Observation of retention of optical absorption change in methylene blue sensitized gelatin and polyvinyl alcohol plates on He-Ne laser irradiation

The photochemical reactions of methylene blue in gelatin and polyvinyl alco hol matrices due to He-Ne laser exposure are investigated. Laser irradiatio n results in the formation of a new absorption peak which matches with that of thionine. Retention of this optical absorption change due to irradiatio n for several months is observed. The present study confirms that on irradi ation some irreversible changes are also occurring in methylene blue in add ition to the reversible change to leuco methylene blue. Possibility of perm anent recording is suggested.