Intense circularly polarized attosecond pulse generation from solid targets irradiated with a two-color linearly polarized laser

A method for the production of intense circularly polarized (CP) attosecond pulses from relativistic laser-solid interactions is proposed, where a two-color linearly polarized (LP) laser is used. The polarization, photon frequency, and other properties of the obtained attosecond pulse can be controlled by adjusting the ratio of the dichromatic driving LP field in different harmonics, which is much easier and more efficient than those previously using CP driving lasers. Both one- and two-dimensional particle-in-cell simulations show that a CP attosecond extreme-ultraviolet pulse with an intensity of $1.4\times {10}^{19}\mathrm{W}/{\mathrm{cm}}^2$ and a duration of about 120 as is obtained by a two-color LP laser at intensities in the fundamental and second harmonics of, respectively, $1.5\times {10}^{22}$ and $6.4\times {10}^{21}\mathrm{W}/{\mathrm{cm}}^2$, which can be applied for the detection of the magnetic and chiral properties of materials.

Figure 1

(a) Schematic for the principle of the proposed scheme: generation of CP attosecond pulse from solid targets by an intense two-color LP laser via ROM. (b) Waveform of the obtained CP attosecond XUV pulse after spectral filtering in 1D PIC simulation, where the 30th–46th harmonic orders are selected. The waveform of the 3D electric field vector (black) and the two orthogonal electric field components $E_y$ (blue, light gray) and $E_z$ (red, dark gray) are displayed. The laser and target parameters in the simulation are described in the text.

Figure 2

1D PIC simulation results for the proposed scheme, where the simulation parameters are shown in the text. (a) Spatiotemporal distribution of the electron density $n_e$ and (b) time derivations of the current density $\partial J/\partial t$. The inset of panel (a) shows the electron density $n_e$ along the surface in one-color (blue, light gray) and two-color (red, dark gray) laser cases, respectively, where arrows indicate the location of the mirror surface. The inset of panel (b) shows $\partial J/\partial t$ of the one-color case. (c) and (d) The obtained harmonic spectra in the specular direction at $t=96T_0$ for the two- and one-color laser cases, respectively. (e) and (f) The normalized field intensities $|E_y{|}^2$ (upper panel) and $|E_z{|}^2$ (lower panel) of the attosecond pulse after selecting 30th–46th harmonic orders emitted around the peak laser intensity for the two- and one-color laser cases, respectively.

Figure 3

One-dimensional PIC simulation results for a wide range of laser parameters including intensities $I$, incident angles $\theta$, and intensity ratios of the two-color field $W$. Panels (a) and (b) show dependencies of, respectively, the phase difference $\mathrm{\Delta }{\varphi }_{\mathrm{rad}}$ and the ellipticity $\epsilon$ of the obtained attosecond pulse after spectral filtering on laser intensities $I$ as well as intensity ratios $W$. Panels (c) and (d) show those dependencies on the incident angles $\theta$ as well as $W$. (e) $\mathrm{\Delta }{\varphi }_{\mathrm{rad}}$ in two orthogonal directions with harmonics 10th–20th (blue triangles, light gray) and 30th–46th (red squares, dark gray) depending on the initial phase ${\varphi }_0$ of the two-color laser, where $I=2.14\times {10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ and $W=0.3$ are taken. (f) Wave form of the obtained CP attosecond XUV pulse after spectral filtering with 15th–20th harmonics, where lower intensities of $I=8.55\times {10}^{18}\mathrm{W}/{\mathrm{cm}}^2$ and $W=0.3$ are taken.

Figure 4

Two-dimensional PIC simulation results. (a) Spatial distribution of the electric fields $E_z$ and $E_x$ of the obtained attosecond pulses after spectral filtering (selecting 30th–46th harmonic orders) and wave form of the 3D electric field vector (red) along the $Y$ axis. (b) and (c) The corresponding high harmonic spectra in two directions. (d) Current densities of the oscillating plasma surface.