Ultrafast high-resolution THz time-domain spectroscopy

Ultrafast time-domain spectroscopy based on free induction decay radiation of molecules excited by NovoFEL THz pulses is described. The radiation was detected by ultrafast Schottky diode detectors with a rise time shorter than 20 ps. The highest spectral resolution of the method is limited by the lowest repetition frequency of NovoFEL pulses, which constitutes 5.6 MHz. Routine spectral measurements can be made for a time of one nanosecond. The technique can be used to study ultrafast nonrepeatable phenomena. Another application is a spectral “cinema” with a picture frequency of up to 22.5 MHz.