Laser Spectroscopy

Laser Spectroscopy

Schematic experimental setup.
Schematic experimental setup.

When a gas phase cluster interacts with light various processes can occur. A possible one photon process is the fragmentation of a neutral cluster, if the sum of the absorbed photon energy and the internal energy of the cluster is above the dissociation threshold. Due to the small cluster concentration in the gas phase it is not possible to perform a “normal” absorption experiment. Therefore, the spectral information is gained by coupling the experiment to mass spectrometric measurements. A typical experiment is performed in a supersonic molecular beam, where all objects travel on the same axis. If a photon induced cluster fragmentation occurs, the produced fragments will most likely leave the predefined molecular beam axis. Consequently, a mass spectrum recorded on the beam axis and behind the laser excitation region will show a depletion of the fragmented cluster. Therefore, measuring the depletion of the mass signal as a function of photon energy enables to record the UV-Vis spectrum of gas clusters. The experiment is realized in a high-vacuum apparatus, equipped with a laser vaporization source, an orthogonal time-of flight spectrometer and flash lamp ionization source. The tuneable laser source (NIR-UV) is an optical parametric oscillator pumped by a third harmonic of a Nd:YAG and the corresponding second harmonic generator unit.