Generation of high-energy protons from the Coulomb explosion of hydrogen clusters by intense femtosecond laser pulses

Abstract

The energy distributions of protons emitted from the Coulomb explosion of hydrogen clusters by an intense femtosecond laser have been experimentally obtained. Ten thousand hydrogen clusters were exploded, emitting 8.1 keV protons under laser irradiation of intensity 6ϫ10 16 W/cm 2. The energy distributions are interpreted well by a spherical uniform cluster analytical model. The maximum energy of the emitted protons can be characterized by cluster size and laser intensity. The laser intensity scale for the maximum proton energy, given by a spherical cluster Coulomb-explosion model, is in fairly good agreement with the experimental results obtained at a laser intensity of 10 16-10 17 W/cm 2 and also when extrapolated with the results of threedimensional particle simulations at 10 20-10 21 W/cm 2 .

Scaling of Grating Spacing with Femtosecond Laser Fluence for Self-organized Periodic Structures on Metal

“…Even for a laser pulse with duration of 100 fs, the plasma wave moves only 0.9 μm. During this interval, an ion-enriched local area appears, and the ions experience strong Coulomb repulsion until the peak of the next electron wave arrives at that position, which can result in Coulomb explosion [49][50][51][52], thus giving rise to the formation of periodic grating structures. The depth of these gratings cannot be estimated in a straightforward manner within this interpretive framework.…”

“…We have proposed an interpretation of the observed LIPSS spacing, where we assume that LIPSS generation occurs through the following process: (1) plasma waves are induced on the surface by the femtosecond laser pulse; (2) spatially localized ion-rich areas Coulomb-exploded into vacuum [49,50], and consequently the thin layer is ablated and the interspaces of the gratings are printed during the first several pulses (the number of pulses depends on the laser energy fluence, and at certain high fluence values, only a single pulse is involved in this stage and the following one); and (3) the electric field is enhanced near the initially printed structures by subsequent pulses, and near-field light ablates the surface, thus deepening the grating structures [51][52][53]. When a plasma wave (electron wave) is driven in a bulk plasma by a laser pulse, the plasma wave dispersion is given by ω 2 = ω p 2 + 3/2v th 2 k 2 , where ω and k are the angular frequency and the wavenumber of the plasma wave, v th is the thermal speed of electrons in the plasma, and ω p is the plasma frequency.…”

Ion acceleration by intense, few-cycle laser pulses with nanodroplets

“…The condition stated by Sakabe et al 15 dimensionless amplitude a ¼ eE=mxc is a th % 6.3, which means that for I ¼ 5 Â 10 20 W/cm 2 the Coulomb regime should be entered. This transition is visible in Fig.…”

“…In Ref. 15, the regime of Coulomb explosion for hydrogen droplets has been studied in more detail, finding more intermediate energy spectra shapes for ions.…”

Formation mechanism of nanostructures in soda–lime glass using femtosecond laser

“…During the pulse duration of the femtosecond laser, the optical field ionization process is established and an ion-enriched local area is formed. The ions experience strong repulsive Coulomb force, due to the highly charge state of the molecules, until the subsequent electron wave peak appears at the same position, which causes Coulomb explosion [17]. As a consequence, periodic grating structures are printed on the substrate surface, which structures are oriented to the perpendicular direction of the laser polarization.…”