The invention relates to a method and system for ionizing analyte-containing sample lying on a surface of a substrate. The method comprises directing to the sample a heated flow of desorption gas in order to desorb analyte from the surface, and simultaneously directing to the sample light capable of ionizing the desorbed analyte in the presence of the desorption gas. The invention provides a method and system suitable for efficiently producing ions of neutral and nonpolar molecules on surfaces, for example for mass spectrometric purposes.