There is a growing demand for non-spherical glass optics. Currently,
these optical elements – for example lenses for cameras or
multifocal glasses – are still very costly to manufacture. The
Fraunhofer Institute for Laser Technology ILT has developed a process
for manufacturing optical glass components, which should be
particularly suitable for the cost-effective production of aspheres and
free-form optics. With this procedure, engineers will be able to
produce nearly every surface geometry imaginable in the future.
In optical systems such as headlights, projectors, camera lenses and
lenses for glasses, optics ensure that light is focused as well as
significantly determining image quality due to their surface form and
finish quality. With commonly used spherical optics, the risk of
aberration typically is reduced through combining several optics in a
single optical system. However, this approach also increases the weight
and size of the optical system. By using non-spherical lenses, whose
surface form deviates from the spherical curvature of a spherical lens,
engineers can effectively minimize such aberrations. This way, two or
more conventional spherical optics can be replaced by one asphere and
enable higher luminous efficacy. In addition, the dimensions and the
weight of the overall optical system can be reduced.
Until now, small quantities of non-spherical optics have been produced
through a number of expensive and time-consuming grinding and polishing
steps. While the blank pressing of optics represents one possible
alternative, it, however, is only economical for larger quantities. A
young research team at the Fraunhofer ILT has developed a new process
for individual manufacturing of apheres and free-form optics within the
scope of the project “Forming and Polishing of Optical Glass
Components by Ablation and Remelting with Laser Radiation” (or
FoPoLas).
Ablating, Polishing, CorrectingSebastian Heidrich and his team have been able to produce non-spherical
and free-form surfaces with different degrees of curvature out of a
quadratic piece of fused silica. In order to do this, they have
combined different processing techniques into one process chain:
Firstly, a CO2 laser beam heats the material to over 2,230°C, the
evaporation temperature of fused silica. This way, the unnecessary
material is evaporated selectively and ablated. According to computer
generated data, nearly any surface form desired can be produced. In a
following step, CO2 laser radiation heats the surface of the component
again to near the evaporation temperature so that the viscosity of the
uppermost material layer is changed. It becomes fluid and its roughness
is reduced on account of the surface tension. The material remains
polished once it has cooled. After this laser polishing step, remaining
form defects shall be corrected with laser-based precision ablation in
the future.
High Economy also for Small Series ProductionThis process chain is directed primarily at manufacturers of
individualized, non-spherical optics. Since the desired surface form is
produced based on computer data, it can be changed without extensive
retooling. In comparison to conventional manufacturing methods, the use
of this process chain could shorten the time it takes to produce
optical glass components presumably by a factor of ten. For complex
free-form surfaces, this factor can even be much higher. This would
mean an enormous reduction in costs and high flexibility for the
production of small to medium lot sizes. The process steps can also be
used separately, for example, to polish the inside of drill holes,
starting from a diameter of several millimeters.
Currently the scientists are optimizing the individual steps of the
process chain. Before the process can be applied in the industry, the
precision of the ablation process and the surface quality of the
polishing process have to be increased. In addition, an appropriate
measurement technology has to be developed for form detection, in order
to attain suitable optical quality of the manufactured glass components.
On May 11, experts will be presenting the process within the scope of
the International Laser Technology Fair AKL’12 in the laser plant
park of the Fraunhofer ILT. Interested parties can find further
information on this at: www.lasercongress.org
More information at
www.ilt.fraunhofer.de/
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