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A system for diagnostics of the electron-beam position in the channel of the microtron–recuperator (MR) of the Novosibirsk free-electron laser is described. The position of the beam is measured using electrostatic BPM stations that are installed in different parts of the vacuum chamber on the path of the beam along the accelerator channel. The features of the operation of the multiturn MR resulted in the necessity to develop an algorithm for measuring the beam position that differs from the algorithms that are used on other charged-particle accelerators. This system can be used to measure the positions separately of both accelerated and decelerated beams that are simultaneously present in some segments of the MR.

The Novosibirsk FEL facility has three FELs installed on the first, second, and fourth orbits of the multiturn energy recovery linac (ERL). The first FEL covers the 90–240 μm range of wavelengths at an average radiation power of 0.5 kW with a pulse repetition rate of 5.6 or 11.2 MHz and a peak power of 1 MW. The second FEL operates in the 40–80 μm range of wavelengths at an average radiation power of 0.5 kW with a pulse-repetition rate of 7.5 MHz and a peak power of around 1 MW. These two FELs are the world’s most powerful (in terms of average power) sources of coherent narrow-band (less than 1%) radiation in their wavelength ranges. The third FEL was commissioned in 2015 to cover the 5–20 μm range of wavelengths. The Novosibirsk ERL is the world’s first and only multiturn ERL. Its distinctive features include a normally-conductive 180 MHz accelerating system, a direct current (DC) electrostatic electron gun with a control grid and thermionic cathode, three operating modes of the magnetic system, and a compact (6 × 40 m) design. The Novosibirsk FEL facility has been in operation for users of terahertz radiation since 2004.

A new variable period undulator of unique design was developed and built recently at Budker INP. It will replace the electromagnetic undulator in use now on the second FEL of the Novosibirsk FEL facility. As a result, the FEL tunability range will be substantially extended. In this paper, we present the results of measurements of the undulator magnetic field for different periods and discuss ways to reduce the field errors, which include sorting of magnets, weakening of undulator edge poles, and using of steering coils.

The Novosibirsk FEL facility includes three FELs operating in the terahertz, far-, and mid- infrared spectral ranges. It has rather long history, but its potential has not been fully revealed so far. The first FEL of this facility has been operating for users of terahertz radiation since 2004. It remains the world's most powerful sources of coherent narrow- band radiation in its wavelength range (90 – 340 µm). The second FEL was commissioned in 2009. Now it operates in the range of 35 – 80 µm, but we plan to replace its undulator soon with a new one, and its short wavelength boundary will be shifted down to 15 µm. The third FEL was commissioned in 2015 to cover the wavelength range of 5 – 20 µm. Its undulator comprises three separate sections. Such lattice is suited very well to demonstrate the new off-mirror way of radiation outcoupling in an FEL oscillator (so called electron outcoupling), which we also plan for near future. We also intend to improve the accelerator injection system. As a result, the average electron beam current and consequently the radiation power of all the three FELs will increase. In this paper, we present an overview of the facility and discuss our recent achievements and future plans.

Novosibirsk FEL facility is based on the first in the world multi-turn energy recovery linac (ERL). It comprises three FELs (stages). FELs on the first and the second tracks were commissioned in 2004 and 2009 respectively and operate for users now. The third stage FEL is installed on the fourth track of the ERL. It includes three undulator sections and 40-meters-long optical cavity. The design tuning range of this FEL is from 5 to 20 microns and the design average power at bunch repetition rate 3.74 MHz is about 1 kW. Recent results of the third stage FEL commissioning are reported.

The high-power free electron laser (FEL) facility NovoFEL has been created at Budker INP. Its wavelength can be tuned over a wide range in terahertz and infrared spectrum regions. This FEL uses a multi-turn energy recovery linac with five straight sections as a source of electron beam. Three sections are used for three FELs which operate in different wavelength ranges (the first at 90-240 μm; the second at 37 – 80 μm; the third at 5 – 20 μm). The first and second FELs were commissioned in 2003 and 2009, respectively. They operate for users now. The third FEL is installed on the fourth accelerator track, which is the last one; the electron energy is maximal here. This FEL comprises three undulator sections and a 40-m optical cavity. The first lasing of this FEL was obtained in the summer of 2015. The radiation wavelength was 9 μm and the average power was about 100 W. Radiation of the third FEL was delivered to the user stations, and the first user shifts were performed recently. The results of the commissioning of the third FEL, the current status of the first and second FELs and future development prospects are presented.

The Novosibirsk Free Electron Laser (NovoFEL) is based on a four-turn microtron-recuperator. To ensure its stable operation and radiation generation, it is necessary to provide a stable mode of electron beam recirculation and minimize beam losses on the vacuum chamber wall on all the beam way in the accelerator beamline. To this end it is necessary to know the longitudinal distribution of these losses along the beamline. A system for registration of beam losses was created. The system applies optical fibers placed along the vacuum chamber and nearby it. If local electron beam losses occur somewhere in the vacuum chamber, electrons falling to the vacuum chamber wall cause generation of X- and gamma rays. This radiation in turn originates optical emission in an optical fiber nearby the region of electron “precipitation” on the chamber wall. Then, executing some transformation and processing of the time dependencies of signals from these optical fibers, one can obtain the longitudinal distribution of electron beam losses along the accelerator line in all its four turns.

The Novosibirsk free electron laser is the first multi-turn energy-recovery linear accelerator with three separate laser systems (the terahertz, far-infrared and mid-infrared ones). The facility is well equipped with optical elements and instrumentation available to Russian and foreign users. In this paper, we describe in brief the workstations of the facility and survey selected recent experiments using intense monochromatic terahertz laser radiation, which can be tuned from 90 to 240 μm.

The Novosibirsk Free Electron Laser (NovoFEL) facility is able to produce high-power tunable terahertz (THz) laser radiation in quasi-continuous mode. The ability to control/shape this THz radiation is required in a number of user experiments. In this work we propose a modulation approach suitable for free electron lasers based on recuperation design. It allows for generating THz macropulses of a desirable length, down to several microseconds (limited by a quality factor of FEL optical resonator). Using this approach, macropulses in the time window from several microseconds to several hundred microseconds have been shown for three possible frequency ranges: mid-infrared (~1100 cm−1), far-infrared (~200 cm−1) and THz (~40 cm−1). In each case, the observed rise and decay of the macropulse have been measured and interpreted. The advantage of using short macropulses at the maximum peak power available has been demonstrated with the time-resolved Electron Paramagnetic Resonance (EPR) spectroscopy.

Novosibirsk free electron laser (FEL) facility contains three FELs operating in the wavelength range 8–240 micron at average power up to 0.5 kW and peak power about 1 MW. Radiation users works at 6 user stations performing biological, chemical, physical and medical research.

The first stage of Novosibirsk high-power free electron laser (FEL) was commissioned in 2003. It is based on the normal conducting CW energy recovery linac (ERL). Now the FEL provides electromagnetic radiation in the wavelength range 120–230 μm. The maximum average power is 400 W. The minimum measured linewidth is 0.3%, which is close to the Fourier-transform limit. Four user stations are in operation now. Manufacturing of the second stage of the FEL (based on the four-turn ERL) is in progress.

The first lasing near wavelength 140 μm was achieved in April 2003 on a high-power free electron laser (FEL) constructed at the Siberian Center for Photochemical Research. In this paper, we briefly describe the design of FEL driven by an accelerator–recuperator. Characteristics of the electron beam and terahertz laser radiation, obtained at the first experiments, are also presented in the paper.

Longitudinal bunching properties of a classical microtron have been investigated by the numerical simulation of the longitudinal motion of accelerated electrons. The simulations were performed for the 12-turn microtron that has been used as an injector for the KAERI far infrared free electron laser. Based on the bunching properties of the electron beam, the temporal distribution of the coherent undulator radiation power during a macro pulse from the free electron laser was calculated. In the calculations, we took into account the dispersion properties of the accelerating cavity and deviations of the bunch repetition rate that were measured by the heterodyne method in real operating conditions of the microtron. The calculation results are compared with the experimental data.

Different mode regimes vs. extent of stabilization of modulation instability were investigated with a complex diagnostics system. Slippage due to detuning of the frequencies of electron and light pulses turned out to be the main stabilization factor. Spectral and time parameters of the laser, especially radiation of high harmonics, have been shown to strongly depend on the stabilization.

Different mode regimes versus the extent modulation instability stabilization were investigated with a complex diagnostics system. Slippage due to frequency detuning of electron and light pulses turned out to be the main stabilization factor. Spectral and time parameters of the laser, especially the radiation of high harmonics, have been shown to strongly depend on the stabilization.

High power THz applications on the Novosibirsk terahertz free electron laser are described.

Progress in the construction of the second stage of Novosibirsk free electron laser and main results obtained during the year at the terahertz user stations are described.

We have investigated various spectral parameters of Novosibirsk terahertz free electron laser (FEL) in different regimes by Bruker vacuum Fourier spectrometer IFS-66v. In addition to routine wavelength measurement and calibration we studied also radiation of harmonics [1] and detailed form of FEL spectrums. Such interesting phenomena as sideband instability [2] and two wavelength generation have been demonstrated very distinctly in our FEL.

During the past year, generation characteristics of the Novisibirsk terahertz free electron laser were growing up. It generates now coherent radiation tunable in the range 120-170 /spl mu/m at the repetition rate of 2.8-11.2 MHz. Maximum average output power reaches 400 W at 11.2 MHz. Laser radiations are transmitted through a 14-m optical beamline to the user stations. Experiments on chemistry, biology, spectroscopy, imaging and holography with employment of terahertz radiation are in progress.

The first quasi-continuous optical discharge in near sub-millimeter spectral range was demonstrated on high-power Novosibirsk free electron laser. Experimental results and elementary theory of this phenomenon are presented.

Fast Schottky-diode detectors is used for measurement and optimization of main parameters of Novosibirsk free electron laser (FEL) such as losses in optical resonator, small signal gain, optimal output coupling. Possibility of applying of the device for measurement of coherence time and FEL pulse duration is considered. We plan also to calibrate free electron laser wavelengths by this detector and etalon universal gas laser. High sensitivity of the detector allows apply of it in various user's experiments too.

The first stage of Novosibirsk high-power free-electron laser (FEL) was commissioned in 2003. It is based on a normal conducting CW energy recovery linac. Now the FEL provides electromagnetic radiation in the wavelength range of 120…180 micrometers. An average power is 400 W. The minimum measured line width is 0.3%, which is close to the Fourier-transform limit. A user-beamline assembly is in progress, parts of the full-scale machine are manufactured. The latter will operate in the near IR region and provide higher average power В 2003 году в Новосибирске заработала первая очередь мощного лазера на свободных электронах (ЛСЭ). Машина построена на базе линака-рекуператора непрерывного действия. В настоящее время ЛСЭ работает в диапазоне длин волн 120…180 мкм, его средняя мощность достигает 400 Вт. Минимальная измеренная ши- рина полосы излучения составляет 0.3%, что близко к теоретическому минимуму. В настоящее время монтируются каналы разводки излучения для пользователей, части полномасштабной машины запущены в производство. Полномасштабная машина будет работать в ближнем ИК-диапазоне и обладать большей мощностью. В 2003 році в Новосибірську заробила перша черга потужного лазера на вільних електронах (ЛВЕ). Машина побудована на базі лінака-рекуператора безперервної дії. Зараз ЛВЕ працює в діапазоні довжин хвиль 120...180 мкм, його середня потужність досягає 400 Вт. Мінімальна виміряна ширина смуги випромінювання становить 0.3%, що близько до теоретичного мінімуму. Зараз монтуються канали розведення випромінювання для користувачів, частини повномасштабної машини запущені у виробництво. Повномасштабна машина буде працювати в ближньому ІЧ-діапазоні і мати більшу потужність.

Mesh Fabry-Perot interferometers are simplest and most adequate devices for laser spectral measurements in range 20-500 microns approximately. Main design principles of the optimal interferometers are described. Experimental instrumental functions of the devices and investigation of spectral parameters of universal gas laser, Novosibirsk powerful free electron laser and compact KAERI free electron laser are presented.

The first stage of Novosibirsk high power free electron laser (FEL) was commissioned in 2003. It is based on normal conducting CW energy recovery linac. Now the FEL provides electromagnetic radiation in the wavelength range 120-180 micron. The average power is 100 W. The measured linewidth is 0.3%, which is close to the Fourier-transform limit. The assembly of user beamline is in progress. Plans of future developments are discussed.

The Novosibirsk FEL (NovoFEL) generates tunable monochromatic coherent radiation as a continuous stream of 100-ps pulses with a repetition rate of up to 11.2 MHz and average power of up to 500 W. After commissioning of the second laser resonator in 2010, the spectral ranges of 120–240 μm and 40–80 μm are available to users. A review of experimental results for the past year is given.

Two types of powermeters for the Novosibirsk terahertz free electron laser (NovoFEL) are considered in this paper. The first one is an expositional etalon device on the basis of a heat isolated sapphire plate. The calorimeter is shown to have a constant emissivity of 0.74 in the entire generation range of NovoFEL. The second device is a CW calorimeter with a special absorption cone with an Al2O3 ceramic coating made by a gas dynamic method. Two 2D beam imaging systems with 152 mm times 152 mm workspace are presented. The first one is a thermofluorescent screen with an optical video camera, and the second one is a scanning ID line of thirty piroelectric detectors. Small beams and objects will be investigated by a commercial Pirocam III piroelectric camera with 12 mm times 12 mm workspace.

Radiation of the Novosibirsk terahertz free electron laser (NovoFEL) is transported to user stations by a 40 m long optical channel. A high vacuum volume of the NovoFEL and the optical channel are separated by a CVD-diamond window. Because of a sufficiently large size of submillimeter beams and the absence of chip and firm vacuum windows of an adequate size, we use a nitrogen-filled channel at normal atmospheric pressure and thin polypropylene windows for radiation coupling on the user stations. The main problem of the long channel is water vapor absorption. A special system of drying with round circulation was made on the basis of a zeolite absorber. A combination of Fourier and free electron laser spectroscopy of the system is presented in this paper.