Raman confocal setup

Furthermore, in the electrochemical system, most of the electrolytes are corrosive, and to protect the objective, a cover glass or quartz window has to be employed between the electrolyte and the objective, this results in 50% loss of the signal. An alternative way to protect the objective is to wrap it with a very thin and highly transparent polyvinyl chloride (PVC) film. A benefit of the confocal setup is that there is no signal from PVC in this configuration. By this approach, the Raman signal only suffers 20% loss. The disadvantage of this approach is that without the quartz window, the solution has to be exposed to the air, and impurities in the air wQl contaminate the solution. For systems that are very sensitive to any contamination, a thin quartz window, with thickness of 0.2 to 0.5 mm, has to be employed at the cost of the intensity. 

Figure 7.3 Confocal setup for Raman microspectroscopy. Holes D1 and D2 are optically conjugated.

With the help of a micro-Raman setup the laser spot can be focused down to about 1 pm in diameter. This allows for the differentiation of single bacterial cells or a biochemical analysis of subcellular components within bacterial (diameter approx. 1 pm) or yeast cells (diameter approx. 5-10pm). A confocal Raman setup achieves an even better spatial resolution [6, 7]. This possibility enables Raman mapping or imaging experiments with spatially resolved information of the whole sample in axial and lateral directions. 

Caspers et al. [31] developed a confocal Raman setup for in vivo measurements of skin (Fig, 9). The instrument has a depth resolution of about 5 )am and therefore allows different layers in the skin, such as stratum corneum, living epidermis, and dermis to be investigated separately (Fig. 10). 

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