G.A. Torchia

The luminescent quantum efficiency of Cr3+ ions in Cs2NaAlF6 single crystals

Abstract The luminescent quantum efficiency of Cr3+ ions in single fluoride crystal Cs2NaAlF6 was determined by using the simultaneous multiple-wavelength photoacoustic and luminescent experiments method, based on the generation of photoacoustic and luminescence signals after pulsed laser excitation. The luminescent quantum yield for the most important transition between the 4 T 2 → 4 A 2 vibronic levels was found to be 68±3%. This value agrees with that obtained from the ratio of the lifetimes of the corresponding transition at different temperatures.Abstract The luminescent quantum efficiency of Cr3+ ions in single fluoride crystal Cs2NaAlF6 was determined by using the simultaneous multiple-wavelength photoacoustic and luminescent experiments method, based on the generation of photoacoustic and luminescence signals after pulsed laser excitation. The luminescent quantum yield for the most important transition between the 4 T 2 → 4 A 2 vibronic levels was found to be 68±3%. This value agrees with that obtained from the ratio of the lifetimes of the corresponding transition at different temperatures.

Electron-lattice coupling in congruent Co-doped LiNbO3:Cr3+:ZnO crystal

The importance of the role of the ion-lattice coupling in determining the energy levels of Cr3+ ions in congruent LiNbO3 crystals doped with 2.9% of ZnO is demonstrated in this paper. The Racah parameters: B = 533 cm-1, C = 3244 cm-1 and the crystal-field intensity Dq = 1527 cm-1 were determined and the Tanabe-Sugano diagram was constructed. The characteristics of the absorption and the emission spectra of Cr3+ ions in these crystals can be explained in terms of the configurational-coordinate diagram in the harmonic approximation, with good agreement obtained. The Huang-Rhys parameter S = 6.86 and the lattice phonon energy ω = 343 cm-1 are also reported in this work.

Site-selective spectroscopy of Cr3+ in congruent co-doped LiNbO3:Cr3+:ZnO crystals

This work reports the energy levels of chromium ions for different sites in congruent LiNbO3 crystals doped with ZnO. Optical absorption and luminescence (fluorescence and excitation) experimental techniques were used. For crystals with Zn2+ concentration less than 4.7%, optical signals correspond to Cr3+ ions substituting for Li+ ions; for higher Zn2+ concentration, signals show two components coming from different sites for active Cr3+ ions. It is accepted that these two components can be assigned to Cr3+ ions substituting for Li+ ions and Cr3+ ions substituting for Nb+ ions. The energy levels of the former site are reported for the first time in this work; the 4T2 and 4T1 levels lie 13?421?cm-1 and 19?550?cm-1 above the 4A2 ground level, respectively. Analysis of the excitation spectra was the key result for achieving the resolution of the new site.

Features of the gouy phase of nondiffracting beams

It is shown how the linear Gouy phase of an ideal nondiffracting beam of +/-(k - k_z)z form, with k_z being the projection of the wavevector of modulus k of the plane wave spectrum onto the propagation axis z, is built from a rigorous treatment based on the successive approximations to the Helmholtz equation. All of different families of nondiffracting beams with a continuum spectrum, as Bessel beams, Mathieu beams and Parabolic ones, as well as nondiffracting beams with a discrete spectrum, as kaleidoscopic beams, have an identical Gouy phase that fully governs the beam propagation dynamics. Hence, a real beam whose Gouy phase is close to that linear Gouy phase in a given range, will have nondiffracting-like properties on such a range. These results are applied to determine the effective regime in which a physically realizable beam can be treated as a nondiffracting one. As a fruitful example, the Gouy phase analysis is applied to fully establish the regime in which a Helmholtz-Gauss beam propagates with nondiffracting-like properties.

Surface roughness dependence of noncollinear phase matching

Spontaneous noncollinear second harmonic generation in potassium dihydrogen phosphate (KDP) crystals was studied theoretically and experimentally as a function of the scattering centres on the surface of the crystal. A model that explains the main features of the second harmonic generated beam was developed in terms of the surface roughness defined by the size of the dispersing grains. It predicts, for the first time, the intensity distribution of the hollow cones obtained in noncollinear phase matching.