FEL & Utilization Section

Development of facilities for terahertz-infrared (IR-THz) spectroscopy

Within the second stage of the three stage program on FELs, the FUS is building a set-up for doing experiments using the FEL as well as laboratory based (infrared-terahertz) sources in low temperature (5-300 K) and high magnetic field (up to 7 T) sample environment. Fig. 1 shows a picture of a set-up for doing frequency domain spectroscopy of materials. The set-up is compatible with the present IR-FEL (200- 800 cm-1), and also has its own sources: Hg Arc Lamp (2- 600 cm-1), Globar (50- 2000 cm-1).
The set-up is equipped with the following detectors: Cryogen free In-Sb Hot Electron Bolometer (2- 40 cm-1), Cryogen free Nb-TES Bolometer (10- 600 cm-1), Liquid N2 cooled Mercury-Cadmium Telluride (MCT, 600- 2000 cm-1), and Deuterated L-Alanine doped Triglycine Sulphate (DTGS, 10– 2000 cm-1)

Figure 1: A picture of the frequency domain spectroscopy set-up for doing experiments using FEL and laboratory based sources.
Figure 1: A picture of the frequency domain spectroscopy set-up for doing experiments using FEL and laboratory based sources


Another experimental facility has been established for doing terahertz time domain spectroscopy (THz-TDS) including pump-probe experiments in low temperature (5-300 K) and high magnetic field (up to 7 T) sample environment. Fig. 2 shows a picture of the set-up for THz-TDS and pump-probe experiments. The salient features of this experimental set-up are:
  1. Spectral range: 0.1– 3 THz (~4–99 cm-1)
  2. Pulse duration: ~10 ps
  3. THz Power: ~2 μW
  4. Terahertz generation and detection: Using (Ga,Bi)As based Photoconductive Antenna, with integrated collimating lens (high resistivity Si).
  5. Laser: Diode pumped solid state (DPSS) laser with central wavelength 1030 nm, pulse duration 96 fs, and repetition rate of 76 MHz.
Using this facility (THz-TDS, near-infrared pump & terahertz probe), useful physical properties like optical conductivity, charge carrier dynamics etc. can be studied as a function of temperature, magnetic field, and frequency in the transmission and reflection modes.

Figure 2: A picture of the set-up for doing THz-TDS and pump-probe experiments
Figure 2: A picture of the set-up for doing THz-TDS and pump-probe experiments
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