Silicon Isotope Enrichment by two-frequency IRMPD

MATÍAS ARIEL RISARO; LAURA AZCÁRATE; JORGE CODNIA; VIOLETA D'ACCURSO

Pucón

Conferencia; RIAO OPTILAS 20116; 2016

InfraRed Multi-Photon Dissociation (IRMPD) is a highly selective laser isotope separation technique. This process consists of a sequential IR photon absorption from the ground vibrational state up to dissociation by a molecule that contains the isotope of interest. In order to overcome the dissociation threshold, large intensity radiation fields are needed. This leads to a power broadening of the vibrational energy levels that reduces the dissociation selectivity. Moreover, the overall IRMPD yield decreases with molecular excitation since, due to anharmonicity, the radiation field is no longer resonant. The use of two IR laser frequencies can avoid these undesired effects: a low energy laser resonant with the first energy levels will guarantee isotope selectivity excitation while, a second non-resonant large energy laser would allow achieving molecular dissociation. In this work, two home-built TEA CO2 single transverse mode lasers were used as the excitation and dissociation sources. Both IR laser beams were combined in a ZnSe beam splitter and entered the vacuum chamber through a CaF2 window in a collinear configuration. A Time-of-Flight mass spectrometer with UV multi-photon ionization was used to monitor the dissociation process. The sample injection, excitation, dissociation and ionization pulses' timing was controlled by a pulse delay generator. The time delay between the sample inlet and the dissociation and ionization lasers was varied so as to optimize the signal intensity. We characterized the two-frequency IRMPD by analyzing the isotope dissociation estimator, α, and the isotope enrichment factor estimator, β. In order to optimize the isotope enrichment process, we analyzed the laser excitation fluence and wavelength dependence of α and β.