The caustic of a laser beam and the associated laser beam intensity distribution (LBID)
directly affect the quality of the laser-directed energy deposition (LDED) process used
to process metal powder or wire. Existing measurement systems are typically designed
for lower-power, smaller-diameter Gaussian laser beams and are therefore unsuitable
for measuring the caustic of the annular laser beam (ALB) of large diameter and power
used in the considered LDED system. This thesis presents the design of a system for
measuring the caustic of an annular laser beam (SMCALB), based on capturing the
LBID with a CMOS camera at multiple positions along the beam path. To reduce
the beam’s power to a level the sensor can measure, the system uses a partially reflec-
tive mirror with an antireflective coating together with an optical filter. All required
optical and mechanical components were defined and selected, a 3D assembly model
was created, and the cost of the system was estimated. Expected measurement errors
were also analyzed, including the effect of double reflection and the angle dependence
of reflectivity. The designed system enables faster, simpler, and more affordable me-
asurement of the annular laser beam’s caustic compared to existing methods used at
the Laboratory for Synergetics.
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