We have developed a laser desorption postionization (LDPI) mass spectrometer in our laboratory for the surface chemical analysis of organic and polymer films. It uses laser pulses to desorb intact neutrals from a surface by thermal or photochemical excitation. These neutrals are then single photon ionized by a second, vacuum ultraviolet laser pulse. Separation of the desorption and ionization steps in both time and space allow two-step laser mass spectrometry to provide unambiguous surface chemical information.

The instrument consists of a sample plate with 349 nm desorption laser operating at up to 1 kHz repetition rate and 5 micron minimum spot size, 157 nm VUV postionization laser, and orthogonal extraction ion optics.  Samples are analyzed in microprobe mode and can be imaged by rastering the x-y stage. The ion source also incorporates digital optical imaging of the sample surface, which allows for correlation of mass spectral and optical images.