IR wavelength-selective laser desorption via O–H and C–H stretching modes

We present new results on wavelength-selective desorption of solid samples using the resonant interaction between the laser beam and the bulk. The experimental set-up is based on the coupling of three techniques: laser desorption in the near-infrared (IR) (2.7–4 mm) with a tunable IR optical parametric oscillator (OPO), UV multi-photon ionization, and reflectron time-of-flight mass spectrometry. The resonant character of the laser desorption process has been investigated for an ice/polycyclic aromatic hydrocarbon (PAH) mixture, by excitation of the O–H and C–H stretching modes. Highly preferential desorption has been evidenced, with exclusive desorption of water and PAH molecules at the O–H and C–H resonances, respectively. Potential analytical (e.g. selective analysis of complex samples) and technological (e.g. dry laser cleaning, DLC) applications are discussed.