Adaptive Optics for Vision Science

Chapter 10.3.4 - Light Delivery

10.3.4   Light Delivery

It is important to start with a point source or a well-collimated beam in order
to focus a beam onto the retina. The light source in an SLO generally originates
from a spatial filter pinhole or from a single-mode optical fiber. Fibers
are convenient because hardware fixtures are readily available that allow
them to be switched (e.g., for different wavelengths) without requiring any
new alignment. The point source can be collimated and propagated into the
imaging system. The type of light source and the wavelength depend on the
imaging goals. Chapter 9 talks about how different wavelengths reflect from
the retina.

Because these systems are highly confocal and the sampling is very fine,
speckle can generate unwanted noise into the images. For that reason, a low
coherence light source may be a better choice for the light source. Preliminary
testing of low-coherence light sources is currently underway.

To minimize any unnecessary exposure to the retina, it is advised to modulate
the laser beam so that the retina is only exposed when image pixels are
being acquired. To control the beam, the laser can be modulated directly, or
an acousto-optic modulator can be placed in the light delivery path (outside
of the double-pass optical path) to turn the beam on during the forward part
of the horizontal scan and off on the return.

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