Fyzikální ústav Akademie věd ČR

Terahertz (THz) radiation lies in the frequency range between the infrared and microwaves, i.e. between 100 GHz and 10 THz. These waves are able to excite soft polar phonons in solids, vibrations of larger chains in biomolecules, to induce plasma oscillations of free charge carriers with concentrations of ~10¹⁴–10¹⁸ cm^-3 and to interact with carriers localized in nanoparticles. Due to the lack of bright sources and sensitive detectors the THz spectroscopic applications about 20 years ago concerned mainly the astronomy and analytical science. Recent technological innovations in photonics and nanotechnology have lead to a dramatic increase in the interest of the scientific and industrial community in the THz research and applications.

We use an optoelectronic approach to the generation and detection of broadband THz pulses which makes use of ultrashort optical pulses and of their frequency conversion into the THz range. This technique is called the time domain THz spectroscopy and it is able to measure complex dielectric and conductivity spectra of various kinds of samples in a spectral range of 5 to 80 cm^-1. In addition, the use of laser pulses for the THz generation makes it possible to perform so called pump–probe experiments where the sample is first excited by an optical (UV, VIS, IR) pulse and, subsequently, it is probed by a delayed THz pulse. This technique allows us to access the far-infrared fingerprints of the ultrafast dynamics on sub-picosecond to nanosecond time scales.

(More information on the website of the THz group.)

Research Activities

• THz spectroscopy of ferroelectrics and related materials (bulk, thin films); with the emphasis on tunable THz applications
• photonic crystals and metamaterials for the THz range
• ultrafast photoconductivity in semiconductors and molecular systems
• THz near-field microscopy

Equipment

• Ultrafast lasers and amplifiers
  • MIRA seed femtosecond oscillator (Coherent)
  • VITESSE femtosecond oscillator (Coherent)
  • ODIN multipass femtosecond amplifier (Quantronix)
  • TOPAS parametric amplifier (Light conversion)
• Custom-made THz time-domain spectrometer placed in a vacuum chamber; suitable for optical pump – THz probe experiments
• Cryostat and furnace with suitable windows accepting both optical and THz beams (available temperature range: 10–900 K)
• Custom-made THz near-field spectrometer