ENERGETICS FOR CARBON CLUSTERS PRODUCED DIRECTLY BY LASER VAPORIZATION OF GRAPHITE - DEPENDENCE ON LASER POWER AND WAVELENGTH

Carbon-cluster positive ions C(n)+ have been produced by laser vaporiz ation of a graphite target by using three wavelengths (1064, 532 and 2 66 nm). When the graphite target was placed between the acceleration e lectrodes of a time-of-flight mass spectrometer and irradiated, the ma ss distribution of C(n)+ immediately after the laser vaporization was recorded as a mass spectrum. C(n)+ with n = 1, 3, 5, 7 and 11 atoms we re produced predominantly, and their distribution was found to be depe ndent on the laser power and its wavelength. When the laser power was not too high, the logarithm of the concentration of carbon-cluster ion s is linearly dependent on the logarithm of the laser power density. T his logarithmic relation is well explained by the mechanism that C(n) with 1 less-than-or-equal-to n less-than-or-equal-to 20 is vaporized directly from the graphite through conversion of the multiphoton energ y into thermal energy. Furthermore, contributions of photoelectronic e xcitation to the formation of carbon clusters become important for 266 nm laser irradiation.