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Title: Field Emission Tip as a Nanometer Source of Free Electron Femtosecond Pulses

Abstract

We report a source of free electron pulses based on a field emission tip irradiated by a low-power femtosecond laser. The electron pulses are shorter than 70 fs and originate from a tip with an emission area diameter down to 2 nm. Depending on the operating regime we observe either photofield emission or optical field emission with up to 200 electrons per pulse at a repetition rate of 1 GHz. This pulsed electron emitter, triggered by a femtosecond oscillator, could serve as an efficient source for time-resolved electron interferometry, for time-resolved nanometric imaging and for synchrotrons.

Authors:
; ; ;  [1]
  1. Physics Department, Stanford University, Stanford, California 94305 (United States)
Publication Date:
OSTI Identifier:
20778657
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 96; Journal Issue: 7; Other Information: DOI: 10.1103/PhysRevLett.96.077401; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ELECTRON SOURCES; ELECTRONS; FIELD EMISSION; GHZ RANGE 01-100; INTERFEROMETRY; IRRADIATION; LASERS; OSCILLATORS; PULSES; SYNCHROTRONS; TIME RESOLUTION

Citation Formats

Hommelhoff, Peter, Sortais, Yvan, Aghajani-Talesh, Anoush, and Kasevich, Mark A. Field Emission Tip as a Nanometer Source of Free Electron Femtosecond Pulses. United States: N. p., 2006. Web. doi:10.1103/PHYSREVLETT.96.0.
Hommelhoff, Peter, Sortais, Yvan, Aghajani-Talesh, Anoush, & Kasevich, Mark A. Field Emission Tip as a Nanometer Source of Free Electron Femtosecond Pulses. United States. doi:10.1103/PHYSREVLETT.96.0.
Hommelhoff, Peter, Sortais, Yvan, Aghajani-Talesh, Anoush, and Kasevich, Mark A. Fri . "Field Emission Tip as a Nanometer Source of Free Electron Femtosecond Pulses". United States. doi:10.1103/PHYSREVLETT.96.0.
@article{osti_20778657,
title = {Field Emission Tip as a Nanometer Source of Free Electron Femtosecond Pulses},
author = {Hommelhoff, Peter and Sortais, Yvan and Aghajani-Talesh, Anoush and Kasevich, Mark A.},
abstractNote = {We report a source of free electron pulses based on a field emission tip irradiated by a low-power femtosecond laser. The electron pulses are shorter than 70 fs and originate from a tip with an emission area diameter down to 2 nm. Depending on the operating regime we observe either photofield emission or optical field emission with up to 200 electrons per pulse at a repetition rate of 1 GHz. This pulsed electron emitter, triggered by a femtosecond oscillator, could serve as an efficient source for time-resolved electron interferometry, for time-resolved nanometric imaging and for synchrotrons.},
doi = {10.1103/PHYSREVLETT.96.0},
journal = {Physical Review Letters},
number = 7,
volume = 96,
place = {United States},
year = {Fri Feb 24 00:00:00 EST 2006},
month = {Fri Feb 24 00:00:00 EST 2006}
}
  • We present a nano-scale photoelectron source, optimized for ultrashort pulse durations and well-suited for time-resolved diffraction and advanced laser acceleration experiments. A tungsten tip of several-ten-nanometers diameter mounted in a suppressor-extractor electrode configuration allows the generation of 30 keV electron pulses with an estimated pulse duration of 9 fs (standard deviation; 21 fs full width at half maximum) at the gun exit. We infer the pulse duration from particle tracking simulations, which are in excellent agreement with experimental measurements of the electron-optical properties of the source in the spatial domain. We also demonstrate femtosecond-laser triggered operation of the apparatus. The temporal broadening ofmore » the pulse upon propagation to a diffraction sample can be greatly reduced by collimating the beam. Besides the short electron pulse duration, a tip-based source is expected to feature a large transverse coherence and a nanometric emittance.« less
  • Abstract is not available
  • Femtosecond pulses from soft-x-ray free-electron lasers (FELs) [1] are ideal for directly probing matter at atomic length scales and timescales of atomic motion. An important component of understanding ultrafast phenomena of light-matter interactions is concerned with the onset of atomic motion which is impeded by the atoms inertia. This delay of structural changes will enable atomic-resolution flash-imaging [2-3] to be performed at upcoming x-ray FELs [4-5] with pulses intense enough to record the x-ray scattering from single molecules [6]. We explored this ultrafast high-intensity regime with the FLASH soft-x-ray FEL [7-8] by measuring the reflectance of nanostructured multilayer mirrors usingmore » pulses with fluences far in excess of the mirrors damage threshold. Even though the nanostructures were ultimately completely destroyed, we found that they maintained their integrity and reflectance characteristics during the 25-fs-long pulse, with no evidence for any structural changes during that time over lengths greater than 3 {angstrom}. In the recently built FLASH FEL [7], x-rays are produced from short electron pulses oscillating in a periodic magnet array, called an undulator, by the principle of self-amplification of spontaneous emission [9-10]. The laser quality of the x-ray pulses can be quantified by the peak spectral brilliance of the source, which is 10{sup 28} photons/(s mm2 mrad2 0.1% bandwidth) [8]; this is up to seven orders of magnitude higher than modern third-generation synchrotron sources. For our studies, the machine operated with pulses of 25 fs duration at a wavelength of 32.5 nm and energies up to 21 {micro}J. We focused these pulses to 3 x 10{sup 14} W/cm{sup 2} onto our nanostructured samples, resulting in an the unprecedented heating rate of 5 x 10{sup 18} K/s, while probing the irradiated structures at the nanometer length scale. The x-ray reflectivity of periodic nanometer-scale multilayers [11] is very sensitive to changes in the atomic positions and the refractive indices of the constituent materials, making them an ideal choice to study structural changes induced by ultrashort FEL pulses. The large multilayer reflectivity results from the cooperative interaction of the x-ray field with many layers of precisely fabricated thicknesses, each less than the x-ray wavelength. This Bragg or resonant reflection from the periodic structure is easily disrupted by any imperfection of the layers. The characteristics of the structure, such as periodicity or layer intermixing, can be precisely determined from the measurement of the Bragg reflectivity as a function of incidence angle. These parameters can be easily measured to a small fraction of the probe wavelength, as is well known in x-ray crystallography where average atomic positions of minerals or proteins are found to less than 0.01{angstrom}. Thus, we can explore ultrafast phenomena at length scales less than the wavelength, and investigate the conditions to overcome the effects of radiation damage by using ultrafast pulses.« less
  • An original and reliable technique, based on a three-wave interaction, has been designed and successfully tested to analyze the evolution of the modes and the pulse length of a free-electron laser during the buildup of the radiation. The technique was developed in order to study the effects of the optical guiding in the free-electron laser built at Stanford and driven by the MARK III linear accelerator. We explicitly mention that this technique can be easily exploited to monitor, in real time, the pulse-to-pulse fluctuations of the mode size and the pulse length of the pulses delivered by any laser independentlymore » of its pulse length from femtosecond to millisecond.« less