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Abstract:

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.

Abstract:

Recent advances in laser technology have made possible the generation of precisely shaped strong-field pulses at terahertz frequencies. These pulses are especially useful to selectively drive collective modes of solids, for example exciting the lattice to very large amplitudes. One can consider different types of lattice excitations, including rectification and high-order harmonics. Here, I discuss the fundamentals of the coherent control of the lattice. I also show how lattice excitation can be used to switch the electronic and magnetic phases of solids. I discuss experiments in which lattice excitation drives changes in the conductivity or enhancement in superconductivity.