Speaker
Description
Laser wakefield acceleration (LWFA) at low plasma density, $n_e \lesssim 10^{17}\,\mathrm{cm^{-3}}$, is highly desirable for generating high-energy electron beams because key accelerator figures of merit, including dephasing length and attainable energy gain, improve favorably as density is reduced. Near-infrared petawatt lasers provide a powerful route to high-energy LWFA stages in this regime, but efficient acceleration over practical distances requires driving a large-amplitude wakefield whose strength is governed by the degree of electron evacuation as well as the size of the plasma structure, the latter primarily determined by the laser spot size. Although $a_0 > 2$ is commonly used as a benchmark for accessing the highly nonlinear blowout regime, this criterion alone does not capture the critical roles of spot size and pulse duration nor the interplay among these quantities in LWFA physics; consequently, the short pulse durations and typical focusing conditions of near-infrared petawatt systems are not necessarily optimized for driving the high-amplitude, low-density blowout structures. This broader parameter dependence motivates a comparison with long-wavelength infrared drivers, such as CO$_2$ lasers, which naturally operate with pulse durations and focal geometries well matched to large low-density wakes. In this talk, we illustrate the critical roles of pulse duration and laser spot size in petawatt-class LWFA experiments aiming to access the highly nonlinear blowout regime. We further demonstrate the advantage of LWIR laser drivers in this parameter space, showing that a 15 TW, ~500 fs CO$_2$ laser pulse at $n_e = 2 \times 10^{16}\,\mathrm{cm^{-3}}$ can drive wakefields three times stronger than those obtained for BELLA- and ZEUS-scale petawatt lasers under similar conditions. This work was supported by the National Science Foundation under Grant No. PHY-2238840, U.S. Department of Energy, Office of Science under Award No. DE-SC-0014043 and resources of NERSC facility, operated under contract No. DE-AC02-5CH11231.
| Working group | WG1 |
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