Modified trim cut method with low level of invasion into the process is developed for visualization of laser cutting process. The method consists in high speed filming via transparent plate which slides with respect to the metal to allow visual access and simultaneously serves as the second missing wall of the kerf. The method is suitable for visualization in conditions equivalent to industrial cutting process in a wide range of plate thicknesses. High speed recordings are done for cutting of mild steel with oxygen and stainless steel with nitrogen. The effect of radiation wave length on the surface quality is studied by comparison of CO2 and fiber laser processing. The obtained results suggest that in case of oxygen assisted cutting, the combustion effects dominate on the surface quality and the effect of the radiation wavelength is moderate. In contrast, inert-gas-assisted cutting visualization reveals very high sensitivity to hydrodynamics of the melt flow which is strongly dependent on the radiation wavelength.