The Nonlinear Terahertz Spectroscopy Facility (NLTSF) consists of two main units:
(i) a multi-mJ femtosecond pump laser
(ii) the THz pump—THz probe (TP2) system. TP2 enables time-resolved studies of THz-induced phenomena by using a strong THz pulse to initiate changes in the sample and a weaker THz pulse to detect these.
The NLTSF is available for users.
Fig. 1. Scheme of the NLTSF.
Pump Laser. The THz sources of the system are driven by a cryogenically cooled Yb:CaF2 femtosecond pump laser with:
Central wavelength: 1030 nm
Pulse energy: 6 mJ
Repetition rate: 1 kHz
Pulse duration: 200 fs (sufficiently short to support the specified THz bandwidth 0.1–2.5 THz for the THz pump and for the THz probe).
The THz pump—THz probe (TP2) spectroscopy system. In the TP2 system, shown in Fig. 1, the optical pump pulse is split into 3 parts. The strongest part (typically 50–90% of the total energy) drives the source for the THz pump pulses. The generated single-cycle THz pulses of more than 10 μJ energy are tightly focused to achieve a peak electric field strength >/=450 kV/cm in the sample to be investigated.
Another part of the optical pump (typically 10–40% of the total energy) generates the THz probe pulses, which propagate through the sample collinearly with the THz pump. The sample can be cryogenically cooled down to 100 K. The remaining weakest part of the optical beam is used to provide the sampling pulses for electro-optic sampling (EOS). Behind the sample the waveform of the probe pulse is detected by EOS, which allows maximum information extraction from the measurement. Examples of measured waveform and spectra are shown in Fig. 2. The variable pump-probe delay enables time-resolved studies in the THz range of the processes induced by the strong THz pump pulse.
Specifications for the system are provided in tables below.
Table 1. Pump laser parameters.
Table 2. Pump THz parameters.
Table 3. Electro-optic sampling.
Table 4. Sample parameters.
Left panel: Temporal waveforms of THz pump and probe pulses measured by EOS. Right panel: Retrieved spectra of the THz pump and probe pulses.