Velocity map imaging of femtosecond laser induced photoelectron emission from metal nanotips

Abstract

A novel application of velocity-map imaging (VMI) is demonstrated, whereby the momentum distribution of photoelectrons ejected from a tungsten nanoscale metal tip (<50 nm radius) is recorded following illumination with an ultrafast laser pulse. The electrostatic conditions in the VMI instrument are optimized through finite element modelling, taking into account a physically realistic geometry including all conductive elements in the vicinity of the electron trajectories. The instrument is calibrated by observing above threshold ionization in krypton gas, and simultaneous electron emission from this gas and a tungsten nanotip is presented, illustrating that the velocity mapping condition is maintained. Realizing photoelectron VMI for femtosecond laser illuminated nanoscale objects will have a significant impact on the emerging field of ultrafast nanoplasmonics and will influence the development of such devices as a source of coherent pulses of electrons with applications in time-resolved microscopy, holography and diffractive imaging.

Femtosecond few- to single-electron point-projection microscopy for nanoscale dynamic imaging

“…The dynamic propagation of the fs-e pulse is modelled in GPT by assuming an emission energy of 4.5 eV and a bandwidth of 0.3 eV, in agreement with recent studies 28,31,40 . The origin of the electrons was defined as the surface of the apex of NSMT1, and the emission time defined as a Gaussian distribution with a standard deviation (SD) of 30 fs.…”

“…Femtosecond electron emission from a planar photocathode, ultracold atoms or a NSMT generally results in a kinetic energy below 5 eV and a bandwidth defined by the laser pulse spectrum 26,31,37,40 . Acceleration is necessary to minimize the kinematic dispersion due to variations in particle velocity.…”

Soft X-ray spectroscopy of nanoparticles by velocity map imaging

“…a metal tip) inside of a VMI spectrometer after interaction of the target with femtosecond laser radiation. 59,60 With proper modification of a VMI spectrometer, it should be possible to collect electrons emitted from a conductive surface. Additionally, a liquid meniscus from a small orifice (2-5 microns) in a SiN thin film has been formed and probed in an UHV environment.…”

Femtosecond transmission electron microscopy for nanoscale photonics: a numerical study

“…† The average energy of electron release from the NSMT is 0.5 eV, with a bandwidth of 0.5 eV, in agreement with previous results. 10,16,52 Following the work of Hoffrogge et al, 53 Paarmann et al 20 and Bormann et al, 21 we incorporate an electrostatic suppressor, a 50 µm thick annulus with an inner diameter of 150 µm. The NSMT protrudes 100 µm from the suppressor surface, sufficient for laser excitation.…”