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@PHDTHESIS{Jung:1017937,
author = {Jung, Manuel},
othercontributors = {Häfner, Constantin Leon and Bergs, Thomas},
title = {{E}influss des {T}emperatur-{Z}eit-{V}erlaufs auf
{F}ormtreue und {W}elligkeit bei der {L}aserpolitur von
{G}las; 1. {A}uflage},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {Apprimus Verlag},
reportid = {RWTH-2025-07590},
isbn = {978-3-98555-302-0},
series = {Ergebnisse aus der Lasertechnik},
pages = {1 Online-Ressource : Illustrationen},
year = {2025},
note = {Druckausgabe: 2025. - Veröffentlicht auf dem
Publikationsserver der RWTH Aachen University. - Weitere
Reihe: Edition Wissenschaft Apprimus; Dissertation,
Rheinisch-Westfälische Technische Hochschule Aachen, 2025},
abstract = {For laser polishing of glass, the glass surface is heated
using CO2-laser radiation, and in the resulting state of
reduced viscosity, a redistribution of material is achieved
through the inherent surface tension. For laser-polished
glass surfaces a roughness comparable to that of commercial
optics is already achievable. In addition, the process times
– especially for aspheres and freeform optics – are
significantly shorter than with mechanical polishing.
However, the industrial application of laser polishing of
glass is still limited due to form deviations and waviness
on the polished surfaces. Therefore, this work aims to
develop an understanding of the influencing factors behind
these errors by investigating the temperature-time profile
of the overall process, consisting of preheating, laser
processing, and annealing. The primary cause of the form
deviation is found to be the homogeneity of heat input
during the preheating process. By adjusting the preheating
process, a significant reduction in shape distortion to a
level comparable to commercial aspheres is demonstrated for
N-BK7. The waviness after laser polishing can be separated
into induced (caused by the laser polishing process) and
residual (insufficiently smoothed) components. For fused
silica, a temperature-dependent removal process is observed
even below the evaporation temperature. Due to fluctuations
in the process temperature, inhomogeneous ablation occurs
and as a result a waviness-like structure is induced into
the glass surface. By using a PID-based process control, the
induced waviness can be reduced, but not fully avoided. As
the reduction of existing structures is also determined by
the viscosity of the glass and thus by the process
temperature, a trade-off between induced and residual
waviness is inherent for laser polishing. As a result, when
implementing laser polishing in production, it is necessary
to evaluate the laser polishing process in the context of
the full process chain. Based on these findings and using
the two materials N-SF6 and S-FPL53 as examples, a procedure
for transferring laser polishing to other glass types is
developed. Finally, the effect of laser polishing on
sub-surface damage induced by the form generation process is
addressed. In laser polishing, whenever a polishing effect
can be observed, the healing depth of SSD already exceeds
the maximum observable SSD depth after grinding. For
example, for fused silica, depending on the laser
parameters, a safety factor of up to 40 is achieved. Thus,
the feasibility of laser polishing of glass with shape
accuracy and surface qualities comparable to commercial
optics is demonstrated. In addition, insights into the
technical requirements for the next generation of laser
polishing systems are given.},
cin = {418710},
ddc = {620},
cid = {$I:(DE-82)418710_20140620$},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.18154/RWTH-2025-07590},
url = {https://publications.rwth-aachen.de/record/1017937},
}
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