S. Behrouzinia Photonics and Quantum Technologies Research School, Nuclear Science and Technology Research Institute, PO Box 14399511-13, Tehran, Iran sbehrouzi@aeoi.org.ir International Journal of Fundamental Physical Sciences (IJFPS) 10 3 27-30 September, 2020 2231-8186 https://doi.org/10.14331/ijfps.2020.330138 The paper presents the experimental results on how the tube bore of copper bromide laser influences the gain radial distribution. A pair of copper bromide lasers in an oscillator-amplifier configuration was operated to measure and compare the small-signal gains of different laser tube bores. It was shown that while the gain radial distribution varies with bore size—similar to temperature profiles—the average radial gains across the tube cross-sections remain the same. Copper bromide laser, Gain radial distribution, Tube bore https://creativecommons.org/licenses/by-nc/4.0/