It may mean that the gain of the laser medium should be doubled, for example, doubling the population of the upper laser level in a quasi-two level system (assuming negligible absorption of the ground-state).
ɪt mˈeɪ mˈiːn ðætðə ɡˈeɪn ʌvðə lˈeɪzɚ mˈiːdiəm ʃˌʊd biː dˈʌbəld, fɔːɹ ɛɡzˈæmpəl, dˈʌblɪŋ ðə pˌɑːpjʊlˈeɪʃən ʌvðɪ ˌʌpɚ lˈeɪzɚ lˈɛvəl ɪn ɐ kwˈeɪzaɪtˈuː lˈɛvəl sˈɪstəm ɐsˈuːmɪŋ nˈɛɡlɪdʒəbəl ɐbsˈoːɹpʃən ʌvðə ɡɹˈaʊndstˈeɪt.