High-energy sub-picosecond pulse generation from 3 to 20 μm

We have produced sub-picosecond pulses in the wavelength range 3-20 mum with energies as high as 2 muJ, through difference-frequency mixing in the crystal GaSe. Input beams for the non-linear mixing process came from either a regenerative amplifier operating in two-color mode, due to the spectral shaping of its injection beam, or an optical parametric amplifier (OPA). The first method was straightforward to implement and provided easy access to the wavelength range 10-20 mum. The intermediate OPA stage, though technically more involved, allowed higher input beam irradiances and resulted in shorter duration MIR pulses, greater conversion efficiency and access to the MIR region between 3 and 10 mum.