Nonadiabatic ponderomotive effects in photoemission from nanotips in intense midinfrared laser fields

Schötz, Johannes; Mitra, Sambit; Fuest, Harald; Neuhaus, Marcel; Okell, William; Förster, M.; Paschen, Timo; Ciappina, M. F.; Yanagisawa, Hirofumi; Wnuk, Paweł; Hommelhoff, Peter; Kling, Matthias F.

doi:10.1103/physreva.97.013413

Cited by 15 publications

(12 citation statements)

References 43 publications

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“…On the one hand, the ATI spectrum quickly collapses in the limit of very strong field localization for decay lengths approaching the electron quiver amplitude (red horizontal line). In this limit, recollision becomes suppressed and eventually quenched [19]. The spectral positions of the ATI peaks, however, remain unchanged.…”

Section: Resultsmentioning

confidence: 95%

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

Seiffert¹,

Paschen²,

Hommelhoff³

et al. 2018

J. Phys. B: At. Mol. Opt. Phys.

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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.

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Section: Resultsmentioning

confidence: 95%

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

Seiffert¹,

Paschen²,

Hommelhoff³

et al. 2018

J. Phys. B: At. Mol. Opt. Phys.

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“…Therefore, we neglect the influence of the finite longitudinal coherence of the beam that is normally of less influence on the transverse spatial coherence. 28,58 In the above calculation, this was implied by assuming that the longitudinal phase propagation is given by (27) without finite longitudinal energy spread.…”

Section: Calculation Of the Transverse Structure Of Field Emissimentioning

confidence: 99%

“…The transverse structure of the wave function also has a large impact on the recently studied ultrafast electron dynamics at the field emitter apex, where the large amplitude oscillating electric field of a few cycle laser pulses induces the field emission and forced oscillation and re-scattering at the tip apex, resulting in a rich variety of nanoscale strong field physics. [24][25][26][27] These effects might be significantly diminished unless the transverse spread of the wave function during the propagation near the tip apex was a) restricted. Despite the prior success of the wave optical analysis of such experiments by using the theory of the partially coherent optical beams, [28][29][30] experiments are often in a diode configuration, in which electrons emitted from the cathodes are accelerated toward the samples or anodes, hence, such optical theory neglecting the acceleration is of limited validity.…”

Section: Introductionmentioning

confidence: 99%

Transverse structure of the wave function of field emission electron beam determined by intrinsic transverse energy

Tsujino

2018

Journal of Applied Physics

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The average transverse energy of field emission electrons at the cathode surface is one of the key factors that determines the virtual source size, hence the transverse spatial coherence of field emitters. In the past, the subject has been intensively studied by classical electron optics analysis but its wave optical studies are rare. In this work, we therefore aim to elucidate the influence of the transverse momentum in solid on the transverse structure of the wave function of field emission electrons. From the calculation extending the standard field emission theory within the WKB approximation for model planar free-electron metal, we obtained a Gaussian-beam-type wave function that exhibits a minimum transverse width at the cathode surface as determined by the average transverse energy and propagates the first few nanometers with a limited transverse spread. At far field, the wave function spreads as the electron propagates away from the cathode surface. Comparison with classical results indicated that, in the present planar field emitter model, the neglect of the three-dimensional potential around the tip apexes of actual field emitters underestimates the transverse spread up to a factor of 2. However, when the cathode size is finite and the electrons in the solid are phase-coherent within the source area, the transverse spread is much smaller than that of the point-source wave function. Our result indicates that the intrinsic transverse emittance of a finite size fully coherent field emitter is much smaller than the value predicted by classical analysis. Published by AIP Publishing. https://doi.

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“…By performing LFEM together with spectroscopic experiments, previous works revealed intriguing atto-to femtosecond electron dynamics within nanometer areas, such as plasmonic effects [6][7][8][9][10][11][12][13]27], ultrafast coherent electron emission [10,11], femtosecond photoexcitation dynamics [9,[14][15][16], heating effects [16,17], optical tunneling emission [18][19][20][21][22][23][24][25][26][27][28][29], * hirofumi.yanagisawa@mpq.mpg.de ultrafast rectification effects [22], attosecond near-field sampling [25,26], elastic and inelastic rescattering processes [19,23,24,26], and subcycle emission [20,22,28]. In particular, plasmonic effects play a central role in the laser-induced electron emission from a nanotip because they create nanoscale optical fields on the tip apex [6].…”

Section: Introductionmentioning

confidence: 99%

“…The photoexcited electrons are then emitted into a vacuum either through the potential barrier or over the barrier [6][7][8][9][10][11][12][13][14][15][16]. In the strong-field regime, in addition to the photoexcitation, the laser field modifies the surface potential barrier and causes tunneling emission [18][19][20][21][22][23][24][25][26][27][28][29]. Once in the vacuum, the emitted electrons experience acceleration and deceleration due to the oscillating laser field.…”

Section: Introductionmentioning

confidence: 99%

Laser-induced field emission from a tungsten nanotip by circularly polarized femtosecond laser pulses

et al. 2020

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We have investigated emission patterns and energy spectra of electrons from a tungsten nanotip induced by circularly polarized femtosecond laser pulses. Variations of emission patterns were observed for different helicities of circular polarization while the energy spectra remained almost identical. The physics behind this difference in emission patterns is the change in propagation directions of surface electromagnetic waves on the tip apex. The energy spectra showed the same spectroscopic signatures as the linearly polarized laser in a strong-field regime, which are a low-energy peak and a plateau feature. The low-energy peak is due to a delayed electron emission with respect to a prompt emission. The experimental data and plasmonic simulations support our previous conclusion, where the observed delayed emission processes originate from an inelastic rescattering process. This work demonstrates that the use of circular polarization is an easy means to add extra knobs to control the spatial and temporal emission from a nanotip at the nanometer and femtosecond scale. It could find applications as a helicity-driven subcycle optical switch.We have investigated emission patterns and energy spectra of electrons from a tungsten nanotip induced by circularly polarized femtosecond laser pulses. Variations of emission patterns were observed for different helicities of circular polarization while the energy spectra remained almost identical. The physics behind this difference in emission patterns is the change in propagation directions of surface electromagnetic waves on the tip apex. The energy spectra showed the same spectroscopic signatures as the linearly polarized laser in a strong-field regime, which are a low-energy peak and a plateau feature. The low-energy peak is due to a delayed electron emission with respect to a prompt emission. The experimental data and plasmonic simulations support our previous conclusion, where the observed delayed emission processes originate from an inelastic rescattering process. This work demonstrates that the use of circular polarization is an easy means to add extra knobs to control the spatial and temporal emission from a nanotip at the nanometer and femtosecond scale. It could find applications as a helicity-driven subcycle optical switch.

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Nonadiabatic ponderomotive effects in photoemission from nanotips in intense midinfrared laser fields

Cited by 15 publications

References 43 publications

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

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

Transverse structure of the wave function of field emission electron beam determined by intrinsic transverse energy

Laser-induced field emission from a tungsten nanotip by circularly polarized femtosecond laser pulses

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