Induction of subterahertz surface waves on a metal wire by intense laser interaction with a foil

We have demonstrated that a pulsed electromagnetic wave (Sommerfeld wave) of subterahertz frequency and 11-MV/m field strength can be induced on a metal wire by the interaction of an intense femtosecond laser pule with an adjacent metal foil at a laser intensity of $8.5\times {10}^{18}\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$. The polarity of the electric field of this surface wave is opposite to that obtained by the direct interaction of the laser with the wire. Numerical simulations suggest that an electromagnetic wave associated with electron emission from the foil induces the surface wave. A tungsten wire is placed normal to an aluminum foil with a gap so that the wire is not irradiated and damaged by the laser pulse, thus making it possible to generate surface waves on the wire repeatedly.

Figure 1

Experimental setup for the generation and measurement of the surface wave. An Al foil target is irradiated with intense laser pulses at an incident angle of 45°. The surface wave is detected at a distance of 180 mm from the thin film and a distance of 4 mm from the wire using an electro-optical effect.

Figure 2

(a) Typical waveform of the surface wave at various distances ($d=0.5$, 1, 2, 4 mm) between the foil and the wire. (b) Waveforms near the peak for various values of $d$ (0.1, 0.2, 0.3, 0.7, 1.5 mm).

Figure 3

Snapshots of the numerical simulation results. Electric field distributions along (a) the $y$ axis and (b) the $z$ axis, and (c) the electron distribution.

Figure 4

Experimental and simulated waveforms of the surface wave near the peak (normalized by the peak). The solid line is the simulation result and closed circles are experimental data.

Figure 5

Peak electric field of the surface wave on the wire for various distances between the foil and the wire. Assuming that the electric field is proportional to $1/r$, the experimental peak values are obtained by fitting the function $E\left(t\right)=\exp \left(-t/{\tau }_{\mathrm{decay}}\right)/\left[1+\exp \left(-t/{\tau }_{\mathrm{rise}}\right)\right]$ to the waveforms in Fig. 2. Open and closed circles indicate experimental and numerical results, respectively.