  Linear terahertz time-domain spectroscopy (THz-TDS) is a sensitive probe for
material characterization including thickness measurements of thin layers.
These applications critically rely on a sufficiently large bandwidth, which is
not straightforwardly available in typical THz-TDS systems. Here, we introduce
a hybrid THz-emitter concept based on a spintronic THz emitter that is
deposited onto a thin freestanding GaSe nonlinear crystal. By tuning the
parameters of this hybrid emitter, we generate an ultrabroadband spectrum
covering the full range from 1 to 40 THz without any gaps at high spectral
amplitudes, resulting in ultrashort THz-pulse durations of only 32 fs. Finally,
we demonstrate the straightforward tunability of the carrier-envelope phase
from unipolar or bipolar THz pulses with ultrashort duration.
