We demonstrate the possibility of broadband THz pulse generation in mixed GaSe1−xSx and GaSe1−xTex crystals. The ordinary and extraordinary refractive indices of the crystals have been measured by the terahertz time-domain spectroscopy method, those values strongly influence the efficiency of THz generation process. The high birefringence and transparency of pure GaSe and mixed crystals allow optical rectification of femtosecond laser pulses in the several millimeters thick crystal using the еее interaction process (with two pumping waves and generated THz wave all having extraordinary polarization in the crystal).

We demonstrate the generation of mid-infrared radiation using a femtosecond dual-signal-wavelength optical parametric oscillator and difference frequency generation in an extracavity gallium selenide or silver gallium diselenide crystal. This system generates up to 4.3 mW of average mid-infrared power. Its spectra can be tuned to between 10.5 μm and 16.5 μm wavelength ($952{\mathrm{cm}}^{-1}–606{\mathrm{cm}}^{-1}$) with more than $50{\mathrm{cm}}^{-1}$ spectral bandwidth. We demonstrate that the power and spectra of this system are temporally very stable.