The light source for fluorescence excitation in confocal microscopes is a laser or a combination of lasers with varying color. Lasers are used for technical reasons . Unfortunately, traditional lasers emit usually only a single wavelength, or a few lines only (a modern solution is the white light laser ). However, the fluorochromes used in biomedical imaging show excitation bands anywhere in the spectrum between near UV and near
From Filter Wheels to AOTF
Fluorescence excitation needs specifically colored light: it should excite the probe efficiently (close to the excitation maximum) but leave room to collect the emission without spilling into the detection path. In confocal microscopy, multiline lasers or laser “batteries” are classically used. This arrangement requires devices that pick the requested lines which fit the currently employed fluorochromes. Intensity control is another task that must be accomplished – most lasers will show increased noise when intensity is controlled directly at the source. The introduction of acousto-optical tunable filters has simplified filtering and at the same time improved the flexibility significantly. For coupling white light laser sources, the AOTF is only sensible device.