This paper discusses copper-activated aluminopotassium barium phosphate glasses similar in composition to the matrix of KGSS 0180/35 phosphate laser glass, used to fabricate large-scale disk-shaped active elements of powerful laser systems with high output energy. The glasses were melted at various temperatures under neutral or oxidizing conditions. The quantitative Cu+/Cu2+ ratio and the contribution of the Cu2+ ions to the index of inactive absorption of the glass at the lasing wavelength (1.053 µm) was studied as a function of its melting conditions. The studies used absorption, luminescence, mass-spectrometric, and x-ray photoelectron analysis. It is established that the quantitative Cu+/Cu2+ ratio in the test glasses is mainly determined by the melting temperature at the homogenization stage of the glass.