Application Description

THz time-domain spectroscopy is used to characterize material properties by measuring the complex frequency response within the frequency range from 0.1 THz to tens of THz. In this regime it is possible to observe various fundamental resonances, such as electronic and phononic excitations in solid-state materials.

To measure the complex frequency response of a material, a THz transient with tailored spectrum is generated by an ultrashort pump pulse in a non-linear process. The interaction with the sample modifies the transient, which is then either reflected or transmitted. The resulting waveform is detected by an ultrashort probe pulse using a non-linear technique based on electro-optic sampling or photoconductive antennas, for example, so that its instantaneous electric field is revealed. The time delay between the probe pulse and the THz field is varied to enable the full reconstruction of the waveform in amplitude and phase of the electromagnetic field. Similarly to other ultrafast optical techniques, e.g. pump-probe spectroscopy, the temporal resolution is given by the duration of the probe laser pulse and not by the bandwidth of the photodetectors or the measurement electronics. This means that THz time-domain spectroscopy can uncover changes on the THz wave packet with sub-cycle temporal resolution.