The design and operational characteristics of the Novosibirsk free electron laser facility are described. Selected experiments in the terahertz range carried out recently at the user stations are surveyed in brief.

We study diffraction of Bessel vortex beams with topological charges of ±1 and ±2 and a wavelength of 130 µm on two-dimensional amplitude periodic gratings. Results of simulations and experiments at the Novosibirsk Free Electron Laser facility show that there appear periodic patterns in the planes corresponding to the classical main and fractional Talbot planes, but instead of self-images of the holes, there are observed periodic lattices of annular vortex microbeams with topological charges corresponding to the charge of the beam illuminating the grating. The ring diameters are the same for beams with different topological charges, but they are proportional to the grating period and inversely proportional to the diameter of the beam illuminating the grating.

In-line holography systems have been designed and investigated using Novosibirsk free electron laser as a source of monochromatic tunable terahertz (THz) radiation. A thermograph, a thermal sensitive phosphor plate, and a microbolometer array were applied to recording of holograms in the spectral ranges of 128-160 m and 68 m, including recording in real time. Specific features of these devices are described in detail. Five methods of image reconstruction are analyzed and verified using recorded holograms. Prospects for the use of THz holography are discussed in brief.

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The Talbot effect in the terahertz spectral range has been first observed and used in metrology applications: measurement of distance, determination of radiation wavelength, and real-time detection of wavefront distortion.

Gradually appearing high-power terahertz sources require the development of adequate imaging techniques. This paper describes four imaging techniques (with a thermal recorder, temperature-sensitive phosphor plates, a visible-light thermal sensitive Fizeau interferometer, and an uncooled microbolometer array) applied with the Novosibirsk terahertz free electron laser as a radiation source. The space and time resolutions of the devices were examined thoroughly. Examples of the application of these techniques, including in-line holography and real-time moving-objects detection, are given.