Infrared femtosecond laser preionization in secondary ion mass spectrometry of silver surface.

An alternative secondary ion mass spectrometry utilizing laser preionization is introduced. The native Ag sample surface is first irradiated with laser pulse (100 fs duration, 10(10)-10(11) W/cm(2) intensity, 1240 nm wavelength) and subsequently bombarded with primary ions (Bi(3)(+), 10 ns duration, 25 keV energy). Multiple correlation patterns are observed in the mass spectra, confirming the mutual laser-secondary ion mass spectrometry (SIMS) interplay in the preionization mechanism. The Ag(+), C(3)H(5)(+), C(3)H(5)O(3)(+), and AgOH(+), C(4)H(5)O(4)(+) are observed with the shallow and steep increasing of intensities at 1.3 × 10(11) W/cm(2) and 1.5 × 10(11) W/cm(2), respectively. Two ionization mechanisms are identified, the ion sputtering regime for intensities of less than 1.4 × 10(11) W/cm(2) and the multiphoton ionization at higher intensities. The Ag saturation intensity obtained from fitting is 2.4 × 10(13) W/cm(2), close to the one reported for postionization. The proposed preionization approach might eliminate the need for high peak power/high intensity laser source and, moreover, the experiment geometry ensures that large areas of the sample are affected by the laser beam.