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Paper des Monats
- ja (1)
Functionality of optical systems requires optical coatings of
high quality which have to be adapted to the application in
terms of the performance of optical parameters such as
reflectivity (AR, low, defined, high), the substrate material of
interest (polymers, ceramics, and glass), the environmental
conditions (such as temperature or humidity), and the service
conditions (such spectral range and power density). Moreover,
in many cases, additional non-optical requirements have
to be met, including mechanical features such as scratch
resistance, hardness and modulus.
Consequently, thickness and overall uniformity requirements
are steadily increasing. In general, these demands can usually
not be achieved by a single film or coating. Instead, films with
specific design features (such as gradients), layer stacks and
multilayers are a prerequisite for high quality layers and their
reliability. For the development of such layer systems, a
versatile cluster deposition system consisting of three clusters
and a cluster-to-cluster handler has been designed. Besides a
PECVD cluster for DLC coatings, two PVD clusters implement
ion assisted electron beam evaporation and plasmabased
sputter technology. In addition to metallic films, preparation
of oxide and nitride optical coatings (SiO2, TiO2, Ta2O5,
ITO, Al2O3, TiN, AlN) in various process modifications (nonreactive,
partially reactive, full-reactive; rf-, dc-, mf- mode;
PEM control) has been carried out.
Within this paper, the effect of several process parameters on
layer quality (optical constants, density, and uniformity) is
discussed for selected applications examples (AR- and HR
coatings, applications at elevated temperatures and applications
of enhanced mechanical performance).
It has been shown that specific features of ion and plasma
assisted PVD processes, including ion-beam and plasma preand
post-treatment of substrates and layer systems, may
widen the application range and improve functionality features
of given coating/substrate systems.
Surface damage and color centers generated by femtosecond pulses in borosilicate glass and silica
(2003)
Femtosecond laser pulses are close to industrial use. The advantages of ultrashort laser pulses for micromachining applications especially in the case of dielectric and biological samples down to pulse durations of 5 fs have been established. The current international standards of laser safety are primarily concerned with CW and pulsed lasers down to the nanosecond range. Therefore, human tissue and laser-protection equipment was investigated with respect to its resistance and protection performance for femtosecond laser illumination down to 30 fs. This included filter glasses for laser protection eyewear, polymer and textile materials used in curtains and guards. Bulk absorber filters can provide enough protection against laser radiation, give a sufficiently broad absorption spectrum. Materials are damaged more easily by femtosecond laser radiation. The need for sufficient spectral broadness as well as the different damage thresholds have to be included in international laser safety standards. This work should trigger the development of novel eye-protection devices that are lighter and ergonomically more acceptable than present commercial models.
Results of a round-robin experiment in multiple-pulse LIDT measurement with ultrashort pulses
(2004)
The multi-pulse ablation threshold of barium borosilicate glass was measured using 30-fs pulses of a high repetition rate (1 kHz) laser system. The threshold fluence was found to decrease with increasing beam radius ranging from 20 to 400 m. Two existing models are applied by considering thermal accumulation and point defects, respectively .