Generation and field-resolved detection of femtosecond electromagnetic pulses tunable up to 41 THz

Bandwidth-limited infrared pulses as short as 50 fs are generated in thin GaSe crystals by phase-matched optical rectification of 10 fs laser pulses. The central frequency of the transients is continuously tunable over a wide interval extending from 41 THz $\text{(λ=7\hspace{0.05em}μ}\mathrm{m})$ to the far-infrared. The electric field of the THz transients is directly monitored via ultrabroadband free-space electro-optic sampling. A simulation of the spectra based on a plane-wave model shows excellent agreement with the experiment.