Photo-Electronic Characterization of Carbon Nanotubes for Near-Critical Density Applications

Laser wakefield acceleration (LWFA), first proposed in 1979 by Tajima and Dawson [1], represents a promising path toward remarkably compact particle accelerators. Extending LWFA to the near-critical density (NCD) regime is a key goal for further miniaturization, necessitating the use of structured materials [2, 3]. Among these, carbon nanotube (CNT) arrays are a leading candidate due to their highly porous structure, which allows for a tunable effective electron density ideal for creating compact, solid-state accelerator targets [4]. However, a fundamental understanding of the electronic response of these arrays—specifically how light absorption and charge generation efficiencies depend on laser parameters in the NCD regime—remains incomplete.

This work provides a foundational characterization of the photo-electronic response of these materials using ultrashort (< 120-fs) laser pulses. To establish a baseline understanding, we investigate the photocurrent generated from the CNTs as a function of excitation wavelength. This characterization is performed in a low-intensity regime to avoid sample damage, allowing for repeatable measurements of the material’s intrinsic photo-absorption properties as the laser frequency approaches the condition for near-critical density. We also utilize laser polarization to probe the anisotropic response, adding insight into how the electric field and nanotube alignment governs the laser-matter interaction. This foundational dataset is a critical prerequisite for future design of higher-intensity LWFA experiments with NCD structured targets.

References:

[1] T. Tajima and J. M. Dawson, Phys. Rev. Lett. 43, 267 (1979);

[2] Michiaki Mori, et al. AIP Advances 14, 035153 (2024);

[3] E. Barraza-Valdez, et al. Photonics 9, 476 (2022);

[4] B. S. Nicks et al., Photonics 8, 216 (2021).