Unlike synchrotrons with multiple beamlines, free electron lasers (FELs) are single-beam facilities, which nevertheless have a number of endstations. The latter requires development of complex radiation transport line, which should be efficient enough to avoid scaling down the FEL capabilities. Keeping the beam shape and radiation power level along the beamline is a challenge because the total length of the FEL radiation transport line can exceed a hundred meters. The FELs around the world differs each other in both radiation parameters and endstations layout requiring individual design of their radiation transport lines. In this work we describe the 120-m beamline for transporting the radiation of the Novosibirsk free electron laser facility (NovoFEL), consisting of three FELs of the terahertz (THz), far-infrared, and mid-infrared ranges. The radiation of these three FELs is directed to the same beam transport channel, which is able to deliver the radiation to any of 14 endstations already commissioned. To compare the expected beam parameters with the actual ones, the radiation intensity distribution was measured in a number of places of the beamline that are THz radiation outputs for some endstations. Possible causes of the parameters mismatching observed for distant endstations are discussed. The problem of radiation absorption by water vapor is considered in detail.

Diffraction of terahertz radiation on ultrasound in liquefied sulfur hexafluoride at room temperature was observed for the first time. The dependences of the diffraction efficiency on the sound frequency, angle of incidence, and amplitude of radio-frequency electrical signal applied to a piezo-transducer were studied. Deflection of diffracted radiation by an angle of 10°was observed. It was found that the diffraction efficiency at room temperature is significantly (four times) higher than the one at 14°C known from the literature. The obtained and published data on the acousto-optic diffraction in liquefied sulfur hexafluoride contradict the well-known theory.

As areas of application of terahertz (THz) radiation expand in science and practice, evidence is accumulating that this type of radiation can affect not only biological molecules directly, but also cellular processes as a whole. In this study, the transcriptome in cells of the thermophilic bacterium Geobacillus icigianus was analyzed immediately after THz irradiation (0.23 W/cm², 130 μm, 15 min) and at 10 min after its completion. THz irradiation does not affect the activity of heat shock protein genes and diminishes the activity of genes whose products are involved in peptidoglycan recycling, participate in redox reactions, and protect DNA and proteins from damage, including genes of chaperone protein ClpB and of DNA repair protein RadA, as well as genes of catalase and kinase McsB. Gene systems responsible for the homeostasis of transition metals (copper, iron, and zinc) proved to be the most sensitive to THz irradiation; downregulation of these systems increased significantly 10 min after the end of the irradiation. It was also hypothesized that some negative effects of THz radiation on metabolism in G. icigianus cells are related to disturbances in activities of gene systems controlled by metal-sensitive transcription factors.