2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/10386It is shown that the amplification of a light beam by gravitational waves in scalar-tensor theories of gravity is a first order effect in the wave amplitudes. In general relativity, instead, the effect is only of second order.7 pages, LaTex, no figures, to be published in Astrophysical Letters and CommunicationsAstrophysicstext