The combination of laser desorption followed by multiphoton ionization (MPI) with time of flight mass spectrometry (TOF/MS) produces a versatile method of high sensitivity and selectivity. The first step is laser desorption in which molecules are desorbed from the sample intact or with little degradation. Laser ionization is employed as the second step to produce the ions and also induce fragmentation. Soft ionization, which yields primarily the parent ion, and hard ionization, which yields primarily the fragments, are both possible.

Instrumental details are described and preliminary results from recent laser desorption MPI-TOF/MS experiments on a perbenzoylated sugar and on a porphyrin are presented. Examples from single photon ionization (SPI) experiments on two alkanes are also shown.
J. Anal. Appl. Pyrolysis

Weeding, T. L, Steenvoorden, R. J. J. M, Kistemaker, P. G, & Boon, J. J. (1991). Laser desorption multiphoton ionization mass spectrometry. J. Anal. Appl. Pyrolysis, 20, 47–56. doi:10.1016/0165-2370(91)80061-C