of 1.5 ± 0.1 nm rad. The measured pulse lengths are limited by the energy spread associated with the longitudinal size of the ionization volume, as expected. The third regime is just-below-threshold ionization which produces Rydberg states which slowly ionize on microsecond time scales.
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Affiliation(s)
| | - T L I Frankort
- Department of Applied Physics, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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Lyon M, Rolston SL. Ultracold neutral plasmas. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2017; 80:017001. [PMID: 27852983 DOI: 10.1088/0034-4885/80/1/017001] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
By photoionizing samples of laser-cooled atoms with laser light tuned just above the ionization limit, plasmas can be created with electron and ion temperatures below 10 K. These ultracold neutral plasmas have extended the temperature bounds of plasma physics by two orders of magnitude. Table-top experiments, using many of the tools from atomic physics, allow for the study of plasma phenomena in this new regime with independent control over the density and temperature of the plasma through the excitation process. Characteristic of these systems is an inhomogeneous density profile, inherited from the density distribution of the laser-cooled neutral atom sample. Most work has dealt with unconfined plasmas in vacuum, which expand outward at velocities of order 100 m/s, governed by electron pressure, and with lifetimes of order 100 μs, limited by stray electric fields. Using detection of charged particles and optical detection techniques, a wide variety of properties and phenomena have been observed, including expansion dynamics, collective excitations in both the electrons and ions, and collisional properties. Through three-body recombination collisions, the plasmas rapidly form Rydberg atoms, and clouds of cold Rydberg atoms have been observed to spontaneously avalanche ionize to form plasmas. Of particular interest is the possibility of the formation of strongly coupled plasmas, where Coulomb forces dominate thermal motion and correlations become important. The strongest impediment to strong coupling is disorder-induced heating, a process in which Coulomb energy from an initially disordered sample is converted into thermal energy. This restricts electrons to a weakly coupled regime and leaves the ions barely within the strongly coupled regime. This review will give an overview of the field of ultracold neutral plasmas, from its inception in 1999 to current work, including efforts to increase strong coupling and effects on plasma properties due to strong coupling.
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Affiliation(s)
- M Lyon
- Joint Quantum Institute, University of Maryland, College Park and NIST, College Park, MD 20742, USA
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Bainbridge AR, Barlow Myers CW, Bryan WA. Femtosecond few- to single-electron point-projection microscopy for nanoscale dynamic imaging. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2016; 3:023612. [PMID: 27158637 PMCID: PMC4841798 DOI: 10.1063/1.4947098] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 04/07/2016] [Indexed: 05/08/2023]
Abstract
Femtosecond electron microscopy produces real-space images of matter in a series of ultrafast snapshots. Pulses of electrons self-disperse under space-charge broadening, so without compression, the ideal operation mode is a single electron per pulse. Here, we demonstrate femtosecond single-electron point projection microscopy (fs-ePPM) in a laser-pump fs-e-probe configuration. The electrons have an energy of only 150 eV and take tens of picoseconds to propagate to the object under study. Nonetheless, we achieve a temporal resolution with a standard deviation of 114 fs (equivalent to a full-width at half-maximum of 269 ± 40 fs) combined with a spatial resolution of 100 nm, applied to a localized region of charge at the apex of a nanoscale metal tip induced by 30 fs 800 nm laser pulses at 50 kHz. These observations demonstrate real-space imaging of reversible processes, such as tracking charge distributions, is feasible whilst maintaining femtosecond resolution. Our findings could find application as a characterization method, which, depending on geometry, could resolve tens of femtoseconds and tens of nanometres. Dynamically imaging electric and magnetic fields and charge distributions on sub-micron length scales opens new avenues of ultrafast dynamics. Furthermore, through the use of active compression, such pulses are an ideal seed for few-femtosecond to attosecond imaging applications which will access sub-optical cycle processes in nanoplasmonics.
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Affiliation(s)
| | - C W Barlow Myers
- Department of Physics, College of Science, Swansea University , Singleton Park, Swansea SA2 8PP, United Kingdom
| | - W A Bryan
- Department of Physics, College of Science, Swansea University , Singleton Park, Swansea SA2 8PP, United Kingdom
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Murphy D, Scholten RE, Sparkes BM. Increasing the Brightness of Cold Ion Beams by Suppressing Disorder-Induced Heating with Rydberg Blockade. PHYSICAL REVIEW LETTERS 2015; 115:214802. [PMID: 26636853 DOI: 10.1103/physrevlett.115.214802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Indexed: 06/05/2023]
Abstract
A model for the equilibrium coupling of an ion system with varying initial hard-sphere Rydberg blockade correlations is used to quantify the suppression of disorder-induced heating in Coulomb-expanding cold ion bunches. We show that bunches with experimentally achievable blockade parameters have an emittance reduced by a factor of 2.6 and increased focusability and brightness compared to a disordered bunch. Demonstrating suppression of disorder-induced heating is an important step in the development of techniques for the creation of beam sources with sufficient phase-space density for ultrafast, single-shot coherent diffractive imaging.
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Affiliation(s)
- D Murphy
- School of Physics, The University of Melbourne, Victoria 3010, Australia
| | - R E Scholten
- School of Physics, The University of Melbourne, Victoria 3010, Australia
| | - B M Sparkes
- School of Physics, The University of Melbourne, Victoria 3010, Australia
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Lee H, Karkare S, Cultrera L, Kim A, Bazarov IV. Review and demonstration of ultra-low-emittance photocathode measurements. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:073309. [PMID: 26233374 DOI: 10.1063/1.4927381] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
This paper reports the development of a simple and reliable apparatus for measuring ultra-low emittance, or equivalently the mean transverse energy from cryogenically cooled photocathodes. The existing methods to measure ultra-low emittance from photocathodes are reviewed. Inspired by the available techniques, we have implemented two complementary methods, the waist scan and voltage scan, in one system giving consistent results. Additionally, this system is capable of measuring the emittance at electric fields comparable to those obtained in DC photoinjectors.
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Affiliation(s)
- Hyeri Lee
- CLASSE, Cornell University, Ithaca, New York 14850, USA
| | | | - Luca Cultrera
- CLASSE, Cornell University, Ithaca, New York 14850, USA
| | - Andrew Kim
- CLASSE, Cornell University, Ithaca, New York 14850, USA
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9
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Analytical model of an isolated single-atom electron source. Ultramicroscopy 2014; 147:61-9. [PMID: 25062039 DOI: 10.1016/j.ultramic.2014.07.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2013] [Revised: 06/26/2014] [Accepted: 07/06/2014] [Indexed: 11/20/2022]
Abstract
An analytical model of a single-atom electron source is presented, where electrons are created by near-threshold photoionization of an isolated atom. The model considers the classical dynamics of the electron just after the photon absorption, i.e. its motion in the potential of a singly charged ion and a uniform electric field used for acceleration. From closed expressions for the asymptotic transverse electron velocities and trajectories, the effective source temperature and the virtual source size can be calculated. The influence of the acceleration field strength and the ionization laser energy on these properties has been studied. With this model, a single-atom electron source with the optimum electron beam properties can be designed. Furthermore, we show that the model is also applicable to ionization of rubidium atoms, and thus also describes the ultracold electron source, which is based on photoionization of laser-cooled alkali atoms.
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van Mourik MW, Engelen WJ, Vredenbregt EJD, Luiten OJ. Ultrafast electron diffraction using an ultracold source. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2014; 1:034302. [PMID: 26798777 PMCID: PMC4711599 DOI: 10.1063/1.4882074] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Accepted: 05/27/2014] [Indexed: 05/12/2023]
Abstract
The study of structural dynamics of complex macromolecular crystals using electrons requires bunches of sufficient coherence and charge. We present diffraction patterns from graphite, obtained with bunches from an ultracold electron source, based on femtosecond near-threshold photoionization of a laser-cooled atomic gas. By varying the photoionization wavelength, we change the effective source temperature from 300 K to 10 K, resulting in a concomitant change in the width of the diffraction peaks, which is consistent with independently measured source parameters. This constitutes a direct measurement of the beam coherence of this ultracold source and confirms its suitability for protein crystal diffraction.
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Affiliation(s)
- M W van Mourik
- Department of Applied Physics, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - W J Engelen
- Department of Applied Physics, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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