Description
A multi-terawatt, picosecond Long-Wave Infrared (LWIR) laser operating at λ = 9.2 μm supports a broad user program in strong-field and plasma physics at the Accelerator Test Facility (ATF) of Brookhaven National Laboratory. The unique advantages of LWIR—such as the λ-proportional increase in photon number per joule, λ² scaling of the ponderomotive force and electron energy, and λ⁻² dependence of the critical plasma density—enable experimental regimes not readily accessible with shorter-wavelength lasers.
This presentation highlights recent ATF experiments using the LWIR laser in conjunction with a 75-MeV electron LINAC. These include pioneering studies of plasma-based acceleration of electrons and ions, nonlinear Compton scattering, and related phenomena. We also describe the current status of LWIR laser technology and planned upgrades targeting few-cycle, femtosecond-scale operation, with normalized vector potentials reaching a₀ = 10–30, and the potential for future extension toward a₀ ≈ 100.
Next-generation, ultra-intense LWIR lasers will complement state-of-the-art petawatt (PW) and multi-PW near-IR systems envisioned for probing linear and nonlinear QED processes in extreme fields. For instance, a 9-μm laser pulse with a peak intensity of ~10²⁰ W/cm² and a duration of just three optical cycles can produce ponderomotive effects equivalent to those from a 10²² W/cm² Ti:sapphire laser. The longer wavelength, with proportionally larger focal spot sizes and pulse durations, may also help enhance interaction throughput.
Coupling the LWIR laser with relativistic electron beams and near-IR lasers further expands the experimental capabilities of facilities like ATF. Potential research directions include broadband photon generation via nonlinear Compton scattering, heavy-ion acceleration, the development of collider- and FEL-quality electron beams from plasma, avalanche multiplication of electron-positron pairs in vacuum seeded by electron-beam interactions with solid targets, and studies of frequency up-conversion and intensity amplification via relativistic oscillating mirrors.
