Absorption of femtosecond laser pulses in high-density plasma

Abstract

The absorption of 250-fs KrF laser pulses incident on solid targets of aluminum and gold has been measured as a function of polarization and angle of incidence for the intensity range of 10' -2.5x10" Wcm . Maximum absorption of over 60% occurs for p-polarized radiation at angles of incidence in the range of 48'-57'. The measured results are in agreement with absorption on a steep density gradient.

Transient EUV Reflectivity Measurements of Carbon upon Ultrafast Laser Heating

“…On the other hand, the short wavelength of EUV photons, as compared to optical ones, enhances the sensitivity of transient EUV reflectivity to surface displacements, which reflects the dynamics of the lattice [21]. An expanding surface can indeed introduce a dependence of τ on λ probe [11,22,23], which is compatible with the weak dependence of τ on λ probe observed in our experiment (see Figure 3); unfortunately, the large scattering of the present data does not allow the analysis of the wavelength dependence to be pushed beyond a mere qualitative comparison. Further and more accurate data are definitely needed to improve data interpretation.…”

Role of surface roughness in hard-x-ray emission from femtosecond-laser-produced copper plasmas

“…In the case of a p-polarized laser beam, it is well known that in experimental conditions similar to ours, the hot electrons could be generated by two mechanisms -resonance absorption (RA) and vacuum heating (VH). RA has been well studied both experimentally [17,18,19,20] and theoretically [21,22,23,24] and based on the observations and simulations, the following scaling law [21] has been established:…”

Short-Pulse Laser-Produced Plasmas

“…Figure 2 shows the absorption coefficient as a function of the incidence angle for different plasma scale length L calculated with a model of laser-plasma interaction with a grating target [33]. We find a good qualitative agreement, both in incidence angle position and absorption fraction (see Fig.2a), between the crude model and more involved calculations [20,21] with a flat target. In particular, the fact that the absorption maximum is displaced towards grazing angles for steep electron density gradients is in accord with more elaborate calculations of resonance absorption [15].…”

“…It is crucial to obtain a time-and space-resolved picture of the very steep gradient around the critical density region to study the laser absorption mechanisms. Indeed, most of the energy transfer between the laser and the solid target occurs [19][20][21] in plasma regions where 0.5n c < n e < 10n c where n c is the critical density. With lasers of ≈100-fs duration, hydrodynamic simulations (see Sect.5) show that the gradient scale length L can be very much smaller than the laser wavelength λ and that typical expansion velocities are in the 0.1-nm/fs range.…”