Laser-self-mixing interferometry in the Gaussian beam approximation: experiments and theory.

We analyze the laser-self-mixing process in the Gaussian beam approximation and reformulate the expression of the feedback coefficient C in terms of the effective feedback power coupled back into the laser diode. Our model predicts a twenty-fold increase of the ratio between the maximum and the minimum measurable displacements judged against the current plane-wave model. By comparing the interaction of collimated or diverging Gaussian laser beams with a plane mirror target, we demonstrate that diverging beams tolerate larger wobbling during the target displacement and allow for measurement of off-axis target rotations up to the beam angular width. A novel method for reconstructing the phase front of the Gaussian beam by self-mixing scanning measurements is also presented.

[Structure of alveolar bone during tooth eruption in the dog: preliminary findings]. / La struttura dell'osso alveolare durante l'eruzione dei denti nel cane: dati preliminari.

The structure of the alveolar bone during the tooth eruption in the young dog mandibles was investigated by microradiographic and polarized light techniques. Around the first erupting molar root a trabecular network of primary alveolar bone, less mineralized than the surrounding cortical one, was found. Numerous calcified spicules parallel one to others radiate out the spongiosa near the periodontal ligament. The collagen fiber bundles of the alveolar, woven, bone are continuous with the periodontal ligament ones. This finding indicates that the alveolar bone increases by ossification of the periodontal ligament. Therefore the latter is the forming alveolar bone substratum. The trabeculae of the occlused premolar alveolar bone are ticker and more mineralized. This modification of the occlused tooth alveolar bone could be related to the occlusal stresses.