High-order harmonic generation from solid targets with 2 mJ pulses.

Area of Science:

• Physics
• Laser Science
• Nonlinear Optics

Background:

• High-harmonic generation (HHG) is a key process for producing coherent extreme ultraviolet (XUV) and soft X-ray radiation.
• Traditional HHG predominantly utilizes gas-phase media, limiting achievable photon energies and flux.
• Solid targets offer a pathway to higher harmonic orders and potentially more compact HHG sources.

Purpose of the Study:

• To demonstrate high-harmonic generation (HHG) from solid targets using a kilohertz laser system.
• To investigate the feasibility of using a very short focal length optic (f/1.4 paraboloid) for solid-state HHG.
• To characterize the generated harmonics in terms of order, divergence, and conversion efficiency.

Main Methods:

• Focusing 2 mJ, 50 fs laser pulses at 800 nm to a 1.7 μm spot size (FWHM) on solid targets.
• Utilizing a very short focal length paraboloid (f/1.4) in conjunction with a kilohertz repetition rate laser system.
• Operating the system at 500 Hz without employing contrast enhancement techniques.

Main Results:

• Generation of harmonics up to the 18th order from solid targets.
• Achieved low harmonic divergence (<4°) compared to the driving laser beam.
• Observed conversion efficiencies per harmonic greater than 10⁻⁷, comparable to gas-phase HHG.
• Demonstrated HHG using a short focal length optic and a kilohertz laser system, a novel approach.

Conclusions:

• High-harmonic generation from solid targets is feasible with short focal length optics and kilohertz laser systems.
• The generated harmonics exhibit favorable properties, including low divergence and competitive conversion efficiencies.
• This work paves the way for more compact and efficient sources of coherent XUV and soft X-ray radiation.