Enhancement of Kα emission through efficient hot electron generation in carbon nanotubes on intense laser pulse irradiation

Abstract

Conversion efficiency and spectral broadening of the K-α line emitted from planar titanium targets irradiated with ultra-short laser pulses of high intensity Near complete absorption of the energy of intense ultra-short laser pulses (45 fs, intensity $1.6 Â 10 16 to 2.5 Â 10 17 W/cm 2 ) is observed in carbon nanotubes deposited on a planar molybdenum substrate. The hollow structure of the nanotube plasma facilitates resonant electric field enhancement during its ionization phase. This resonantly enhanced localized field at a density much larger than the critical density n c leads to efficient hot electron generation, which results in enhanced K a emission of Mo at 17.5 keV. It is observed that for nanotubes, depending on the degree of hollowness, there is an optimum laser intensity for maximum x-ray enhancement compared to a planar uncoated target.

Investigation on laser–plasma coupling in intense, ultrashort irradiation of a nanostructured silicon target

“…The experimental results show that nanostructured targets have a preplasma threshold lower at least by a factor 3 (we did not investigate laser intensities lower than ∼10 17 W µm 2 cm −2 ), which confirms that their absorptivity is significantly larger than that of flat targets. The larger absorptivity could be due to the volumetric heating of the target [22], to the rebounds of lights between the structures or to the enhancement of electric fields in the surface cavities [2,20]. The lower lateral heat conduction can also contribute to this result.…”

“…The mechanisms able to produce an enhancement of the absorptivity of a nanoor micro-structured target can be various, depending on the geometry and dimensions of the structures. This includes the enhancement of the local electric field due to the 'lightning rod' effect at the tip of nanocolumns or to the presence of Mie plasmonic resonances in the absorption spectrum [1,2,7,[9][10][11][17][18][19], the enhancement of local fields or the multi-reflections in the target cavities [2,20] and the reduced lateral heat conduction into the target [21]. An interesting effect, resulting from the irradiation of a nanowires target with an ultrashort pulse, is that the absorption becomes volumetric rather than restricted at the material skin depth or at the critical density surface, producing an ultrahot dense plasma [22].…”

Transition from Coherent to Stochastic electron heating in ultrashort relativistic laser interaction with structured targets

“… 15 , then showed a significant enhancement of X-ray emission by using nanostructured surfaces. Since then several target geometries have been tested both in experiments and in numerical simulations, in a wide range of laser intensities from 10 14 to 10 22 W/cm 2 , including wires/nano-brush 4 , 6 , 11 , 12 , nano-spheres 2 , 16 , gratings 17 , nano-holes 18 , nano/microtubes 3 , 7 . However, in spite of the considerable amount of experimental data, a satisfactory knowledge of the key control parameters is still missing, thereby limiting the exploitation of this class of targets for applications.…”

Hot electrons injection in carbon nanotubes under the influence of quasi-static ac-field

“…Hot electron phenomena have become important for the understanding of all modern semiconductor devices [26]- [27]. There are several reports on hot electrons generation in CNTs [28]- [30], but the reports on hot electrons injection in CNTs under the influence of quasi-static ac field to the best of our knowlege are limited.…”