Strong-field ionization of clusters using two-cycle pulses at 1.8 μm

Area of Science:

• Plasma physics
• Atomic and molecular physics
• Laser-driven particle acceleration

Background:

• Previous studies focused on longer laser pulses (many optical cycles) interacting with nanoscale particles.
• Investigations typically used near-infrared to X-ray laser pulses.

Purpose of the Study:

• To explore strong-field ionization of rare-gas clusters using ultrashort, two-cycle 1.8 μm laser pulses.
• To access a new interaction regime where electron dynamics are laser-dominated and atomic motion is negligible.

Main Methods:

• Irradiation of rare-gas clusters (10^3–10^5 atoms) with two-cycle 1.8 μm laser pulses at an intensity of 1 × 10^15 W/cm^2.
• Comparison with experiments using 800 nm laser pulses of similar intensity and duration.
• Analysis of emitted electron energies and emission directionality.

Main Results:

• Observation of fast electron emission exceeding 3 keV at 1.8 μm, significantly higher than electrons below 500 eV at 800 nm.
• Preferential emission of energetic electrons along the laser polarization direction.
• Evidence of an electron rescattering plateau in addition to direct emission.

Conclusions:

• Ultralong wavelength laser pulses enable a new regime for generating energetic electrons from rare-gas clusters.
• Scaling to longer wavelengths is predicted to produce highly directional, energetic electron currents on femtosecond timescales.