Single-frequency excitation resonance enhancement

Fig. 25. Room temperature Raman spectra for purified single-wall carbon nanotubes excited at five different laser wavelengths, showing evidence for the resonant enhancement effect. As a consequence of the ID density of states, specific nanotubes (n, m) are resonant at each laser frequency [195].

Both the high species selectivity and the soft ionization make resonance enhanced multiphoton excitation an excellent ion source for chemical trace analysis. In addition, the use of pulsed lasers combined with TOF mass spectrometry (also a pulsed technique) enables the recording of single mass spectra within a few milliseconds, depending on the repetition frequency of the laser pulses (typically 20 to 50 FIz). The unification of high speed, selectivity and sensitivity indicate that multiphoton mass spec-... 

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