Optical waveform synthesis and applications

Example: THz generation in plasmas

The generation of THz waves in plasmas opens a straightforward flexible way of producing powerful and broadband THz sources with modest energy and pulse-duration requirements on the pump source. In our project we concentrate on the generation of broadband THz radiation in laser induced plasmas using the two color w, 2w intermixing scheme (Fig. 1). In addition, filaments are explored as a mean of producing and guiding of the THz pulses.

Figure 1 Two color scheme for the THz generation.

The generation of terahertz emission is related to the asymmetric electron drift current. Symmetry of the electron tunneling is broken using coherent superposition of first and second harmonic fields which leads to a directional electron drift as shown in Figure 2. In the spectrum of the current one can see a low frequency peak (in the THz range)  when two color field is used.

Figure 2. Simulation of THz pulse emission. a) the electric field of superimposed first and second harmonic (blue) and corresponding time-dependent electron current (green). b) Power spectrum of the generated electron current in case of single color and two-color pulses.

Experimentally pulses are measured using the electrooptical (EO) detection. An example of the measured time-dependent electric fiend and its spectrum is shown in Figure 3.

Figure 3 Typical THz transient obtained using the two color scheme and the corresponding spectrum shown in the inset.

Last update Nov. 4, 2009