Paul Moretti

Luminescence of Nd3+ in proton or helium-implanted channel waveguides in Nd:YAG crystals

Abstract Positive index changes were induced by ion implantation in neodymium doped YAG, in strip areas written by means of a specific slit-based set up, allowing efficient channel waveguiding. Thick waveguides (10 μm) were in particular formed by using H + ions. Very similar neodymium IR emissions to the one of the bulk were recorded around 1.06 μm, for an excitation at 810 nm, in both kind of waveguides.

Mode analysis in He+-implanted lithium fluoride planar waveguides

The depth refractive index profiles of broadband visible-emitting planar waveguides produced in LiF crystals with 1.5- and 2-MeV He+ ions at different doses have been derived from mode analysis. They show that there are two competitive mechanisms responsible for positive and negative modifications of the refractive index in the irradiated volume associated with different processes of energy deposition of the incident ions, so as to induce a complex coloration profile along the penetration direction, which is strongly dependent on the irradiation dose.

Specific behavior of refractive indices in low-dose He+-implanted LiNbO3 waveguides

Y- or Z- cut LiNbO3 crystals were implanted at room temperature by helium with energy in the MeV range and various doses with a specific care for the 1010–1016ions∕cm2 range. The induced structure defects were investigated by micro-Raman and IR reflectivity. IR Brewster angle technique was applied for detailed measurements on both indices variations in nuclear collision damaged areas. It is established that a transition from point to extended defects occurs at some threshold dose around 1.5×1015ions∕cm2 and that the extraordinary index is increased in a specific dose range around this threshold. A model based on depolarized cluster formation is proposed to explain the difference observed between the changes of ordinary and extraordinary refractive indices.

Praseodymium-doped planar multidielectric microcavities: induced lifetime changes over the emission spectrum

We study lifetime modifications induced by luminescent microcavities in the case of praseodymium-doped planar Ta2O5–SiO2 multidielectric structures. From the experimental point of view we measure different decay times of the 1D2 excited level for different wavelengths in the inhomogeneous praseodymium emission spectrum. Decay times depend on the spectral detuning between considered ions and the cavity, and we observe significant changes around the resonance wavelength of the microcavity. The decay times are explained with an electromagnetic modal analysis of spontaneous emission developed in the case of less-loss microcavities.

Concentration of F2 and F3+ defects in He+ implanted LiF crystals determined by optical transmission and photoluminescence measurements

Abstract Lithium fluoride (LiF) crystals and films treated with ionizing radiation are promising materials to realize light emitting devices in the visible spectral range. We studied the ion dose dependence of the concentration of F 2 and F 3 + active defects, both absorbing at about 450 nm and separately emitting in the visible range, in He + implanted LiF crystals. Quantitative information was deduced from transmission measurements by using a specially developed theoretical model to fit them, and was compared with the results obtained from photoluminescence spectra. Their qualitative agreement confirms the validity of our theoretical approach, which provides a simple and versatile tool of investigation of these peculiar active defects.

Guiding properties and nonlinear wave mixing at 854 nm in a rhodium-doped BaTiO 3 waveguide implanted with He + ions

For the very first time to our knowledge, guided waves at 854 nm are observed in a BaTiO3:Rh waveguide fabricated by the technique of ion-beam implantation. The photorefractive interaction between two guided modes is demonstrated and characterized. The experiments revealed that the gain direction is reversed in the guiding layer in comparison with that in the bulk. A maximum gain of 24 cm-1 is achieved.

Leakage of a guided mode caused by static and light-induced inhomogeneities in channel HTPE-LiNbO 3 waveguides

In this paper, we report characterization of insertion losses, mode profiles and intensity distributions in channel LiNbO3 optical waveguide fabricated by High-Temperature Proton Exchange (HTPE). Optimal fabrication parameters were chosen in accordance with results obtained for test samples of a planar waveguide. A target wavelength of our optimization procedure was 810 - 840 nm, as fabrication of phase modulator used in sensor is developed. The guided mode intensity has been mapped by scanning near-field optical microscopy with a sub-wavelength resolution (<100 nm), simultaneously with observation of the topography of the scanned area (100 μm x 100 μm). These measurements offer important information about loss mechanisms in our waveguides.

Color center luminescence decay times in optical microcavities based on LiF films

Abstract Controlling and modifying spontaneous emission in optical microcavities is of great interest for both their basic properties and for their potential applications in emitting solid-state devices. Spatial and temporal spontaneous emission modifications of F 2 color centers in LiF films placed inside planar optical microcavities are reported. Angularly resolved photoluminescence measurements show a narrowing and an enhancement of the emission spectrum along the cavity axis; time resolved luminescence measurements in different geometrical configurations show a shortening of luminescence decay time along the microcavity axis.

H+ implanted channel waveguides in buried epitaxial crystalline YAG:Nd,Tm layers and infrared-to-blue upconversion characterization

Nd,Tm:YAG codoped single crystal waveguides were studied in order to discover if the presence of Nd3+ ions favors blue luminescence at 486 nm. Innovative implantation techniques were applied to locally change Δn and form varied H+ implanted channel structures in Nd,Tm:YAG buried epitaxial waveguiding layers. The guided blue luminescence due to the Tm3+ G14→H36 transition was studied under infrared excitation at 785 nm (Tm3+ absorption) and 808 nm (Nd3+ absorption) for the epitaxial planar waveguides of different Tm3+ and Nd3+ concentrations for all the implanted channel waveguide structures.

Mechanical properties of dielectric thin films

Stress in thin films deposited by Reactive Low-Voltage Ion Plating is studied in air and at room temperature. A multilayer stack, composed of tantalum pentoxide and silicon dioxide layers, is considered and the interactions layer to layer turn out to have no effect as regards to the final bending. Evolution in stress after annealing shows the possibility to reduce the stress as well as the absorption for tantalum pentoxide thin films. Finally, ion implementation, such as helium and xenon, at high energy, prove to be also a way to vary and diminish the stress in thin films.