Two-photon dissociation of BeH⁺ with a middle ultraviolet band laser

Two-photon dissociation of BeH⁺ ions is studied by detecting the fluorescence changes of Be⁺–BeH⁺ bi-component Coulomb crystal in a linear Paul trap. BeH⁺ ions generated by an exothermic reaction between electronically excited Be⁺ ions and residual H₂ in the vacuum chamber are photon-dissociated with two photons scanning over the range of 201 nm to 208 nm. Our experiment provides a novel method to maintain the number of Be⁺ ions stable in a Coulomb crystal with a middle ultraviolet band dissociation laser. This two-photon dissociation method extends the wavelength range of the dissociation laser for BeH⁺ compared to the one-photon dissociation, and the method can be utilized to all alkaline earth atomic ions which require suppression of the reaction with residual H₂ gas in vacuum.