Laser–ion coaxial beams spectrometer

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Abstract
An apparatus has been constructed to provide laser excitation of ion beams in both coaxial and crossed configurations. The coaxial geometry provides very high sensitivity and nearly Doppler-free wavelength resolution for spectroscopic measurements, and allows the use of the Doppler shift to ’’tune’’ the wavelength. A novel transverse quadrupole electric field arrangement is used to deflect the ion beam into and out of the laser beam axis. The ion beam is highly collimated and a high-resolution 180° electrostatic analyzer is used for photofragment energy analysis. The apparatus has demonstrated a resolution of better than 10 meV for normal photofragment spectroscopy and 0.001 meV for coaxial beams photofragment spectroscopy using a single-mode laser. While providing these high resolutions the apparatus has an overall sensitivity several orders of magnitude greater than conventional ones.