DOC-0171 Rev G-9
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© 2017 DROPLET MEASUREMENT TECHNOLOGIES
Figure 4 details the YAG laser, the optical configuration for SP2, and the optical detectors. The YAG
laser is central to the system, with the four detectors being seen as in the plane of the page. The
aerosol jet is perpendicular to the plane of the page and sends the particles across the laser beam.
Figure 4: SP2 Optical Diagram
2.2 Optical Detectors
Four optical detectors are used. One detector is optically filtered to pass only the 1064 nm
radiation. This will measure the scattering signal from all particles, both those that scatter light
only, and those that absorb light and both scatter and incandesce. This detector is identified as
Channel 0 in the data. Two photomultiplier tube (PMT) detectors measure the incandescence signal
in the visible region. These channels are optically filtered to pass broadband light, nominally from
400-650 nm and narrow-band light, nominally from 610-650 nm. These are identified as channels 1
and 2 in the data, respectively. The ratio of the signals from these two detectors allows the color
temperature of the incandescing particles to be calculated, providing assurance that the particle
measured is elemental carbon. A fourth detector allows measurement of the leading edge of the
scattering signal. This can be used to analyze the amount of coating or mixing state of the
incandescing particle. Details on this analysis are given by Gao et al. (2007). This is Channel 3 in the
data.