Studies of two-photon excitation and vacuum ultraviolet fluorescence in Nd:YLF

Two-photon ultraviolet laser excitation of Nd:YLiF4 was studied via the observation of the vacuum ultraviolet fluorescence from localized states of the 4f25d configuration of the Nd3+ ion. Details of the laser excitation schemes, the fluorescence spectra, and the excitation laser intensity dependence of the fluorescence signals are discussed. A series of experiments demonstrated that the vacuum ultraviolet 4f25d→4f3 fluorescence spectrum following two-photon excitation is independent of the excitation laser wavelength. Our studies also revealed significant fluorescence reabsorption effects. Comparisons are made with earlier single-photon excitation studies in this system.