An approach to bolometry has been developed. It is based on the measurements of optical reflectivity change of a thin metal layer deposited on a transparent substrate. The reflectivity change results from the temperature rise due to absorption of energetic particles or x rays. The sensor of the bolometer has no ohmic contact with the measuring unit, making this method well suited for an environment with strong electromagnetic noise interference. The technique was applied to characterize a method for the generation of intense electron beams in a dense gas. Very high efficiency for the e-beam generation (up to 95%) was measured.