Characterization techniques - Micromixers Fundamentals Design and Fabrication - page 301

FIGURE 8.5

Schematic concept of a confocal laser scanning microscope with two pinholes and a scanning stage.

Stage scanning has the advantage of simplicity. The beam is stationary and the objective is used on
axis. Thus, aberration correction is easy. However, the scanning speed is limited by the relatively large
weight of the scanning stage. Most commercial confocal microscopy systems use beam scanning
techniques because of their speed advantage. Scanning in x - and y -direction is realized by combining
beam-steering devices, such as galvanometer mirrors and acousto-optic deflectors. Using an x -slit
instead of the pinhole, a CCD line array can be used for recording the image line by line. If the x -line
image is descanned by a y -scanning mirror, an apparent two-dimensional image can be generated and
observed by eyes or recorded by a two-dimensional CCD sensor.
Direct-view confocal microscope can also be realized by the rotating Nipkow disk, which was
originally used for mechanically scanned television. Figure. 8.6 shows the schematic concept of
a real-time scanning optical microscope. The pinholes in the disk are used for both illumination and
imaging. The disk is tilted slightly by about 5 . The tilted disk reflects light away from the eyepiece.
Further, an optical insulator also deflects a part of light reflected from the top of the disk back to the
light source.
The disk has several thousand pinholes arranged in interleaved spirals. Several hundred pinholes
are illuminated at the same time, in order to increase the light efficiency and scanning speed. With this
disk design, a rate of several hundred frames per second and several thousand lines per frame can be
achieved. The pinholes on the disk are fabricated using photolithography techniques as discussed in
Chapter 4. The typical pinhole size is about 20 m m.