Figure 12.

Left: ilumination unit of the microspectrophotometer MS3. The unit is a combination of a Köhler-type microscope light and a light guide coupled to an absorption spectroscopy broadband white-light source. A 190 mm vertical translation with a 1 µm resolution permits the unit to be retracted within 2 s. Lateral positioning is provided by the vertical translation and a second horizontal stage (range 10 mm, resolution 1.25 µm). Right: beam paths in the MS3 illumination unit. The vertical beam path of the Köhler illumination comprises (from bottom to top) an LED light source, two lens doublets, an iris to define the illuminated area, a polarizer, a third doublet and a reflective objective. The beam path of the spectroscopic illumination contains the fiber holder, an off-axis parabolic mirror and a beam splitter to couple the light into the reflective objective along with the Köhler illumination branch.