The study purpose is to highlight dental hard tissues changes of a tooth with dental wear as a consequence of excessive occlusal forces, using OCT. Methods: a central incisor extracted for periodontal reason was cleaned and it was embedded in a black acrylic resin block. The block was sectioned along the longitudinal axis of the tooth and prepared for OCT analysis. Results: The OCT signal showed differences between the labial and palatal dental hard tissue structures, even in areas without excessive occlusal solicitations. Conclusion: The OCT signal highlights changes of dental hard tissues structures according to excessive occlusal solicitations areas.
There are several important non carious lesions affecting the tooth structure, lesions which may be classified into four clinical forms of dental wear: abfraction, erosion, attrition and abrasion, and different types of root resorption. Search for new, non-invasive and fast methods able to detect and describe such injuries is of utmost importance. Optical coherence tomography (OCT) proved itself as an appropriate investigation method for several medical fields including ophthalmology, dermatology, cardiology etc. Our study reveals OCT preliminary investigations as a promising tool for detecting and evaluating of the mentioned lesions.
The garnets with disordered structure such as calcium niobium gallium garnet (CNGG) doped with Nd3+ are interesting materials for diode pumping. Spectroscopic investigations on Nd3+:CNGG have revealed a multisite structure and this is reflected in laser emission characteristics. The purpose of this paper is to present several new spectral aspects, a modeling for the main nonequivalent centers, energy transfer characteristics and an attempt to connect the laser characteristics to centers structure. Samples were grown by Czochralski method with Nd3+ from 0.1 to 5 at.% and the high resolution spectral and decay measurements were performed at 10 K. Similar considerations were made in the case of Nd3+ doped in calcium lithium niobium gallium garnet (CLNGG).
The paper discuses the influence of cross-relaxation parameter on the characteristics of the sensitized photon avalanche. A system Pr3+ as activator ion and Yb3+ as sensitizer ion were considered for the avalanche process. By numerical modelling of a system of rate equations, time dependencies and pump rate dependencies of populations of energy levels were calculated for three different values of cross-relaxation rate. Correlation between cross-relaxation rate and threshold value of pump intensity was established.
An analysis of low temperature lineshapes for various absorption lines of several RE3+ ions from the beginning Nd3+ and end of lanthanide series Er3+, Tm3+ embedded in the same crystal - YAG known as important laser systems for 1-3 micrometers emission is presented. New aspects of the dependence of electron-phonon coupling on RE3+ ions and matrix are observed from the analysis of many transitions of these ions at low temperature. These data show that eh electron-phonon coupling presents a symmetric behavior in the lanthanide series, larger toward beginning and end. With only very few exceptions, less than 2 percent, the broadenings or splittings of zero-phonon liens could be connected to optical Raman phonons of undoped lattice. That means that the parity of 4fn states could still be considered a good parent quantum number, even if the local symmetry has no inversion, and the near resonant coupling involves the even part of the electron-phonon coupling operator. Besides, the one phono relaxation involve the undoped lattice phonons. For ions with small spin-orbit coupling, the vibronic contribution to the line intensity given by ir phonons through a Van Vleck mechanism could be important for spin forbidden transitions.
Laser crystals with disordered structure present a series of advantages for diode pumping or short pulse generation as compared with ordered crystal. Such a system proved to be calcium lithium niobium gallium garnet (CLNGG) doped with Nd3+. The papers present the growth and x-ray analysis of specially doped CLNGG. Very few spectroscopic data on this system have been previously published. The paper present low temperature absorption spectra, site selective excitation and lifetime measurements of Nd3+ in CLNGG. At least four distinct nonequivalent centers are observed, the spectral lines for every center presenting a disordered Gaussian shape. based on structural, spectral static and emission dynamics data an attempt of modeling the structure of these centers is proposed.
The paper discusses the effect of pump intensity variations caused by absorption in a fiber system with upconversion avalanche fluorescence or laser emission. The numerical modeling shows that in given pump conditions the initial part of the fiber (up to a distance zth) is pumped above the avalanche threshold while the remaining part lies below it. This induces a strong variation of populations of the excited levels along the fiber. The characteristics of the avalanche emission are connected to the spectroscopic parameters of the system and to the conditions of pump. It is also shown that the features of the global luminescence emission at the end of fiber depend strongly on the fiber length for the short fibers (L <EQ zth) but for the long ones this dependence diminishes; thus the avalanche emission of a long fiber could be different from that predicted by a constant rate modeling. The effect of distribution of local pump intensities on laser emission in avalanche-driven upconversion fiber lasers is also discussed.
The features of a new upconversion mechanism of excitation, the sensitized photon avalanche, are discussed on the basis of a rate equation modeling. In this process the excited state absorption (ESA) from a metastable level (reservoir) of the active ion is enhanced by a cross-relaxation between the emitting level of this ion and the sensitizer ion which is able to transfer subsequently the accepted excitation back into the reservoir level of the activator; the donor act of the cross-relaxation ends on this reservoir level too. When the efficiencies of these two energy transfer processes are larger than specific threshold values related to the intrinsic de-excitation rates of the emitting level of activator and of the excited level of sensitizer, a process of population of the reservoir level with a quantum efficiency larger than the unit for each act of de-excitation of the emitting level takes place. Further on, if the ESA rate exceeds a threshold value determined by the intrinsic de- excitation of the reservoir and by the efficiencies of the energy transfers an avalanche population of these levels could take place. This process could be used for infrared pumping of visible solid state lasers. The theory is illustrated for Yb3+- sensitized visible emission of Pr3+ under infrared pump (835 nm).