| Popis: |
Raman scattering is a powerful instrument for spectroscopic sensing, which offers superb selectivity but typically at the expense of low signal and long collection times. In this paper we discuss mechanisms for signal enhancement that dramatically improve the performance of Raman spectroscopic systems. Several approaches, as well as their combinations are considered. One approach is to produce Raman coherence; other approaches exploit the advantages of nanosized antenna-like structures, or employ wavefront shaping of the applied laser beams. Combining these techniques in one system leads to multiplicative signal enhancement and results in an unprecedented sensitivity. In a sequence of steps toward this goal, we show that the automated feedback-based wavefront shaping algorithm is capable of improving coherent cascaded Raman scattering in crystals. In addition, we utilize the fact that specially designed nanoantennas, placed in the vicinity of the target molecule, can significantly increase the probability of exciting dipole-forbidden electronic transitions. Nanostructure-enhanced spectroscopy with shaped beams will allow for an increase in spectroscopic sensitivity and efficient detection of magnetic dipole and electric quadrupole transitions induced in molecules. The ultimate goal for developing these techniques is to achieve single-molecule sensitivity in spectroscopy, combined with atomic spatial resolution, study the layout and chemical bonds of the molecular structure and extract information relevant to chirality. |
