**1. Introduction**

Laser systems on the noble-gas halides are the most powerful and effective sources of the coherent radiation in the UV spectral range. Nowadays, these systems serve as a unique means for solving fundamental and applied problems (e.g., inertial nuclear fusion, the physics of the interaction of the superintense radiation with matter, the generation of the x-ray radiation, the acceleration of particles in the presence of superstrong electromagnetic field, etc.).

Nike (United States) is the most powerful excimer laser system, generating radiation pulses with energy of up to 5 kJ at a pulse duration of 240 ns on full width half maximum (FWHM) and a wavelength of 248 nm [1]. The aperture of the output amplifier of this system is 60 × 60 cm. The system was created and applied to solve the problem of laser thermonuclear fusion. It is used in the experiments on the generation of high-power nanosecond pulses and their interaction with a target. The second largest excimer laser system (Super-Ashura) was created in Japan [2]. The aperture size of the output amplifier is 61 cm. This system generates radiation pulses with an energy

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of up to 3.7 kJ (KrF molecule) at a pulse duration of about 240 ns. The Super-Ashura system is used for experiments on the generation of high-power nanosecond and picosecond pulses and the interaction of these pulses with matter. The Titania laser system, created in England, employs KrF molecules and generates pulses with an energy of about 1 kJ and a pulse duration of about 150 ns [3]. The aperture size of the output amplifier is 42 cm. This system is used for experiments on the generation of high-power picosecond and femtosecond pulses and their interaction with matter.

simpler and more efficient methods. The compression of negatively chirped pulses can be realized in bulk glass with positive group velocity dispersion. In addition, the hybrid laser system operates in the visible spectral range, which may be advantageous in some applications to strong-field laser-matter interaction [28]. The gaseous nature of the active medium also allows easy scaling of hybrid laser systems. At the Institute of High Current Electronics (HCEI) SB RAS, the multiterawatt hybrid laser system THL-100 based on a photochemical-

High-Power Laser Systems of UV and Visible Spectral Ranges

http://dx.doi.org/10.5772/intechopen.71455

3

In this work, we describe three high-power excimer laser systems developed at HCEI and based on wide-aperture lasers with the output laser beam sizes 25 × 25 cm [6], 40 cm (diameter) [8], and 25 cm [29, 30], respectively. The experimental results obtained on these systems are presented.

The MELS-4 k laser system consists of the master complex, preamplifier, and a UFL-100 M amplifier [7]. The master complex contains two electric-discharge XeCl lasers. One of them serves as the master oscillator. The combination of the two lasers makes it possible to vary the parameters of the output radiation. In particular, for single-pass lasing, the radiation energy is *E* = 15 mJ, the spectral line half width is Δν = 0.01 cm−1, and the pulse FWHM is 50 ns. In the case of injection locking, the parameters of the output beam are E = 100 mJ, Δν = 0.01 cm−1, and τ = 100 ns, while more than 50% of the radiation energy is concentrated inside the diffraction angle [31]. In the case of double-pass lasing with the phase conjugation, the parameters are *E* = 50 mJ, Δν = 0.01–0.4 cm−1, and τ = 30 ns, and the divergence is close to the diffractionlimited Qd [32]. When the pulse is compressed to a pulse duration of 1–2 ns upon stimulated

The preamplifier represents an electric-discharge lase with an active volume of 6x11x80 cm<sup>3</sup> (**Figure 1**). This laser consists of a metal housing that contains the dielectric laser chamber, capacitors with a total capacitance of 368 nF that are directly connected to the electrodes, and the x-ray source. A discharge gap and a storage capacitor (0.4 μF) are placed outside. The laser mixture Ne/Xe/HCl = 1000/10/1 is photo-ionized at a pressure of 2–4 atm. The storage capacitor is connected to the discharge gap, and 300 ns prior to the moment when the voltage across the electrodes reaches the maximum value, the x-ray source is switched on. The radiation of this source initiates the discharge. The x-ray radiation is injected through a stainless steel grid with a geometrical transparency of 50%. The doze inside the laser chamber is about

beams [6]. The electron accelerators are placed at the top and bottom of the laser chamber, which has an internal volume of 360 l. In each accelerator, the vacuum diode and the high-voltage generator are placed in a single metal housing. The cathode of the vacuum diode is directly fixed on the last stage of the high-voltage generator. The maximum energy of the laser with a plane-parallel cavity is 210 J, and the pulse duration is τ = 250 ns. In the amplification mode, the

. The gas is excited by two electron

relatively to the optical axis.

driven XeF(C-A) boosting amplifier with a 24 cm aperture was developed.

Brillouin scattering, the parameters are *E* = 10 mJ, Δν = 0.01 cm−1, and Qd [33].

25 mR. The laser energy amounts to 6–10 J at a pulse duration of τ = 80–160 ns.

The active volume of the main amplifier is 25 × 25 × 100 cm<sup>3</sup>

windows of the laser chamber are tilted at an angle of 100

**2. MELS-4 k laser system**

**2.1. Experimental method and equipment**

Russian institutions also develop and create the powerful excimer lasers and laser systems [4–12]. In particular, a KrF laser system with a Garpun output unit (Institute of Physics, Russian Academy of Sciences) has an output aperture with a size of 16 × 18 cm and one generates radiation pulses with energy of 80 J and pulse duration of 100 ns [12].

The excimer lasers developed at the High-Current Electronics Institute (HCEI), Siberian Division, Russian Academy of Sciences, generate pulses with an energy of greater than 100 J [4–6, 8–11]. The two most powerful XeCl lasers (308 nm) with apertures of 40 [8] and 60 cm [9–11] generate pulses with energies of 660 J and 1.9 kJ and pulse durations of about 350 and 250 ns, respectively.

At the end of the nineteenth century, the hybrid approach to femtosecond pulse amplification was developed. To amplify femtosecond pulses, the rare-gas-halide excimer media excited by a high-voltage discharge or an electron beam were used. In these media, the laser transitions between the excited B–state and ground weakly bound or weakly repulsive X-state of ArF, XeCl, XeF, or KrF excimer molecules were used [13]. However, B-X transitions have rather narrow gain bandwidths (broadest bandwidth of Δλ ≈ 2 nm) and rather small saturation fluence (*εsat* ≈ 1 mJ/cm<sup>2</sup> ). To realize high-output peak powers, (more than 1 TW) large apertures are required. Furthermore, a high gain of the amplifiers limits the temporal contrast of output radiation at the level of 10<sup>2</sup> –103 [14]. The highest peak power of output radiation reached in traditional rare-gas-halide excimer amplifiers does not exceed ~ 4 TW [15].

А photodissociative-driven XeF(С-А) medium has a wide amplification band (~ 60 nm) in 475 nm range and a high saturation fluence of ~ 0.05 J/cm<sup>2</sup> unlike the traditional excimer molecules on the B-X transition [16]. At present, the development of ultra–high-power laser systems with a pulse duration of 10–100 fs is based mainly on near-infrared solid-state Ti:sapphire or parametric amplifiers. In these systems, positively chirped pulses, i.e., stretched in time (up to 0.5–1 ns) by linear frequency modulation [17], are amplified, and following its temporal recompression, the initial duration is realized. A pulse stretching allows avoiding nonlinear effects related to self-focusing. The pulses are normally stretched ~10<sup>4</sup> times, and for pulse recompression, a vacuum compressor based on diffraction gold-coated gratings is used.

An alternative approach to the design of multiterawatt and petawatt femtosecond laser systems has been developed at the Lebedev Physical Institute (Moscow, Russia) [18, 19], LP3 Laboratory of the Marseille University (Marseille, France) [20–22], and Institute of High Current Electronics (Tomsk, Russia) [23–25]. This approach is based on a solid-state femtosecond front-end and a photochemical XeF(C-A) boosting amplifier with a gaseous active medium [26, 27]. The advantage of this hybrid (solid/gas) design is that due to the much lower optical nonlinearity of gas compared to solids, the admissible factor of stretching femtosecond pulse is three orders of magnitude smaller than for solid-state systems. This allows the amplification of picosecond chirped pulses and their subsequent compression by simpler and more efficient methods. The compression of negatively chirped pulses can be realized in bulk glass with positive group velocity dispersion. In addition, the hybrid laser system operates in the visible spectral range, which may be advantageous in some applications to strong-field laser-matter interaction [28]. The gaseous nature of the active medium also allows easy scaling of hybrid laser systems. At the Institute of High Current Electronics (HCEI) SB RAS, the multiterawatt hybrid laser system THL-100 based on a photochemicaldriven XeF(C-A) boosting amplifier with a 24 cm aperture was developed.

In this work, we describe three high-power excimer laser systems developed at HCEI and based on wide-aperture lasers with the output laser beam sizes 25 × 25 cm [6], 40 cm (diameter) [8], and 25 cm [29, 30], respectively. The experimental results obtained on these systems are presented.
