Tunable Few-Cycle and Multicycle Coherent Terahertz Radiation from Relativistic Electrons

We report the generation of tunable, narrow-band, few-cycle and multicycle coherent terahertz (THz) pulses from a temporally modulated relativistic electron beam. We demonstrate that the frequency of the THz radiation and the number of the oscillation cycles of the THz electric field can be tuned by changing the modulation period of the electron beam through a temporally shaped photocathode drive laser. The central frequency of the THz spectrum is tunable from $\sim 0.26$ to 2.6 THz with a bandwidth of $\sim 0.16\mathrm{THz}$.

Figure 1

Schematic of a linac-based light source for tunable THz generation and characterization.

Figure 2

Temporal profiles of the photocathode drive laser pulses for different time delays.

Figure 3

Measured longitudinal distribution (top row) and projected electron density distribution (bottom row) for a temporally modulated electron bunch.

Figure 4

Measured field autocorrelation of THz radiation for time delay $\tau =0.4\mathrm{ps}$ (a), 0.7 ps (b), 1.8 ps (c), and 3.6 ps (d).The spectra of THz radiation for time delay τ=0.4ps (a), 0.7ps (b), 1.8ps (c), and 3.6ps (d).

Figure 5

The spectra of THz radiation for time delay $\tau =0.4\mathrm{ps}$ (a), 0.7 ps (b), 1.8 ps (c), and 3.6 ps (d).

Figure 6

Variation of THz frequency as a function of time delay $\tau$.

Figure 7

THz pulse energy as a function of radiation frequency.