Laser–ion coaxial beams spectrometer

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.

Photofragment spectroscopy of O3+

“…[12][13][14][15] The 0; ions were produced from Os in a hollow cathode ion source. 12 For most of the work reported here, intracavity photons from a laser were crossed with an ion beam, with the laser polarization parallel to the ion beam direction. Fifteen wavelengths were used, ranging from 4579 to 7525.A, generated by argon ion, krypton ion, and tunable dye lasers.…”

Near-Threshold Photodissociation of ColdCH+in a Storage Ring

“…A number of detailed laboratory experiments [8] have studied CH 1 photodissociation close to threshold. Most data have been contributed by laser-ion-beam photofragment spectroscopy [9], a technique where molecular ions are produced in an ion source, accelerated to a few keV, and photodissociated by a merged laser beam [10]. On account of the high fragment detection efficiency and the small Doppler broadening attainable with fast ion beams, this technique has been widely successful in studies both of molecular structure and of dissociation dynamics.…”

“…Our setup, similar in principle to a laser-ion photofragment spectrometer [10], uses the TSR storage ring [19] (Max-Planck-Institut für Kernphysik, Heidelberg, Germany) to store the molecular ion beam. CH 1 is produced from CH 2 molecules created in a cesium sputter source and stripped in a tandem Van-de-Graaff accelerator.…”

Spectroscopy of molecular ions: Laser induced predissociation of O 2 +

“…This cylindrial capacitor has a nominal radius of 10 cm and slit widths of 1 mm to provide a large transmission. For further studies, in which the initial kinetic energies released in the fragmentation process will be determined, the ion deceleration system [8,18] held at ground potential for the present measurements can be activated to give a high initial kinetic energy resolution. For example, the determination of the energy spread of the parent ions from our ion source gives a value of less than 1 eV.…”