Scattering losses, lasers

Raman spectroscopy is based on the inelastic scattering of laser radiation with loss of vibrational energy by a sample. A vibrational mode is Raman-active when there is a change in the polarizability during the vibration. Symmetric modes tend to be Raman-active. For example, vibrations about bonds between the same atom, such as in alkynes, can be observed by Raman spectroscopy. 

The infrared lasers have the advantage that the contribution of scattering losses to the total beam attenuation is much smaller than in the visible range. For measurements of very low concentrations, on the other hand, visible dye lasers may be more advantageous because of the larger absorption cross sections for electronic transitions and the higher detector sensitivity. 

Finally, alternate forms of substrate pumping were considered in some detail. The energy escape fraction is largest from small spheres of uranium metal or oxide. Such spheres carmotbe incorporated directly into the laser medium because of the optical scattering loss they introduce, even if they were overcoated with a thin reflective coating. However, concepts have been developed to use such reflective aerosols to pump a fluorescer medium, which produces intense incoherent light usable for optically prrmping a laser medium. 

Figure Pl.l Conceptual laser resonator, including optional components for wavelength selection and temporal shaping of the laser output. Intrinsic photon loss processes, which reduce the useful laser radiation absorption, spontaneous emission and non-radiative losses in optical media scattering losses at resonator components imperfect reflection/ antireflection coatings...

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