A fiber-optic setup incorporating the pump-probe thermoreflectance (TR) technique with Fabry-Perot (FP) interferometer is presented. It includes both heat pump and probe lasers, producing wavelengths of 1470 and 1530 nm, respectively, together with a reflected radiation detector. Heat pump pulse duration varies from a few microseconds to tens of microseconds. The potential of the pump-probe TR-FP technique to investigate the subsurface region of semiconductors with a range of electron spectra is demonstrated. A pronounced dip in time dependence of the TR-FP signal is discovered at the liquid nitrogen temperature in the gapless semiconductor compound HgSe-a candidate for the family of Weyl semimetals with broken inversion symmetry. This finding implies the developed pulsed TR-FP method for the detection of Weyl nodes and surface Fermi arcs in solids.

A study of the reflection of infrared radiation at a wavelength of 1530 nm from the surface of HgSe single crystals in a two-beam pump-probe fiber-optic scheme was carried out using the thermoreflectometry (TR) method with a Fabry-Perot interferometer (FP). Along with the "high-temperature" anomaly of the probe laser signal (at T > 100 K) in the relaxation region, a "low-temperature" anomaly was revealed in the heating region, consisting in a change in signal polarity at T < 50 K. A qualitative interpretation of the observed features of the relative intensity of the reflected signal in the region of heating and relaxation is proposed, based on the hypothesis of two types of energy barriers, separating the bulk chiral states from the Fermi-arc surface states. Keywords: thermal reflection, interferometer, mercury selenide, Weyl nodes.