The Novosibirsk Free Electron Laser (NovoFEL) is a powerful source of narrow-band terahertz and infrared radiation, operating at the Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences (INP SB RAS). It is based on an accelerator-recuperator system and is one of the main user facilities of the Siberian Synchrotron and Terahertz Radiation Center. In recent years, there has been active work to develop new diagnostics for measuring the parameters of the electron beam in the third stage of the NovoFEL. The laser generates pulses of radiation with picosecond durations in the mid-infrared range of 8-12 micrometers that is the challenge for the diagnostics. This paper describes the development of diagnostic systems for the spectral and temporal characteristics of laser radiation from the third stage of the NovoFEL facility. To record the radiation spectra, a diffraction monochromator was used in conjunction with a bolometric array as a detector. A nonlinear autocorrelator based on ZnGeP2 crystal was developed to measure the temporal profile of the radiation. The correct operation of the autocorrelator was demonstrated in experiments with YAG laser radiation acquired using a nonlinear β-BaB2O4 crystal. The paper presents results from measurements of the spectrum and autocorrelation function for laser radiation from the third stage of the NovoFEL. Self-consistency between the spectrum and autocorrelation functions is demonstrated.

The Novosibirsk Free Electron Laser (NovoFEL) facility consists of three free electron lasers (FELs) installed on different tracks of the Energy Recovery Linac (ERL). These FELs share a common acceleration system, which allows for the generation of high average electron currents, typically around 10 mА. This high current facilitates the production of significant average FEL powers, often exceeding 100 watts in the spectral range between THz and mid-infrared wavelengths. Precise measurement of electron beam parameters is crucial for monitoring the performance of the accelerator and fine-tuning its operating modes. The length of the electron bunch is particularly important, as it directly influences the efficiency of laser radiation generation. This study focuses on the dependence of the electron bunch length on the parameters of the radio frequency (RF) and bunching systems for the first and second FELs at NovoFEL. Measurements were conducted using a Cherenkov aerogel radiator in conjunction with a streak camera to accurately determine the electron beam properties. The measurement results, along with a plan for future experiments, are discussed in detail in this publication.