High-order above-threshold photoemission from nanotips controlled with two-color laser fields

Abstract

We investigate the process of phase-controlled high-order abovethreshold photoemission from sharp metallic nanotips under bichromatic laser fields. Experimental photoelectron spectra resulting from two-color excitation with a moderately intense near-infrared fundamental field (1560 nm) and its weak second harmonic show a strong sensitivity on the relative phase and clear indications for a plateau-like structure that is attributed to elastic backscattering. To explore the relevant control mechanisms, characteristic features, and particular signatures from near-field inhomogeneity, we performed systematic quantum simulations employing a one-dimensional nanotip model.Besides rich phase-dependent structures in the simulated above-threshold ionization (ATI) photoelectron spectra we find ponderomotive shifts as well as substantial modifications of the rescattering cutoff as function of the decay length of the near-field. To explore the quantum or classical nature of the observed features and to discriminate the two-color effects stemming from electron propagation and from the ionization rate we compare the quantum results to classical trajectory simulations. We show that signatures from direct electrons as well as the modulations in the plateau region mainly stem from control of the ionization probability, while the modulation in the cutoff region can only be explained by the impact of the two-color field on the electron trajectory. Despite the complexity of the phase-dependent features that render two-color strong-field photoemission from nanotips intriguing for sub-cycle strong-field control, our findings support that the recollision features in the cutoff region provide a robust and reliable method to calibrate the relative two-color phase.

All-optical spatio-temporal control of electron emission from SiO2 nanospheres with femtosecond two-color laser fields

“…These results demonstrate the feasibility of using two-color laser fields for the control of the emission direction of the most energetic electrons from nanoparticles. This observation goes beyond the recently shown two-color control of the cutoff in the electron emission from metallic nanotips [3,4,39].…”

“…In principle, the presence of the 2ω field component can affect both the magnitude and spatial distribution of the ionization rate as well as the trajectory dynamics of the released electrons. The relative contributions of the effects of the 2ω field on the ionization rate and the trajectory propagation can be revealed by performing a selective activation in the SMM simulations, in analogy to the analysis in [4]. In figure 6 we show (a) the predicted angular and phase-resolved electron cutoff energies with the 2ω field included in the trajectory propagation but neglected in the ionization rate (here just driven by the ω field) and (b) for the 2ω field included in the ionization process, but propagation just driven by the ω field.…”

“…Intense laser pulses with tailored waveforms have proven to be a powerful tool for the control of electron dynamics in atomic, molecular, and solid targets [1][2][3][4][5][6][7][8][9][10][11][12]. The laser electric field of such pulses exerts a force that varies on the attosecond time scale for visible light and enables the steering of electron motion on sub-cycle time scales and on nanometer spatial dimensions or even below [13][14][15][16][17].…”

Ultrafast Field‐Emission Electron Sources Based on Nanomaterials

“…The photocurrent follows a power law of the form P n , where P refers to the laser power and the exponent n refers to the number of photons absorbed. In this multiphoton scheme, more than the minimum required number of photons can be absorbed, referred to as above‐threshold multiphoton photoemission (Figure D). The time scale of the multiphoton photoemission is the same as the width of the laser pulse.…”

Ultrashort field emission in metallic nanostructures and low-dimensional carbon materials

“…The high contrast was attributed to the quantum-pathway interference between the 4-photon absorption and the 2-photon absorption accompanied by 1-photon absorption of 780 nm. Furthermore, two-color laser field irradiation was found to introduce a quenching of the electron backscattering and the variation of maximum kinetic energy, as shown in Figure 4(b) [92].…”