Tunable ultrabroadband hybrid terahertz emitter combining a spintronic and a GaSe source

We introduce a hybrid THz-source concept based on a spintronic THz emitter (STE) deposited onto a thin free-standing GaSe nonlinear crystal. By tuning the magnetic state and the phase-matching parameters of the hybrid emitter, we generate an ultrabroadband spectrum covering the full range from 1 to 40 THz. We achieve significantly enhanced spectral amplitudes above 10 THz compared to the bare STE, resulting in ultrashort THz-pulse durations down to 32 fs. Finally, we demonstrate the straightforward tunability of the shape of the few-cycle pulse from symmetric to antisymmetric.