Fresnel losses occur between two different media that have different refractive indices. To reduce these losses we can change the angle of incidence to brewster's angle. At this angle, the amount of reflective loss is minimized for p-polarized light.
Do we assume that laser light is p-polarised to begin with? Is the flashlamp / flashtube p-polarised? After population inversion and electron's giving off photons, they do so in a p-polarised way?