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.
Highlights
Intense mid-infrared (MIR) and terahertz light pulses have enabled the discovery of unconventional phenomena such as the formation of magnetic polarization in antiferromagnets [1], ferroelectricity in paraelectrics [2,3], new topological phases [4], as well as non-equilibrium high Tc superconductivity in cuprates [5,6] and molecular organic materials [7,8,9,10]
Laser sources based on narrow band gap semiconductors, such as IV-VI compounds and wavelength tunable quantum cascade lasers produce radiation in the mid-infrared region of the electromagnetic spectrum (∼ 2.5 – 30 μm wavelength)
A pressure or electric field broadened spectral gain can support the amplification of picosecond CO2 laser pulses, it requires either an amplifier with a gas cell pressurized at 10 – 15 bar [21,22,23] or multi-stage preamplification for the generation of laser fields with intensities of more than 5 GW/cm2 [24]
Summary
Intense mid-infrared (MIR) and terahertz light pulses have enabled the discovery of unconventional phenomena such as the formation of magnetic polarization in antiferromagnets [1], ferroelectricity in paraelectrics [2,3], new topological phases [4], as well as non-equilibrium high Tc superconductivity in cuprates [5,6] and molecular organic materials [7,8,9,10] These experiments are performed using sub-picosecond pulses with high peak electric field (∼ 5 – 10 MV/cm). High peak power mid-infrared pulses are generated via optical parametric amplification and frequency mixing starting from ultra short light pulses generated by conventional solid state lasers (e.g. Ti:Al2O3 or Yb:YAG) This approach yields pulses with energies of 10 - 50 μJ and allows to reach MV/cm peak electric fields only for pulses with sub-picosecond durations. At 10.6 μm that are optically synchronized to the Ti:Al2O3 source, enabling experiments with sub-picosecond time resolution
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