Programmable Illumination and High-Speed, Multi-Wavelength, Confocal Microscopy Using a Digital Micromirror
Figure 1
Schematic diagrams of the DMD confocal optical pathway and the mirror arrangement for pinhole formation and scanning.
A. Light from the excitation source was expanded and collimated and sent to the DMD via a dichroic mirror. Mirrors in the “on” position on the DMD send the excitation light through a tube lens to the microscope objective and the specimen. Light emitted from the specimen travels back along the same path but it then passes through the dichroic mirror (Dchr). An emission filter (Em) ensures that only the desired excitation wavelength can reach the camera. A modified Offner Triplet arrangement consisting of three separate curved mirrors (CCv1 and CCv2 concave mirrors, r = 207; Cvx convex mirror, r = 103.5) and a single plain mirror (Pm) were then used to form an image on the CCD of an EM camera positioned at a second conjugate image plane. The double-headed arrow next to CCv2 illustrates the approximate plane of movement that allows a change in the magnification of this optical relay. B. A scanning unit consists of n×n micro mirrors in the “on” position, acting as a pinhole, in a square of p×p pinholes. Full scan of the unit is obtained by presenting a series of p2 scanning units with the pinhole in different positions. Different values of n and p define different configurations, referred to as “n×p”, and give different levels of confocality. The figure illustrates a 2×4 confocal configuration.