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Doped AunX+ clustersNd:YAG
The vaporization lasers used for cluster production are two Q-switched Nd:YAG lasers (Quanta Ray Indi-series, Spectra Physics) equipped with an Harmonic Generator option. After pumping with a flash lamp, whose output matches principle absorption bands in the red and near infrared, the most probable lasing transition emits a photon at 1064 nm. Because the upper level of the transition has a long lifetime, a large population of excited neodymium ions can build up in the YAG rod. Therefore the lasers are equipped with an electro-optic device (Q-switch), which prevents oscillation while the population inversion builds up, and subsequently quickly releases the stored energy, resulting in a short pulse of high intensity laser light. The 1064 nm Nd:YAG fundamental wavelength interacts with a nonlinear crystal to produce a secondary wave with half the fundamental wavelength.
After frequency doubling the resulting 532 nm wavelength has pulse energies of about 240 mJ. The pulse width is 5-8 ns and the lasers operate at a repetition frequency of 10 Hz. The beam diameter is about 7 mm, which is focussed to about 1 mm onto the target sample surface. The second harmonic 532 nm wavelength is used for laser vaporization of all target material samples. It is preferred over the infrared 1064 nm beam for efficiency, alignment and for safety reasons.
Pieterjan Claes