The results of investigations of the divergence of an amplified diffracted beam of diameter from 1.5 to 150 mm produced by a XeC1 laser are presented. It has been shown that if the intensity distribution of the amplified radiation is spatially nonuniform, the wave front in the active medium changes substantially due to the diffraction of the radiation at a small-diameter diaphragm. The active medium of the amplifier excited by an electron beam makes it possible to amplify without visible distortions a laser beam with a divergence of-10 I.trad.A possible way of producing high-power UV radiation pulses with high spatial coherence is to amplify the beam of a master generator (MG) in one or several excimer amplifiers. It is well known that in this case the smallest achievable divergence, being proportional to the ratio )riD, where ~, is the radiation wavelength and D is the diameter of the diaphragm, is limited by the diffraction of the radiation at the diaphragm. In practice, however, especially for large-diameter laser beams, there always exist some difficulties in the achievement of a nearly diffraction divergence. This is related both to the distortions of the wave front in the optical path and to the influence of the amplified spontaneous radiation flows.This paper presents the results of investigations on the formation of radiation pulses with a divergence close to the diffraction limit inherent in XeC1 amplifiers excited by an electrical discharge or an electron beam. In the experiments trader discussion, some units of the MELS-4k laser system were used [1]. Initially, to achieve a minimum divergence of the laser beam, two diaphragms of diameter 1.4 mm were mounted in the resonator of the master generator. The beam divergence was measured by two methods: from the radiation energy, with the use of calibrated diaphragms, and from the radiation intensity, with the use of a mirror wedge attenuator.The formation of a laser beam, whose divergence is close to the diffraction limit, in a MG is realized due to the use in the resonator of diaphragms with a small coupling hole (1-1.5 mm). Because of the diffraction of the MG beam at the diaphragm, the beam field is highly inhomogeneous in a near zone [2]. The intensity distribution over the beam cross section varies substantially over a length of 3 m: the irregular annular structure gradually changes into a more homogeneous central spot. After the 3-m pass of the beam, the intensity distribution over its cross section practically ceases to vary.Amplification of such a beam of diameter 1.5 mm in the homogeneous medium of an electric-discharge amplifier under the conditions of saturation has shown that the energy divergence of the output radiation depends substantially on the distance between the MG and the amplifier (Fig. 1). In the case where this distance L0 was 1 m, i.e., the intensity distribution over the beam cross section was nonuniform, the directional diagram of the amplified radiation broadened substantially. For the case of L0 = 3 m, where the cross-sectional d...
