Hybrid CO₂-Ti:sapphire laser with tunable pulse duration for mid-infrared-pump terahertz-probe spectroscopy

We describe a mid-infrared pump - terahertz-probe setup based on a CO₂ laser seeded with 10.6 μm wavelength pulses from an optical parametric amplifier, itself pumped by a Ti:Al₂O₃ laser. The output of the seeded CO₂ laser produces high power pulses of nanosecond duration, which are synchronized to the femtosecond laser. These pulses can be tuned in pulse duration by slicing their front and back edges with semiconductor-plasma mirrors irradiated by replicas of the femtosecond seed laser pulses. Variable pulse lengths from 5 ps to 1.3 ns are achieved, and used in mid-infrared pump, terahertz-probe experiments with probe pulses generated and electro-optically sampled by the femtosecond laser.