Annealing of hydrogenated amorphous silicon (a-Si:H) films by laser scanning is of interest for (e.g.) defect reduction. For reproducible laser treatment, knowledge about temperature and hydrogen diffusion in the laser spot is required. In this study, the temperature of a-Si:H films on glass substrates during scanning with a 532 nm continuous wave laser (laser light almost fully absorbed within films) was determined by measurement of deuterium-hydrogen inter-diffusion and by calculation assuming a linear relation between laser power and temperature and using the silicon melting point as a reference. The good agreement suggests that both methods for evaluation of the temperature during laser treatment are quite reliable. The temperature depending on laser power and scan speed differs for laser treatment from film and glass sides. For laser scanning from the glass side, the presence of contact metallization reduces the temperature within the amorphous silicon film. The laser treatment related hydrogen diffusion length which is of interest for defect annealing follows directly from deuterium-hydrogen inter-diffusion measurements. The photo-darkening effect is studied in relation to laser power and scan speed and a direct relation between hydrogen diffusion length and photo-darkening effect is found. It is demonstrated that temperature calculation is a convenient method and rather generally valid for similar film substrates and comparable laser treatment conditions as applied in this study. The results show that a controlled annealing of hydrogenated amorphous silicon films and devices at temperatures below silicon crystallization by laser scanning is possible.