Studies of nuclear-pumped lasers at VNIIEF were continued after the 1975 devel­opment of the laser setup LUNA-2 M, developed to perform experiments in the lower hall of the VIR-2 reactor (see Fig. 2.5), which provides convenient conditions to carry out laser experiments: a sufficient spatial volume to irradiate large-scale

(100-200 cm) laser setups and a circular rail track with remote-controlled cars that deliver prepared laser setups to the irradiation zone. The presence of a hemispher­ical cavity makes it possible to irradiate laser setups in the lower hall with a spatially localized beam of intense neutron radiation; at the same time, the equip­ment outside of the beam is in a significantly smaller flux of the reactor radiation.

The LUNA-2 M setup (Fig. 2.11a) is one of the three main laser setups that make up the experimental complex near the VIR-2 M reactor [26, 33]. When this setup was used, VNIIEF performed the bulk of the experiments to study the characteris­tics of NPL active media in the visible and IR range of the spectrum [27, 28], as well as the problem of extracting the radiation from laser channels [51-53].

The experimental complex also includes the LUNA-2P (Fig. 2.11b) and LYaN — 2T setups [26, 28]. The basic characteristics of these setups are given in Table 2.5. Each setup consists of two laser cells (channels) that are identical in design and in irradiating conditions, making it possible to accelerate the rate of the investigations. The layout of the laser setup under the reactor core is shown in Fig. 2.12. The cars can be moved on the track and clamped under the reactor core remotely (from the control panel) or manually (directly in the lower reactor hall).

The LUNA-2P unit (Fig. 2.13) was developed in 1987 and was used to study laser characteristics and the optical quality of the gas medium in the gas flowing mode. The gas was circulated in the transverse direction relative to the optical axis at a speed of 5-10 m/s. Heat exchangers (radiators) were used to cool the gas— packets 100 cm long made of aluminum or beryllium plates 0.5-mm thick, with 0.5­mm gaps between them.

The LYaN-2T setup, developed in 1991 to study lasers operating on metal vapors and to study the influence of temperature on laser parameters, used quartz laser cells 3.2 cm in diameter with electrical heaters filled with a mixture of the isotope 3Не and laser gas. In this case, the active media were excited by the nuclear

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Fig. 2.12 Diagram of laser setup in lower hall of reactor VIR-2 M [28]: (1) reactor core,

(2) neutron moderator, (3) plates with uranium layers, (4) cavity mirrors, (5) beam splitters, (6) focusing lens, (7) laser energy meter, (8) adjustment laser, (9) photoreceiver, (10) light filters, (11) cell gas mixture exhaust and filling system, (12) car, (13) protective shutter, (14 and 15) spectral devices

reaction products 3He(n, p)3H. A detailed description of the LYaN-2T setup is considered in study [54].

The energy parameters of the laser radiation were determined using the laser pulse energy meters IEK-1 and IMO-2 N, various photocells (F-28, FEK-11, FEK-14, and SDF-7) and photoresistors (PbS, PbSe). For measuring the spectra of laser radiation in UV, visible, and near-IR ranges of the spectrum, the spectro­graphs DFS-452 and MS257 were used, and in the mid-IR range, the monochro­mator MDR-2 with a PbSe photoresistor array. The absorption (reflection) spectra of optical materials and cavity mirrors were determined using various spectropho­tometers (IKS-14A, SF-9, etc.).

In the first stages of the investigations, electrical signals were registered using various multibeam oscillographs. At present an automated system is used for recording and processing measurement results using computer technologies.

From 1975 to 2010, around 3,000 pulses were produced on the VIR-2 and VIR-2 M reactors to study the characteristics of gas NPLs. As a result of these investigations, lasing was achieved and studied in the visible and IR ranges of the spectrum at roughly 40 transitions of the atoms Xe, Kr, Ar, Ne, C, O, N, and Cl and the ions Cd+ and Zn+ with excitation of gas mixtures at atmospheric pressure with uranium fission fragments and nuclear reaction products 3He(n, p)3H [1, 7, 27, 28]. In addition, a number of important tasks related to the study of optical and gas-dynamic characteristics of gaseous media were completed, and the information needed to develop CW multichannel NPLs was obtained [15, 16, 37].