Study of single-crystal and polymer pyroelectric detectors in the 0.9–2.0 THz range using the Novosibirsk FEL

The development of efficient and reliable detectors operating at room temperature is essential for the advance of science and technology that rely on terahertz (THz) radiation. Pyroelectric THz detectors are among the best candidates, given their variety, excellent technical characteristics, ease of fabrication and reliability. In this work we compare six different detectors based either on a LaTiO₃ crystal or on various polymer films, using monochromatic radiation of the Novosibirsk free electron laser in the 0.9–2.0 THz frequency range. Their main characteristics were determined for all detectors, including the noise equivalent power and the frequency dependence of the response. Possible reasons for the differences between the characteristics obtained are discussed on the basis of the physicochemical and optical properties of the sensitive area. Three detectors showed sufficient sensitivity to record the shape and duration of THz macropulses using only a small fraction of the THz radiation from the main beam. This makes it possible to characterise the parameters of THz radiation accurately in parallel with the main experiment at various specialised user endstations at synchrotrons and free electron lasers. As an example of such characterisation, the stability of the average power of the Novosibirsk FEL was studied at the electron paramagnetic resonance (EPR) spectroscopy endstation.

In addition, a compact detector based on a polyvinylidene difluoride pyroelectric film coated with sputtered metal electrodes was fabricated to measure the THz absorption of the sample under study in situ at cryogenic temperature. The detector design was optimised for the detection system of the EPR spectroscopy endstation. The applicability of such a detector to in situ absorption measurements was demonstrated on two typical molecular spin systems with a transparency of 20–25% at 76.9 cm⁻¹ and 4 K. Measurements of this kind, carried out directly inside the cryostat with the main detection system and the sample fully tuned, allow accurate control over the parameters of the THz radiation used in the experiment.

This work was supported by the Russian Science Foundation 23-73-00042.