Method for desorbing and ionizing of sample material

A method for desorbing and ionizing of sample material deposited on a sample support 115 comprises repeatedly locally impacting sample material using a first energetic radiation 112 (e.g. a MALDI desorption laser beam) to desorb sample material into the gas phase. The position of the first energetic radiation is varied relative to the sample support to achieve a plurality of impingement or ablation positions. The method further comprises pulsed impacting the locally desorbed sample material using a second energetic radiation 112* (e.g. a post-ionisation laser beam) to trigger ionisation or increasing the degree of ionisation of the locally desorbed sample material. A focus or beam waist position of the second energetic radiation can be moved (e.g. using mirrors or lenses) so that it is positioned substantially opposite to (e.g. matching) a current impingement point of the sample material. This may provide optimal interaction between the energy in the post-ionisation laser beam and particles in the desorbed sample material cloud.