The current status of UV-damage in several different UV fibers due to defects in their synthetic high-OH silica core and cladding will be described. Further, steps to improve UV resistance and adequate measurement techniques based on a deuterium lamp setup are included. For the first time, the main parameters and their influences on UV induced losses are discussed in detail with an emphasis towards future standardization purposes. Applications based on two new UV light sources, a laser driven xenon plasma broad band source and a high pulse-power 355 nm Nd:YAG laser, are introduced. UV photo-darkening and -bleaching in UV fibers caused by this extremely
powerful light source is demonstrated. Finally, first results on transmission of UV light in optical fibers at cryogenic temperatures are shown.
High-order skew modes will be excited in multimode step-index fibers using special excitation conditions. As a result, light
with an angle of incidence larger than the maximum angle for meridional modes given by the numerical aperture
of the fiber can be coupled into a fiber. Combining the selective mode-excitation with new powerful broadband light-sources,
the spectral light-guidance of such skew modes in different optical fibers will be described in detail. Results of the proposed
system in context of different light-sources will be discussed. A new evanescent sensor approach based on controlled
coupling of skew modes will be introduced. Finally, first steps to construct such sensors for medical and analytical
applications will be presented.
Physical and optical properties of optical fibers have improved over recent years significantly. Especially classic UV
detection techniques in traditional chemistry, HPLC and dissolution testing rely more and more on fiber optic light
guiding techniques to transport light to and from a sample simplifying the design of such detection techniques. An
overview on the current status of UV-fiber optical properties will be given in this work. Especially, the reduction of UVdefects
in the 215 nm wavelength region leading to a lower drift in the whole system, will be discussed.
However, these are not the only parameters of interest in a fiber-optic system. For process control or instrumental
analytics, the long-term stability including drift and noise must be determined. This requires stringent fiber test
procedures similar to light-sources, connectors and complete detector systems. Further, white-light interference between
optical interfaces of a fiber optic detection system due to axial movement, degradation of components and temperature
often reduces system stability and must be considered. Finally, a cleaning-in-process of a fiber optic immersion probe will be introduced as a further step of system improvement.
UV solarization resistance of synthetic silica/silica fibers has been researched over many years. Fiber optic probes for
applications as diverse as protein analysis, dissolution testing or high pressure liquid chromatography have been
developed and successfully commercialized. Although fabrication technology for optical fibers has improved
significantly and optical losses due to solarization effects have been minimized in synthetic silica fibers, the generation
of UV induced defects in silica fibers due to the generation of E'centers visible in the 215 nm region is still present and
can interfere with sensitive spectroscopic absorbance measurements. This work presents methodology to determine the
transient response of optical fibers in the 200 nm to 300 nm region during the warm up period and during measurement
as a function of light power coupled into the fiber, fiber length and fiber diameter.
Previous studies of the hyphenation of gas chromatographic separation and spectrophotometric detection in the
ultraviolet wavelength range between 168 and 330 nm showed a high potential for applications where the analysis of
complex samples is required.
Within this paper the development of a state-of-the-art detection system for compounds in the vapour phase is
described, offering an improved behaviour compared to previous systems:
Dependent on the requirements of established detection systems hyphenated with gas chromatography, the main
components of the system have to be designed for optimum performance and reliability of the spectrophotometric
detector: A deuterium lamp as a broadband light source has been selected for improved stability in the measurements. A
new-type absorption cell based on fiber-optics has been developed considering the dynamic necessary to compete with
existing techniques. In addition, the influence of the volume of the cell on the chromatogram needs to be analyzed. Tests
for determining the performance of the absorption cell in terms of chemical and thermal influences have been carried
out. A new spectrophotometer with adequate spectral resolution in the wavelength range, offering improved stability
and dynamic for an efficient use in this application was developed.
Furthermore, the influence of each component on the performance, reliability and stability of the sensor system will be
discussed. An overview and outlook over the potential applications in the environmental, scientific and medical field
will be given.
In thin-layer chromatography, fiber-bundle arrays have been introduced for spectral absorption measurements in the
UV-region. Using all-silica fiber bundles, the exciting light will be detected after re-emission on the plate with a fiberoptic
In addition, fluorescence light can be detected which will be masked by the re-emitted light. Therefore, it is helpful to
separate the absorption and fluorescence on the TLC-plate. A modified three-array assembly has been developed: using
one array for detection, the two others are used for excitation with broadband band deuterium-light and with UV-LEDs
adjusted to the substances under test. As an example, the quantification of glucosamine in nutritional supplements or
spinach leaf extract will be described. Using simply heating of the amino-plate for derivation, the reaction product of
Glucosamine can be detected sensitively either by light absorption or by fluorescence, using the new fiber-optic
In addition, the properties of the new 3-row fiber-optic array and the commercially available UV-LEDs will be shown,
in the interesting wavelength region for excitation of fluorescence, from 260 nm to 360 nm. The squint angle having an
influence on coupling efficiency and spatial resolution will be measured with the inverse farfield method. Some
properties of UV-LEDs for analytical applications will be described and discussed, too.
The precise analysis of potential hazardous components within gases and the detection of trace gases in exhaled breath for early and non invasive diagnosis of illnesses have a great influence on the well-being of human beings. Besides the existing analysis techniques, which mostly require sample preparation, costly consumables, huge space and skilled personal carrying out the measurement, a measurement system based on optical absorption in the UV wavelength region might offer alternatives to existing techniques. Within this work a feasibility study based on measurements of different test gases at lowest concentrations and requirements for trace gases in exhaled breath in respect to detection limits, signal-to-noise ratio and system drifts were analyzed. A spectral database including over 1000 UV vapor-phase spectra allows the identification of unknown compounds within a mixture, as well as expanding the use of the measurement technique into new areas of application, for example
Based on measurements of different test gases at lowest concentrations and a spectral database including over 1000 UV vapor-phase spectra, the status of the research towards a fiber-based UV gas-analyzing equipment is reported.
For medical and analytical applications, thick-core fibers based on synthetic silica are widely spread. In many cases, the fibers are used as a light-guiding medium only; therefore, the coupling efficiency between the light-emitting area and the accepting fiber is of great importance described easily by the light acceptance cone related to the numerical aperture of the fiber. In the past, all-silica fibers with un-doped silica core and fluorine-doped silica cladding have been used for different applications. However, these fibers are restricted in respect to a low numerical aperture of typically 0.22. To increase the numerical aperture, different polymers can be used for cladding material. In addition to standard polymers, Teflon-AF is an attractive candidate for significantly higher NAs of approx. 0.65. In parallel, a new class of all-silica fibers was developed with high NA, the so-called “Air-clad” or microstructured fibers. Longitudinal microstructured holes, in the order of the wavelength, form the cladding-region together with the surrounding silica. The dimensions of the microstructure dictate the critical angle for light transmission in the core, rather than the refractive index of the cladding material. The light guiding properties of different fibers will be compared. Especially the optical transmission from the UV-region up to the NIR-region will be discussed. Due to the wavelength-dependent mean value of the refractive index (RI) in the cladding, the definition of numerical aperture has to be adjusted. Especially, the UV-damage within Teflon-coated fibers and the microstructured fibers will be described in detail.
For astronomical applications, different types of step-index all-silica fibers with high-transparency in the whole spectral region from UV (300 nm) to NIR (1100 nm) will be introduced. The light-guiding core-material consists of high-purity silica, especially with low or medium OH-content. In UV region, the losses are mainly influenced by Rayleigh scattering, while the losses in the IR region are limited by traces of OH-groups (in the order of approx.
2 ppm) and fundamental vibration-bands. Due to processing, typical UV-defects below 280 nm can be suppressed significantly within fibers with medium or low OH-content. Especially, one fiber-type with low-OH content in the core possess high resistance against UV radiation in the DUV-region down to 200 nm, which is comparable to high-OH all-silica fibers specially developed for UV-application below 250 nm. In addition, a medium-OH will be presented. The properties of these new fibers in respect to basic attenuation and spectral damage in the UV-region will be discussed, in comparison to high-OH fibers, based on the same measurement-technique. In addition, first results on focal ratio degradation (FRD) and additional loss related to higher propagation angles will be shown, in comparison to standard high-OH fibers.
In the deep ultra-violet (DUV) and the mid infra red (MIR) regions of the spectrum, the so-called Hollow Core
Waveguide (HCW) is an alternative for light-delivery systems. In addition to efficient light transportation, the HCW can
be used as an intrinsic sensor: due to the long path-length through the HCW the spectral absorption of the gas under test
can easily be monitored. Based on preliminary studies, the UV-region from 170 nm up to 250 nm seemed to be a very
attractive alternative for gas-analyses, in comparison to the IR-region with the well-known gas-absorption bands. Using
improved and adjusted components, the existing system for UV-spectroscopy was optimized. The new system will be
described in details. Especially, the time-response using an external gas-feeding system is an additional parameter of the
studies. Within the spectral range of the new CCD-array spectrometer from 175 to 210 nm, highly structured spectra
have been determined, with a spectral resolution of less than 50 pm. In nitrogen, selected gases with extremely low
concentrations in the order of 1 ppm have been measured; the absorption spectra are compared to those from IR
measurements, using the HCW approach, too.
In the deep ultra-violet (DUV) and the mid infra red (MIR) regions of the spectrum, the so-called hollow core waveguide (HCW) is an alternative for light-delivery systems. In addition to efficient light transportation, the HCW can be used as an intrinsic sensor: due to the long path-length through the HCW the spectral absorption of the gas under test can easily be monitored. Within this study an experimental system for gas analysis was developed and the results are compared to those from IR absorption measurements, also using the HCW approach.
Since more than 2 decades, the polymer optical fiber (POF) based on PMMA is well known. A lot of applications were studied and initiated: in addition to data transmission, the automotive, lighting and sensor applications are of main interest. Due to the spectral attenuation and applications, light-sources like broadband metal-halide lamps and halogen lamps, or LEDs and laser-diodes are mainly used. Due to improvement in manufacturing of the standard step-index POF, the variations of the spectral attenuation in the blue region have been reduced. Therefore, the losses are acceptable for short-length applications in the UV-A region. Using different light-sources like high-power Xenon-lamp, deuterium-lamp or UV-LEDs, the UV-damage is an important factor. In addition to the basic attenuation, the UV-induced losses will be determined by experiment, in the interesting UV-A region. The higher flexibilty of the thick-core POF is superior in comparison to silica or glass fibers with the same outer diameter. Therefore, the bending losses in the UV-region are important, too. For special applications in the medical field, side-illuminating fibers are highly accepted. The axial and spectral dependence on the lateral radiation pattern will be described, using a very thick fiber.
In the DUV-region and MIR-region, the so-called Hollow-Core-Waveguide is an alternative for light-delivery systems, because flexible silica-based fibers are no lnoger useable due to the high intrinsic absorption of silica. In additionl to light-transportation, only the HCW can be used as an intrinsic sensor: due to the long path-length through the HCW with similar intensity profiles at the input and output, the spectral absorption of the gas under test can easily be monitored. Up to now, the gases are analyzed in the MIR-region, mainly. However, the UV-region offers a lot of advantages. Using commercially available components for the UV-light source and the detector-system, the whole system with UV hollow-core-waveguides has to be studied in the wavelength-region from 170 nm up to 350 nm. With this experimental system, it is obvious to observe the UV-absorption of air and carbon dioxide below 200 nm, using nitrogen as a reference gas. In addition, ozone generated by the deuterium-lamp itself and several gas mixtures (e.g. 2 ppm toluene or xylene in cabon dioxide) were studied in detail.