Beckman Coulter LS 13 320, User Manual

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PN B05577AC xxvii
LS 13 320 Introduction
System Components
Figure 5 Module Eject and Door Open Buttons
Before a module can be docked the sample cell chamber door must be retracted. This is easily done
by pressing the
Open
button found on the left side of the optical bench ( Figure 5 ).
Light Source
The LS 13 320 uses a 5 mW laser diode with a wavelength of 750 nm (or 780 nm) as the main
illumination source. It also has a secondary tungsten-halogen light source for the PIDS system. The
light from the tungsten-halogen lamp is projected through a set of filters which transmit three
wavelengths (450 nm, 600 nm, and 900 nm) through two orthogonally oriented polarizers at each
wavelength.
Light from a laser diode is monochromatic- a requirement of the theoretical models that describe a
particle's scattering function. However, as opposed to gas or liquid lasers, the light from a laser
diode is not “focused”. The monochromatic light from a laser diode must also be “treated” to
produce a “clean” beam. The device that is most often used to condition an illuminating source is
commonly known as a spatial filter. Most spatial filters consist of a set of optical elements -
components such as lenses, pinholes, apertures, etc. - designed to refine the beam to the desired
quality.
Figure 6 depicts a mechanical spatial filter. One feature of the LS 13 320 is that it
incorporates a (patented) fiber optic spatial filter.