Single-cycle powerful megawatt to gigawatt terahertz pulse radiated from a wavelength-scale plasma oscillator

We propose a scheme to generate single-cycle powerful terahertz (THz) pulses by ultrashort intense laser pulses obliquely incident on an underdense plasma slab of a few THz wavelengths in thickness. THz waves are radiated from a transient net current driven by the laser ponderomotive force in the plasma slab. Analysis and particle-in-cell simulations show that such a THz source is capable of providing power of megawatts to gigawatts, field strength of MV/cm–GV/cm, and broad tunability range, which is potentially useful for nonlinear and high-field THz science and applications.

Figure 1

(Color online) Schematic of THz emission from a plasma oscillator excited by a laser pulse obliquely incident on a few-wavelength uniform plasma slab. The plasma length is $L\sim {\lambda }_p$ and $\theta$ is the laser incident angle. THz waves are radiated in both specular reflection and transmission directions.

Figure 2

(Color online) Spatial-temporal plots of the electric fields $E_x$ (a), $E_y$ (b), and the pure THz magnetic field $B_z$ (c). The plasma is of density $n=0.0001n_c$ and length $L=100\lambda$ located in the $100\lambda \le x\le 200\lambda$ region. The laser pulse parameters are $a_0=0.5$, $d_L=100\lambda$, and $\theta =45°$.

Figure 3

(Color online) Peak field strengths ${\left|F_{\pm }\right|}_{\text{max}}$ of the THz pulses as a function of the plasma length $L$.

Figure 4

(Color online) (a) Temporal profiles of the THz waves $F_{+}$ for incident angles of $\theta =30°$, 45°, and 60°. (b) Temporal profiles of the THz waves $F_{-}$. (c) Power spectra (arb. units) of $F_{-}$ in (b). (d) Peak field strengths ${\left|F_{\pm }\right|}_{\text{max}}$ of the THz pulses as a function of $\text{sin}\theta$ with $\theta \in \left[0°,15°,30°,45°,60°,75°\right]$. 2D PIC results (see parameters in Sec. 4) are also included.

Figure 5

(Color online) (a) Peak field strengths ${\left|F_{\pm }\right|}_{\text{max}}$ of the THz pulses as a function of the laser intensity. We take $L=50\lambda$ and other parameters the same as in Fig. 2. (b) ${\left|F_{\pm }\right|}_{\text{max}}$ of the THz pulses as a function of the electron density $n$. The laser pulse parameters are $a_0=0.5$ and $\theta =45°$. For a given plasma density $n$, we always take $L=d_L={\lambda }_p$. The dashed lines are fitted curves.

Figure 6

(Color online) Conversion efficiency of THz emissions as a function of the laser intensity. All parameters are the same as in Fig. 5a.

Figure 7

(Color online) 2D spatial plot of the pure THz magnetic field $B_z$ for $w_L=10\lambda$ (a), $30\lambda$ (b), and $60\lambda$ (c) at the time $t=230\lambda /c$ in 2D PIC simulations. The dashed arrows present the THz emission directions, one along the laser propagation and the other along the specular reflection direction.

Figure 8

(Color online) Temporal profiles of the THz waves $F_{+}$ traced on the position $\left(x,y\right)=\left(200\lambda ,100\lambda \right)$ in 2D PIC simulations.

Figure 9

(Color online) Density profiles for uniform plasma $\left(u\right)$ with $L=50\lambda$ and nonuniform plasma $\left(n\right)$ with a trapezoidal profile. Linear slopes are $50\lambda$ long, and the whole nonuniform plasma length is $150\lambda$. The laser pulse parameters are the same as in Fig. 2.

Figure 10

(Color online) (a) Temporal profiles of the THz waves $F_{-}$ for uniform $\left(u\right)$ and nonuniform $\left(n\right)$ plasmas. (b) Temporal profiles of the THz waves $F_{+}$. (c) Power spectra (arb. units) of $F_{-}$ and $F_{+}$.