Lasers, optical centers study

The study of optical centers in solids, liquids, and molecules has fascinated many scientists over a range of years. However, not only scientific curiosity has pushed forward this type of spectroscopy. Simultaneously, many possible applications became clear. The first solid state laser was based on a ruby crystal. Also, in the development of tunable infrared lasers the Cr " " ion played an important role. 

When designing a new solid state laser system, an appropriate choice of the matrix - active center combination is needed. On the one hand, the active center should display optical transitions in the transparency region of the solid, which consequently requires the use of wide-gap materials. Additionally, the transitions involved in the laser action should show large cross sections in order to produce efficient laser systems. This aspect, which is directly related to the transition probability, is treated in depth in Chapters 5 and 6, where the physical basis of the behavior of an optically active center in a solid is studied. 

The luminescence of diamonds is related to various defects in its structure. Almost always, luminescence centers in diamonds are related to N atoms. It is logical, because the atomic radii of C and N are nearly equal (approximately 0.77 A). Luminescence spectroscopy has proven to be the most widely used method in studies of diamonds even in comparison with optical absorption, ESR, IR and Raman spectroscopies. Himdreds of spectra have been obtained, fluorescence characteristics enter into diamond quality gemological certificates, a wide range of electronic and laser applications are based on diamond optical properties in excited states nitrogen center aggregation is controlled by the residence time of diamond in the mantle, distinction between natural... 

Eli Y2O3 nanolayers coated on different dielectric nanoparticles Recently, the structural and optical properties of Eu3+ Y2C>3 films coated on a variety of dielectric nanoparticles have been investigated using transmission electron microscope (TEM), X-rays diffraction (XRD) and site-selective laser spectroscopic methods (Chen, X.Y. et al., 2005 Chen et al., 2003a). Eu3+ ions are employed as probes for the study of crystallization and multi-site structure as well as the luminescent centers in nanolayers. It was found that the luminescent nanolayers exhibit distinct thermodynamics and luminescence properties. 

Figure 1. UV field illumination of a Plan Apo 100x lens (1.4 NA) derived with a fluorescent plastic slide and the intensity measurement of 10-micron Spherotech beads (obtained from Spherotech, Libertyville, IL, USA). This illustrates the problem of using a lens with improper field illumination to make comparative measurements on a sample. The field illumination pattern shows a bull s eye intensity pattern slightly off-center and the five beads located in different parts of the field to illustrate the variation in intensity occurring by using a lens that has improper field illumination. The intensity of beads was derived by a small Region of Interest (ROI) inside the bead. The five beads show a decrease in intensity relative to the bead in the center of the illumination. Although this figure was obtained with UV optics, it represents the type of field illumination that can also occur with visible light excitation. This pattern is also unacceptable, if a confocal laser scanning microscope optical system is used for a FISH study, as the maximum intensity should be in the center of the objective and not in the corner.

Tanaka and Benedek (1974), in a novel and important study, have measured the velocity of blood flow in the femoral vein of rabbit by detecting (in the heterodyne mode) the Doppler shift of laser light introduced into the vein by means of a fiber optic catheter. The light is scattered from the moving erythrocytes in the blood. It is important to recognize that the blood-flow velocity is not uniform across a vein but varies from zero near the vein wall to a maximum in the center. Thus the spectrum observed should be an average over the distribution of velocities of the illuminated erythrocytes, approximately... 

While the use of direct absorption methods has grown, indirect action spectroscopic methods continue to be widely and successfully used in the study of neutral molecular clusters. As mentioned earlier, there are two commonly used detection methods, mass spectrometers and bolometers. Because of the variety of mass-spectroscopic methods, there is an equally wide range of techniques used in neutral cluster spectroscopy. One of the oldest among these involves electron-impact mass spectrometry of a cw neutral beam combined with vibrational predissociation spectroscopy using a tunable cw or pulsed laser. The advent of continuously tunable infrared sources (such as color center lasers and LiNbOa optical parametric oscillators) allowed for detailed studies of size and composition variation in neutral clusters. However, fragmentation of the clusters within the ionizer of the mass spectrometer, severely limited the identification of particular clusters with specific masses. Isotopic methods were able to mitigate some of the limitations, but only in a few cases. 

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