Strong-field above-threshold photoemission from sharp metal tips (1009.2872v1)

Abstract: We present energy-resolved measurements of electron emission from sharp metal tips driven with low energy pulses from a few-cycle laser oscillator. We observe above-threshold photoemission with a photon order of up to 9. At a laser intensity of 2*10^11 W/cm^2 suppression of the lowest order peak occurs, indicating the onset of strong-field effects. We also observe peak shifting linearly with intensity with a slope of around -1.8eV / (10^12 W/cm^2). We attribute the magnitude of the laser field effects to field enhancement taking place at the tip's surface.

Insightful Overview of "Strong-field above-threshold photoemission from sharp metal tips"

The research presented in "Strong-field above-threshold photoemission from sharp metal tips" explores the domain of above-threshold photoemission (ATP), marking significant advancements in our understanding of laser-induced electron emission from sharp metallic tips. Conducted by Schenk, Krüger, and Hommelhoff at the Max-Planck-Institut für Quantenoptik, the paper employs low-energy few-cycle laser pulses to investigate strong-field effects and their implications for nanoscale electron emitters.

The paper offers notable contributions in the following areas:

1. Experimental Methodology and Observations: Utilizing tungsten tips irradiated with femtosecond laser pulses, the research meticulously measures electron energies, capturing a photon order of up to 9. The setup demonstrates ATP's potential to elucidate the physics of multiphoton processes, an area predominantly explored via above-threshold ionization (ATI) until now. Notably, this work registers strong-field effects, characterized by peak suppression akin to ATI's threshold phenomena, a first in ATP contexts.
2. Field Enhancement and Strong-field Manifestations: A critical component of the paper is the interaction of intense laser fields with the metallic surface, leading to field enhancement effects. This enhancement allows the detection of strong-field effects at comparably low laser intensities, signified by phenomena such as the observed linear peak shifts proportional to laser intensity—a clear indication of light-induced continuum shifts.
3. Theoretical Implications: The data suggest an intricate interplay between the emitted electrons’ initial and continuum states, where the photoemission process does not necessitate the electrons’ energy to cover both the barrier potential and the quiver energy in the laser field classically. The field enhancement is quantified, indicating an amplification factor in the range of previously documented experiments on similar systems.
4. Potential Applications: Practical applications are envisioned in the arena of ultrafast laser-driven nanoemitters. These findings hold promise for developing low-emittance electron sources for next-generation free electron lasers. The implications extend towards precision ATI studies at atomic and molecular scales, where stark field effects can be exploited in the presence of a high repetition rate laser.
5. Future Directions: A forthcoming exploration involves the potential application of nanometric electron emitters within high-harmonic generation (HHG) frameworks, offering unprecedented spatial resolution. Moreover, the ability to apply concomitant static and dynamic fields could lead to novel mechanisms for controlling electronic motion.

The paper's nuanced approach opens numerous avenues for further research, especially in exploiting nano-scaled ATP studies for broader applications such as attosecond science and electron source development. As such, this work represents a pivotal step in both experimental techniques and theoretical understandings of strong-field laser-matter interactions at the nanoscale.