Ultrafast Techniques

THz generation & detection

We use a nonlinear process called optical rectification to generate THz pulses. The terahertz pulses are generated via optical rectification in a nonlinear crystal using femtosecond near-infrared pulses. For detection, the terahertz pulses overlap with near-infrared pulses in another nonlinear crystal. Due to the electro-optic effect, the polarization of the near-infrared pulses rotates according to the strength of the terahertz pulses. By scanning the delay of the near-infrared pulses, both the magnitude and phase of electric field of the terahertz pulses can be recorded. By compariing the complex transmission coefficient with and without passing through a sample, the complex value of the material parameters such as refractive index or dielectric constant in terahertz ranges can be measured.