Two-photon excitation of the CaI radical

Fluorescence in the UV (315-330 nm) following visible (620-655 nm) laser excitation of the B and A states of the CaI radical has been detected. The UV excitation spectrum consists of sharp peaks in coincidence with narrow regions of the DELTAv = 1,0 sequences of the B2SIGMA+-X2SIGMA+ and A2PI1/2-X2SIGMA+ visible systems. The main peaks are tentatively assigned to resonance-enhanced excitation of a single vibrational level of the D2SIGMA+ state from successive vibrational levels of the ground state. The excitation process is a one-color two-photon optical-optical-double-resonance via B2SIGMA+ and A2PI1/2 intermediate levels.