Arsenic beam from a MBE source characterized by femtosecond laser spectroscopy

are the constituents of a molecular beam. Of importance are parameters such as laser intensity, pulse duration, and laser wavelength for a quantitative characterization and thereby improvement of MBE sources. This would help to optimize the epitaxial growth process. We demonstrate that nonresonant multiphoton ionization (MPI) by fs laser pulses leads to detection of the parent molecule, whereas nonresonant MPI with ns laser pulses leads to strong fragmentation.