Generation of 10-m-lengthscale plasma columns by resonant and off-resonant laser pulses

TL;DR

This study compares resonant and off-resonant ultra-short laser pulses in creating 10-meter-long plasma columns in rubidium vapor, demonstrating that resonant pulses produce more confined and homogeneous plasma channels suitable for advanced applications.

Contribution

It provides experimental and simulation evidence that resonant laser pulses are more effective than off-resonant pulses in generating long, uniform plasma columns in rubidium vapor.

Findings

Resonant pulses create more confined plasma channels.

Off-resonant pulses result in wider, less uniform plasma.

Resonant pulses are more energy-efficient for long plasma generation.

Abstract

Creating extended, highly homogeneous plasma columns like that required by plasma wakefield accelerators can be a challenge. We study the propagation of ultra-short, TW power ionizing laser pulses in a 10-meter-long rubidium vapor and the plasma columns they create. We perform experiments and numerical simulations for pulses with 780 nm central wavelength, which is resonant with the D$_2$ transition from the ground state of rubidium atoms, as well as for pulses with 810 nm central wavelength, some distance from resonances. We measure transmitted energy and transverse width of the pulse and use schlieren imaging to probe the plasma column in the vapor close to the end of the vapor source. We find, that resonant pulses are more confined in a transverse direction by the interaction than off-resonant pulses are and that the plasma channels they create are more sharply bounded. Off-resonant pulses leave a wider layer of partially ionized atoms and thus lose more energy per unit propagation distance. Using experimental data, we estimate the energy required to generate a 20-meter-long plasma column and conclude that resonant pulses are much more suitable for creating a long, homogeneous plasma.