Laser vaporization source schematic

Figure 1 is a schematic of the laser vaporization source. This diagram depicts a pulsed valve on the left which supplies high pressure helium flow directly towards the right. Several workers have also chosen to use continuous helium f ows(2,6,9). In general these sources are modifications of conventional supersonic beam sources. 

Figure. 1. Schematic of essential components of the Exxon group cluster laser vaporization source and fast flow tube chemical reactor. On the far left is a 1 mm diameter pulsed nozzle that emits an -200 ysec long pulse of helium which achieves an average pressure of approximately one atmosphere above the sample rod. Immediately before the sample rod position the tube is expanded to 2 mm diameter. The length of this extender section can be varied form 6 mm to 50 mm depending upon the desired integration time for cluster growth. The reactor flow tube is 10 mm in diameter and typically 50 mm long. The reactants diluted in helium are added and mixed with the flow stream via the second pulsed valve.

Figure 1 is a schematic of a typical laser vaporization source used in our laboratory. A pulsed valve introduces high-pressure helium over the target, synchronized with the firing of a pulsed laser used to produce the metal vapor. For experiments such as the measurement of absolute reaction rate constants, it is advantageous to use a continuous-flow supersonic beam. ... 

Figure 1. Schematic of laser vaporization source/fast-flow reactor configuration currently employed in our laboratory.

Fig. 1.29. Schematic sketch of the collision cell method for the study of metal cluster reactivity. The supersonic laser vaporization source is depicted on the right hand side. The clusters subsequently pass two collision cells in which reactions can take place. Finally, laser ionization mass spectrometry serves to detect the neutral reaction products [3]...

FIG. 5. Schematic overview of the set-up with the laser vaporization source and the nozzle for supersonic expansion used in the production of clusters at Goteborg. The figure shows the laser vaporization source with the target material, the laser beam for evaporation, the small volume where a plasma of atoms and ions exist and the region where the clusters are formed in the expansion through the nozzle. 

Figure Cl. 1.1. Schematic of a typical laser vaporization supersonic metal cluster source using a pulsed laser and a pulsed helium carrier gas.

Figure 1. Schematic illustration of the laser-vaporization supersonic cluster source. Just before the peak of an intense He pulse from the nozzle (at left), a weakly focused laser pulse strikes from the rotating metal rod. The hot metal vapor sputtered from the surface is swept down the condensation channel in dense He, where cluster formation occurs through nucleation. The gas pulse expands into vacuum, with a skinned portion to serve as a collimated cluster bean. The deflection magnet is used to measure magnetic properties, while the final chaiber at right is for measurement of the cluster distribution by laser photoionization time-of-flight mass spectroscopy.

Fig. 1.19. Scheme of the experimental setup for infrared multiphoton ionization or dissociation of clusters or of metal clusters-rare gas complexes. The charged and neutral clusters are directly emitted from the laser vaporization/supersonic expansion source. The beam passes a skimmer and is subsequently crossed by the tightly focused beam of the FELIX. At some time after the FELIX pulse is over, the time-of-flight mass spectrometer acceleration plates are pulsed to high voltage, and a mass spectrum is recorded in a standard reflectron setup. Also schematically depicted is the particular pulse structure of the FELIX light [126,127]... 

Figure 21.1. Photoionization time-of-flight mass spectrum of neutral silicon clusters. The clusters have been ionized with an excimer laser hv = 7.89 eV). In the inset a schematic drawing of the pulsed laser vaporization cluster source is shown.

A detailed description of the interacting beams apparatus used in the present work can be found elsewhere [12], In short, positive ions are extracted from a plasma-type ion source and accelerated to beam energies that can be varied between 2.5 and 5 keV. Negative ions are produced in the beam by double sequential charge exchange in a cesium vapor. A pair of electrostatic quadrupole deflectors (QD1, QD2) is used to direct the negative ion beam into and out of the path of the laser beams, as shown schematically in Fig. 2. The ion-laser interaction region is defined... 

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