It is well established that color centers (CCs) produced by ionizing radiation or short-wave radiation of the pump lamp, strongly influence the optical characteristics of yttrium-aluminium garnet (YAG) single crystals. Many publica tions, including reviews and monographs [1-3], are devoted to this problem. Tle most thoroughly investigated aspect was the influence of various types of ionizing radiation (gamma quanta, electrons, neutrons) on performance of YAG crystals activated with Nd ions [2]. The CCs, arising in the crystals, absorb not only pump light but also laser light, significantly increasing laser energy losses [4]. Creating losses at the laser wavelength [5], the CCs reduce the slope of efficiency. In Ref. [6] the improvement of performance of Nd:YAG lasers was reported as an effect of small dose of gamma and electron irradiation. During optical investigations of Nd:YAG crystals, particular attention was paid to Cr3+ ions, because they not only sensibilize the laser medium but, at certain concentrations, they may also reduce the susceptibility of YAG crystals to ionizing radiation effects [7].