Laser Photo-Detachment in Molecular Beams

If the binding energy differs for different isobars of a species, photo-detachment can be used for efficient selection of the wanted isobar. 

The photo-detachment probability might depend on the polarization state of the laser. Detachment with linear polarized lasers can lead to interference effects between electrons ejected into different directions but collected again by the electric extraction field. This effect differs for circular polarization. 

A collinear scheme for ion- and laser beams enlarges the interaction time between the laser and the negative ions. The synchronization of the laser pulses with the pulsed ion source ensures an optimum time overlap between the ion pulses and the laser pulses. The electrons are focussed by a weak magnetic field onto the electron detector. The remaining negative ions are separated from the neutrals by a perpendicular electric field. 

With this technique the photo-detachment spectrum of NO ions has been measured [493]. Here the laser beam is reflected by a gold mirror into the anti-collinear direction of the ion beam (Fig. 4.36). The assembly is located in an electrode arrangement of three electrodes creating an electric field that bumps the ion packet over the mirror and returns it to the incident beam axis. 

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