The Third Workshop in Teddington,
September 8 - 10, 1999
Abstracts of the Oral Presentations
Uncertainty and Confidence in Measurements
UKAS, Feltham, UK
All measurements are tainted by imperfectly known errors, so the significance associated with the result of a measurement must account for this uncertainty.
The objective of a measurement is to determine the value of the measurand, i.e. the specific quantity subject to measurement. A measurement begins with an appropriate specification of the measurand, the generic method of measurement and the specific detailed measurement procedure. No measurement is perfect and the imperfections give rise to error of measurement in the reported result. Consequently, the result of a measurement is only an approximation to the value of the measurand and is therefore only complete when accompanied by a statement of uncertainty.
The presentation will explore the reasoning behind, and the requirements for, the expression of a value of uncertainty associated with a measurement result. The principles will be illustrated by a typical example of uncertainty calculation for an ultraviolet measurement.
Measurement of Actinic Radiation
Lichttechnisches Institut, Universität Karlsruhe, Germany
In many UV applications, the direct quantitative acquisition of the actinic effect on the receiver of radiation is more adequate for monitoring and control of radiation processes than the measurement of the incident physical radiant quantity. In order to quantify photochemical, photobiological or photovoltaic effects, actinic radiant quantities Xact have to be introduced. If the additivity law is valid, they can be defined by means of the spectral radiant quantity Xel incident on the receiver and the relative spectral weighting function s(l )act,rel of the considered effect, i.e. the action spectrum as
Validity conditions and limitations of the van Krefeld law will be discussed as well as the applicability of the law of Bunsen and Roscoe which assumes the released effect to be dependent on the product of actinic irradiance and exposure time.
Nowadays, a lot of actinic effects of UV radiation are known and partially also their action spectra. These are not only the photobiological effects on the human skin and eye, as described in DIN 5031-10, but also effects on materials, such as
Action spectra of the UV will be presented and their spectral distribution will be interpreted as far as the respective photomechanisms and reactions are known. By an example, the procedure of measuring an action spectrum will be described and the uncertainties will be discussed.
Actinic radiometers are special broadband radiometers the relative spectral responsivity of which is matched to the action spectrum of the effect to be measured by means of appropriate optical filtering of the incident radiation. A proposal of the figure f1 which gives the relative deviation of measured Xact from the real value has been presented by the working group of the German FNL 7, together with WG 1 of the Thematic Network for Ultraviolet Measurements.
High Power UV-Lasers and UV Measurement Techniques for Excimer Lasers (157 nm – 351 nm) –
State of the Art and Future Developments
M. Rahe* and K. Mann†
* Lambda Physik GmbH, Göttingen, Germany
† Laser Laboratorium Göttingen e.V., Göttingen, Germany
In the last years the Excimer laser became a well-established tool for micro lithography and other industrial applications. Today Excimer lasers are the most powerful commercial UV laser sources and combine features like high peak power, short pulse length and high repetition rates in one laser source. Due to the UV wavelength they enable high-resolution processes and non-thermal micromachining.
Examples for industrial applications are the parallel drilling of ink jet nozzle arrays, recrystallisation of amorphous Si for TFT flat panel displays or DUV microlithography for manufacturing of high-integrated microchips.
All these applications have special customised requests on the laser sources. At present a tendency to higher energies, higher energy stability and shorter wavelength is observable.
The use of F2 Excimer laser sources, emitting at 157 nm, is becoming a new promising tool. The 157-nm radiation will enable fundamental research and development for Deep UV (DUV) high-resolution optical microlithography in the manufacturing of integrated circuits. Furthermore benefits are expected for the micromachining of tough materials for micro optics fabrication.
Lambda Physik has developed special laser sources optimised for the various applications with the aim to fulfil all the demands.
In order to take full advantage of these benefits of high power UV lasers in the industrial production, efforts with respect to over-all system reliability and long term stability have to be undertaken. For example, especially at the wavelengths 193 nm and 157 nm the employed optical components still suffer from substantial losses due to both absorption and scattering. Moreover, ageing phenomena like laser–induced colour centre formation or compaction in fused silica are limiting factors.
In order to improve the efficiency of beam steering systems, the performance of DUV optics is characterised at Laser-Laboratorium Göttingen by measuring absorption and scatter losses during Excimer laser irradiation. Absolute absorptance is determined by high-resolution laser calorimetry, which can also be employed for fast monitoring of colour centre formation. Total scatter losses in DUV optics are obtained using a Coblentz hemisphere as integrating element. Results of quantitative absorption and scatter measurements on state-of-the-art optics for 193 nm are presented.
An overview of the current status of Excimer laser development and beam characterisation is given, putting main emphasis on the evaluation of industrial relevant parameters like pointing stability, pulse-to-pulse fluctuations or plateau uniformity and edge steepness of the beam profile.
UV-Measurements in Artificial Weathering of
Swedish National Testing and Research Institute, Borås, Sweden
To simulate environmental stress affecting outdoor durability of polymeric materials so called artificial weathering tests are used. Based on the results of such tests the long-term performance or the service life of the materials tested can be predicted prior to use. The environmental degradation factors taken into account in artificial weathering tests, however, have to be limited and are most often restricted to solar radiation, black standard temperature, humidity and moisture. As photochemical degradation is one of the most important factors for the outdoor durability of polymeric materials, the choice of light source and filters is critical in respect of correct spectral power distribution of photo activating UV light.
Although different kinds of light sources are used in artificial weathering, like for example fluorescent UV lamps, xenon arc lamps, and carbon arc burners, it is the xenon arc lamp, fitted with borosilicate filters, that gives the best simulation of the sunlight. The use of this lamp/filter combination in artificial weathering improves the correlation between laboratory and outdoor test results, but to gain reproducible laboratory test results, accurate control of UV light intensity and spectral power distribution are required.
Most devices for artificial weathering offer irradiance control systems that attempt to maintain a correct spectral power distribution, either by narrow-band control of UV light intensity at e.g. 340 nm, or by broad-band control of intensity in the region 300 - 400 nm. Problems, however, requiring special attention to UV measurements do exist and are associated with:
Large efforts have been made and are being paid to increase the reproducibility of artificial weathering tests. In that respect UV measurements and control of UV light intensity and spectral power distribution constitute one of the most crucial factors.
Integral UV-Meters - Physical principles - States of the art - Problems of Applications
Anton Gugg-Helminger and Tran Quoc Khanh
Gigahertz Optik GmbH, Puchheim-Munich, Germany
An integral radiometer head is an optical system, whose relative spectral responsivity is matched to an actinic function responsible for a certain photobiological / chemical effect. Generally, an integral UV-meter consists of input optics, an optical filtering system, a detection unit converting the incoming radiation into an evaluable signal, and an information medium indicating the functional relation between the radiation and the output signal.
There are various ways to implement the parts of the integral radiometers. The input optics for irradiance measurements may consist of an integrating sphere, a diffuse reflector, diffusely transmitting material, or a fibre bundle sphere arrangement. Input optics for radiance measurements may also contain mirrors or lenses. The filtering systems may contain optical filters, biofilms, Polysulphone film badges, and luminescent materials. As detectors, PMT’s, photo cells, semiconductor detectors, or biological-chemical detectors can be used.
This presentation will give an overview on the physical principles of the integral UV-meters. Also, state-of-the-art of the integral UV-meters will be discussed. The various problems associated with UV-materials set the limits to what may be obtained. Some drafts on the state-of-the-art have been made within the Working Group 1 of this UV-network. Various problems with integral UV-meters will be issued. The problems on the user side are the problems to be overcome by the manufacturers of the measuring equipment. In addition, the meter developing engineers have their own additional problems on the manufacturing side.
Many users of UV-meters are not able to correctly determine and evaluate their measurement results. The UV topic is, and retains, a difficult topic for the practical industrial measurements. A correct and relevant choice of a UV-meter for a practical measuring task is a big problem to overcome. There is no guideline for specifying the UV-meters. This necessitates intensive courses and training by experts, who should be not only from standard institutes or universities, but also from industrial laboratories. This UV-Network could contribute to these activities. Within a couple of months, a recommendation will be published in Germany , which will show with practical steps and algorithms, how to measure and evaluate the UV-radiation hazards on the UV work places and how to choose the suitable spectral and / or integral UV-meter for these measuring tasks.
 P. Knuschke, T. Q. Khanh, M. Brose, and H.-U. Heidrich, "Risikoanalyse für Arbeitsplätze mit Expositionen durch künstliche UV-Strahlenquellen," Strahlenschutzpraxis, September 1999, in press.
Abstracts of the Poster Presentations
Measurements of Intense UV-Radiation in the Coating, Lacquer and Semiconductor Industry
Tran Quoc Khanh, Wolfgang Dähn, and Anton Gugg-Helminger
Gigahertz Optik GmbH, Puchheim-Munich, Germany
Intense mercury high- or medium-pressure lamps are used world-wide in the photolithography, in the semiconductor industry, and in the UV-equipment for curing lacquers and coatings. The cure processes are based on the polymerisation reactions, in which by absorption of UV-radiation in the photoinitiators, the radicals can be free enabling the monomers being reactive to polymers. Polymerisation effective radiation spreads between 180 nm and around 470 nm.
In order to accelerate the cure processes, very high effective UV-irradiances on the material surface up to 100.000 W m-2 should be applied. The distance between lamp arrangements and material is approximately 20 mm - 60 mm causing an operating temperature of around 200°C or more. In the photolithography, the temperature can be between 80°C and 100°C. Highly stable and spectrally flat radiometer heads are necessary for these applications.
Up to now, there were only a small number of radiometer manufacturers in this field. The radiometers available consist of radiation collecting optics, a filter set and a semiconductor detector built-in in a metal housing. Under intense irradiation directly on the housing, the ageing of all optical components is enormous making a further accurate measurement impossible after a short measuring time.
In the recent time, Gigahertz-Optik GmbH (Puchheim, Germany) started successfully the developments and fabrications of new type and high stable UV-radiometers. These radiometers consist of the following systems:
Experiments with high-power reflector incandescent lamps causing a temperature of 170°C on the integrator surface showed a signal change of less than 2 % over 2 hours. With a mercury high-pressure lamp with 5-kW lamp power and with an effective UV-irradiance of about 14.000 W m-2 at 90°C a signal change of maximal 2-3 % was determined over around 6 hours. No irreversible effects can be indicated. The housing of the radiometer head is 8 mm high.
Radiometer heads built in this way were fabricated for the polymerisation effective (actinic) spectra depicted in Figure 1.
Figure 1. Action spectra for some radiometers realised.
Indication of Dangerous Levels of Ultraviolet Radiation of the Sun with Coloured Crystals
S. I. Anevskiy*, A. V Demin†, and A. F. Zerrouk‡
* Russian Research Institute of Optical & Physical
Measurements of State Standard of Russia
† Central Research Institute of Study of Materials,
JSC "Komposit," Moscow, Russia
‡ UTAR International Ltd., British Columbia, Canada.
This work describes the creation of additively coloured halogen-alkaline crystals that change colour from colourless to pale blue when ultraviolet radiation (UVR) of the natural Sun reaches a level hazardous to human health. These UVR levels were established by the US National Institute On Safety and Health in 1975 (NIOSH, 1975) and are defined as a Threshold Limit Values (TLV) curve.
It is shown that the maximum absorption peak of the same crystal type during the additive colouring could be changed within the wavelength range 288 - 295 nm and with a fairly good solution. For example, a crystal with the wavelength of the maximum absorption at l = 295 nm has D l = 10 nm (full width at half maximum). This practically solves the equation
and allows us to define the operating point on the TLV curve. In Eq. (1), i is the spectral irradiance in the waves’ interval D l , E(l ) is the spectral irradiance, S(l ) is the relative spectral effectiveness, and D l is the bandwidth. Under the conditions of relatively continuous spectrum of natural sun in the wavelength range 280 - 315 nm, it is quite sufficient for the absolute conjunction with the sun’s irradiance and for the definition of the hazardous level of UVR.
This work shows that the sensitivities of the obtained crystals are at the maximum levels in the beginning of the exposure with UVR. Later they get lower, at the same time forming (under 300°K) a stable complex band of absorption in the range of l ~ 690 nm, which turns the crystal pale blue in colour. This band is formed because of the transformation of the crystals’ photosensitive centres to the electronic centres of colour under the influence of narrow-band UVR.
The work also shows the kinetics of the formation and destruction of crystal’s coloration centres. The threshold energy value for the formation of long-wave complex absorption band (l ~ 690 nm) within the timeframe of 1 to 10 minutes was selected by taking into consideration the relative spectral effectiveness S(l ). The selected timeframe corresponds to 30 dm / m2 with simultaneous irradiation of visible light with intensity of 600 - 1.599 V / m2. This enables us to determine the attainment of TLV in different latitudes, i.e. to determine the threshold of hazardous level of UVR of natural Sun and to take the necessary protection measures.
It is shown that the crystal could also be used for the indication of minimal erythemal dose (MED) for skin types classification. For this purpose, besides the adjustment of the absorptive maximum to the MED curve, a special technology of coating the crystals with various polymers was developed, which allows us to match the crystal’s sensitivity to different types of skin. Therefore, usage of a coloured crystal allows us to determine, with the help of either the TLV curve or MED, a precise moment and time after which exposure to UVR will become hazardous.
Measurements of Spectral UV-Reflectance of
Arctic Snow and Ice
J. B. Ørbæk*, Boris Ivanov†, and Stefan Claes*
* Norwegian Polar Institute, Tromsø, Norway
† Arctic and Antarctic Research Institute, St. Petersburg, Russia
The surface radiation depends not only on the optical properties of the atmosphere and the solar zenith angle, but to a significant amount also on the reflectance properties of the surface (albedo). High albedo surfaces in the Arctic increase the apparent atmospheric transmittance due to a significant multiple scattering of solar radiation between the surface and the atmosphere or clouds, most significantly at ultraviolet and visible wavelengths. The spectral reflectance of snow and ice varies significantly during the transition period from winter to summer, as the snow-pack gradually changes its character from dry conditions with small snow crystals to wet snow with large crystals during melt, and eventually to snow free conditions.
Observations of the spectral reflectance of arctic snow and ice at ultraviolet wavelengths has been performed by means of standard radiance measurements of snow covered surfaces at different stages of melting. The reflectance measurements were done with a portable spectrometer of type FieldSpec covering the spectral region UVA, VIS and NIR, and with a semi-portable Bentham DM150 UV-spectrometer in the spectral region UVB and UVA. Simultaneous determination of water content, impurities and grain size etc. of the snow and ice has also been performed. The determination of the spectral ultraviolet albedo by the method used in this study depends to a less extent on the exact calibration of the optical systems, but to a large extent on special considerations and careful calibration of the white reference Spectralon used in the measurements.
Biologically Weighted Measurement of UV Radiation in Space and on Earth with the Biofilm Technique
P. Rettberg and G. Horneck
DLR, Institute of Aerospace Medicine, Köln, Germany
Biological dosimetry has provided experimental proof of the high sensitivity of the biologically effective UVB doses to changes in atmospheric ozone and has thereby confirmed the predictions from model calculations. The biological UV dosimeter ‘biofilm’ whose sensitivity is based on dried spores of B. subtilis as UV target weights the incident UV radiation according to its DNA damaging potential. Biofilm dosimetry was applied in space experiments as well as in use in remote areas on Earth. In space biofilms were used to determine the biological efficiency of the extraterrestrial solar UV, to simulate the effects of decreasing ozone concentrations and to determine the interaction of UVB and vitamin D production of cosmonauts in the MIR station. Examples are long-term UV measurements in Antarctica, measurements of diurnal UV profiles parallel in time at different locations in Europe, continuous UV measurements in the frame of the German UV measurement network and personal UV dosimetry.
On the Uncertainty of the UV Irradiance Scales
Finnish Meteorological Institute, Helsinki, Finland
The primary irradiance standard of a calibration site is a basis on how comparable one’s spectral UV measurements are with those of the others. The uncertainty related to this standard was investigated by purchasing the calibration of 1.000-W DXW lamps from the following five laboratories offering such a service: Finnish Radiation Protection Authority, Gigahertz-Optik GmbH, Swedish Testing and Research Institute, Optronic Laboratories Inc., and Helsinki University of Technology. For most of them the experiment was repeated twice. The laboratories provided the calibration according to their normal procedure applied to any customer. For most of them the experiment was repeated twice.
The irradiance scales given by the lamps and their certificates were compared at the laboratory of Jokioinen Observatory, Finland, by measuring the spectral irradiance of each lamp three times successively using a double monochromator Brewer Mk-III #107. The optical axis was vertical which was also required by the calibration laboratories. The measuring distance was 500 mm. The stability of the instrument was monitored during the entire experiment by using a portable 50-W UVB Lamp Kit, and by measuring the output of an internal standard lamp at fixed wavelengths in UVB and UVA. The wavelength setting of the instrument was checked before each measurement by using the 296,9-nm emission line of an internal mercury lamp. The measurements were performed in a dark room equipped with calibrated electronics and a thermal stabilisation to within ± 0,5ºC.
The stability of each lamp was monitored by recording the voltage drop over the lamp, and by measuring its radiant power with two temperature-controlled broadband silicon detectors, one being sensitive in UVB and the other in UVA. All control and environmental information was recorded at a time interval of 2 to 3 seconds.
The preliminary results indicate larger differences than expected. At first some individual calibrations suffered from human errors in the data which could only be detected by having other calibrations as a reference. These were, of course, corrected by the originator before continuing the analysis. At the end the irradiance scales could differ by up to 10 % through the whole wavelength range, even in the case of a common physical laboratory as the origin of the traces.
The observed differences may not offer a statistically significant sample for the estimation of the uncertainty of the primary standard of one’s home laboratory. However, they serve as an example on the possible differences in the scales of data sets based on irradiance traces obtained from different laboratories. Consequently, in instrument intercomparison campaigns the trace of each instrument’s calibration should be taken into account in more detail: If the majority uses one calibration laboratory, they are more likely to dominate in the determination of a campaign reference although it is hard to say whether they are "all right or all wrong". The home data sets of each instrument would probably also benefit from having a calibration obtained from more than one laboratory.
The Responsivity of UV Meters used in Broadband, Extended Sources: A Comparison of Two Different Approaches.
A. J. Coleman
Medical Physics Directorate, Guy’s & St. Thomas’ NHS Trust, London, UK
The effective responsivity of two UV meters (a Waldmann GmbH 585.100 and International Light Inc. IL1700A), commonly used to measure irradiance in the broadband, extended sources employed in phototherapy, have been determined using two different approaches. The first approach involves the comparison of the meter response with the measured irradiance obtained using a calibrated double-grating spectroradiometer in a simulated phototherapy source consisting of an array of fluorescent tubes. Traceability to national standards is via a reference tungsten lamp used to calibrate the spectroradiometer.
In the second method, the effective responsivity is determined by calculation from the measured spectral and spatial responsivity of the meter along with reference data on the spectral and angular distribution of radiance obtained from a sample phototherapy source of the required type. The spectral responsivity of the meter is determined by intercomparison with that of a reference meter in a normally incident monochromatic light field. These measurements can be made with an expanded uncertainty of 7 % (k = 2). Spectral and angular correction factors are then calculated for the given source type and used to derive the effective responsivity of the meter.
Reasonable agreement is noted between the effective responsivities of both meters obtained by the two methods. The second method has the advantage of obviating the requirement for calibration centres to maintain a range of spectrally and geometrically similar extended, broadband light sources without loss of accuracy. It also removes the variability associated with ageing of fluorescent tubes and repeat, in-house, calibrations of the spectroradiometer. It has the additional advantage of a shorter traceability chain, with traceability being provided by via relatively cheap, accurate, stable and linear silicon photodiode based reference meters rather than the more expensive reference lamps which require more complex handling. These factors significantly improve the reproducibility of the calibration.
Measurements of Erythemal Doses and Spectral Characterisations of Various UV Radiation Sources Using the Biochip Viospor - the New UV-Detection Film System
H. Holtschmidt and L. Quintern
BioSense, Laboratory for Biosensory Systems, Bornheim, Germany
A. The problem: It is very difficult to measure the UV-dose, especially under field conditions. Spectroradiometers are required to obtain exact and highly reproducible measurement results - a procedure that entails the cost-intensive and personal-intensive use of manpower. For underwater measurements in the sea also only spectroradiometric measurements were used. It was not possible to monitor the erythemal weighted UV-exposure conditions for UVA and UVB spectral region at the workplace with a film dosimeter similar to those that are used to detect X-rays and radioactive radiation. There was no easy-to-use, cheap and compact UV-dosimetry system on the market which could be used for all these UV measurements and which would guarantee highly precise measurement results. The spectral response of those detectors to measure erythemal effective doses has to match the CIE action spectrum for erythema not only in the UVB but also in the UVA. This is especially important for low solar elevation angles, for solar radiation filtered by window glass, and for artificial radiation sources such as solaria which may have a high UVA emission intensity.
B. The innovation: Here we present the new UV detection film VioSpor (spore film). The spectral response of this film is optimised to measure erythemally-weighted irradiance in different radiation environments. Thus, it can be used as well for solar radiation measurements and measurements of artificial lamps, like solaria. Additionally to the dose determination the spectra can be characterised by a differential measuring technique using simultaneously a set of different filters in a single spore film biochip.
C. The technique: The method is based on three main components: 1. A biological UV-sensitive photo film; 2. A special filter-optic system; 3. The protective dosimeter casing. To 1. The basis of the biological film are highly sensitive DNA molecules of immobilised spores which produce a responsivity profile which corresponds to that of human skin for the triggering of sunburn (in accordance with IRPA, EN 60 335-5-27 and DIN 5050/CIE). To 2. The filter-optic system imitates the UV-filtering effect of the outermost layers of the skin functions. To 3. The biological film and the filtering system were included in the protective dosimeter casing. Its compact construction guarantees protection against most difficult environmental influences and a very high degree of user friendliness.
D. The results: To test the capacity of the VioSpor UV-dosimetry system different laboratory tests (Quintern et. al. 1992, 1997) and tests in the field were done (Holtschmidt et. al. 1998, Furusawa et. al. 1998). The VioSpor-system was tested in field campaigns to compare the data with spectroradiometric measurements. This was done in mid and low latitudes at various solar elevation angles. Values of the daily erythemal dose which were derived from spectroradiometer measurements performed in Germany (Garmisch) and in Japan (Sapporo and Naha) well agree with the VioSpor data. The VioSpor data also fit quite well to the spectroradiometric measurements for low solar elevations when the UVA part of the solar spectrum is relatively enhanced compared to the UVB. Under good weather conditions, the intercomparison results indicate that this spore film dosimeter agrees with the CIE-weighted spectral measurements to within ± 10 %. This standard deviation is similar to the standard deviation that could be achieved during the last German spectroradiometer intercomparison in 1997 (Seckmeyer et. al. 1997).
E. Conclusion: The benefits of the new dosimeter can be summarised as follows: I. It could be demonstrated that this biotechnological dosimetry method could be used to determine erythemal doses for a variety of different radiation environments. II. It is the first broadband film radiometer optimised for UVB and for UVA. III. It is easy to use for everyone everywhere. The compact very robust construction of the casing (weight: 10 to 30 g, dimensions height: 1,2cm, Ø: 3,2cm) and its water resistance makes it suitable for personal dosimetry in leisure time and at work place, in solaria, for meteorology, scientific research etc. IV. Additionally to the dose determination the spectra of a given UV source can be characterised by a differential measuring technique giving the wavelength at which 50 % of the total erythemal effective dose is caused by longer and shorter wavelengths respectively.
 L. E. Quintern, G. Horneck, U. Eschweiler, and H. Bücker, "A biofilm used as ultraviolet-dosimeter," Photochem. Photobiol. 55, 389-395 (1992).
 L. E. Quintern, Y. Furusawa, K. Fukutsu, and H. Holtschmidt, "Characterization and application of UV detector spore-films: the responsivity curve of a new detector system provides good similarity to the action spectrum for UV-induced erythema in human skin," J. Photochem. Photobiol. B: Biol. 37, 158-166 (1997).
 H. Holtschmidt, Y. Furusawa, M. Saito, and G. Seckmeyer, "MED measurements and spectral characterisations of various UV radiation sources using the biochip VioSpor® - a new UV-detection film system," in Abstracts of the ECUV Congress, Helsinki 1998.
 Y. Furusawa, L. E. Quintern, H. Holtschmidt, P. Koepke, and M. Saito, "Determination of erythema effective solar radiation in Japan and Germany with a spore monolayer film optimized for the detection of UVB and UVA - results of a field campaign," Appl. Microbiol. Biotechnol. 50, 597 - 603 (1998).
UVB and Ozone Distributions between Cape Town and Bremerhaven from 27.05.98 to 21.06.98
Saad El Naggar*, Otto Schrems*, Thaddaeus Bluszcz*, and T. Hanken†
* Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany
† ISITEC GmbH, Bremerhaven, Germany
We have performed UVB and ozone measurements during the ANT XV/5 cruise f the German RV "Polarstern" between Cape Town (South Africa, 38° S) and Bremerhaven (Germany, 54° N) from 27.05.98 to 21.06.98. The main objectives of this campaign were:
The following instruments were used:
The results show big meridional variations of ozone and UVB distributions. Ozone concentrations were between 250 and 360 DU and UVB erythemally weighted daily doses were between 6 and 18 MED (1.500 - 4.500 W s / m2). The unweighted UVB-daily doses were between 25.000 and 110.000 W s / m2. The maximum erythemally weighted UVB irradiance was about 265 mW / m2. The factor between ELUV-14 measured doses and the erythemally-weighted doses was about 1,65. Considerable deviations between the instruments were found (more than ± 10%).
All results will be presented.
Simulation of Solar UV Radiation at Ground for Biological Effects on the Marine Ecosystem
H. Tüg*, Ch. Groß*, and T. Hanken†
* Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany
† ISITEC GmbH, Bremerhaven, Germany
Penetration of the harmful UV irradiation in the earth’s atmosphere is mainly inhibited by the ozone layer. At wavelengths below 315 nm (UVB: 280 - 315 nm) absorption of the ozone increases so steep, that one speaks about an edge in the spectrum. Due to the fact, that for millions of years the share of the UVB in the sun’s irradiation on ground is only about 1 %, organisms are not adapted to higher values in the UVB range by evolution. The ozone depletion observed in the last decades, leads inevitably to a shift in the cut-off edge of the spectrum. Therefore certain effort is undertaken to estimate the possible damages of flora, fauna, and man.
Research in field is restricted by changing atmospheric conditions like sun elevation, clouds, aerosol etc. For research on the marine ecosystem additionally the water column with changing optical properties plays an important role. Therefore we developed an instrument to simulate the sun’s irradiation at ground including variable impact from clouds, aerosol, ozone, water column etc. in the laboratory.
As light source we use a 400-W metallogen lamp, the spectrum of which is adapted to the solar spectrum by adding some rare earth elements. The light of this lamp first passes a wavelengths independent absorber to simulate clouds. Behind it passes 3 liquid filters and a diffuser. These filters are of variable thickness and the contain solutions of copper sulphate, potassium nitrate, and potassium chromate. Due to the different absorption characteristics it is possible to simulate most natural irradiation situations by combination of varying concentrations of the solutions and thickness of the filter layers. Especially the copper sulphate is very suitable to simulate the cut-off edge of the solar spectrum by ozone absorption. For calibration, the simulators irradiance is measured with a spectroradiometer and compared with the sun’s spectrum at well known atmospheric conditions.
With this instrument it is possible to make experiments under stable conditions for any period of time necessary and to change all parameters independently like ozone, clouds, aerosol or depth in water. The solar radiation simulator is used for research on phytoplankton, macroalgae and fish eggs at the moment.
Interpretation of UV-Effects on the Internal Quantum Efficiency of Silicon Photodetectors
T. Kübarsepp, P. Kärhä, and E. Ikonen
Metrology Research Institute, Helsinki University of Technology, Finland
The internal quantum efficiency (IQE) of a photodetector is defined as the average number of recorded electron-hole pairs created per one absorbed photon. It has to be accurately known in order to interpolate the spectral responsivity of semiconductor photodetector with a high level of accuracy. The internal quantum efficiency of silicon photodetector is close to unity throughout the visible and in the near infrared regions. In the near ultraviolet region, IQE increases as the quantum yield of silicon increases. In addition, the temporal change in IQE has been measured as the functions of irradiation wavelength and time of exposure at low doses.
We have developed a semi-empirical interpolation function to describe the effects of the quantum yield of silicon and time of exposure on IQE in the near UV. The physical basis for the modelling of the quantum yield utilises an assumption about the direct transitions at the k = 0 point in the first Brillouin Zone after the absorption of a photon with energy higher than the direct band-gap of silicon. The effect of continuous ultraviolet irradiation on the responsivity is interpolated by using 1-dimensional model of a photodiode in which most of the UV-light is absorbed near the SiO2 / Si interface. In this region of silicon photodetector, the collection efficiency is modelled as a function of concentration of defects near the interface.
We present the results of comparison between the measured and the modelled spectral responsivities of silicon photodetectors. The relative spectral responsivity of a silicon trap detector in UV was measured by using a pyroelectric radiometer. From the measured spectral responsivity data, the quantum yield of silicon was derived, the values of which were interpolated by using the developed model. The comparison between the measured and the modelled quantum yield values shows a good agreement, ± 0,7 %, within the wavelength region from 250 nm to 400 nm.
By using the developed interpolation methods, the measured change in the spectral responsivity of silicon photodiodes due to UV radiation can be completely accounted for by adjusting the collection efficiency near the SiO2 / Si interface. The physical reason for the time-dependent change in the value of the collection efficiency is the decreasing recombination rate due to wavelength selective bleaching of the defects near the SiO2 / Si interface.
The developed interpolation function for the internal quantum efficiency can be used to extend the predictability of the spectral responsivity of silicon photodetectors into the wavelength region from 250 nm to 950 nm, offering improvements in several applications in the field of high-accuracy radiometry.
Rare earth doped Sol-gel Materials as
Potential Absorbance Standards
Séverine Aubonnet and Carole C. Perry
The Nottingham Trent University, Department of
Chemistry and Physics, United Kingdom
Our studies are aimed towards the preparation of absorbance materials for use in the UV region. Sol-gel silica monoliths have been chosen as the vehicle for the preparation of such standards as it is possible to prepare materials at low temperature without the need for sophisticated equipment and at minimal cost. In this contribution we discuss the preparation of porous and non-porous glasses with cerium(III) (as a potential UV standard) and a combination of cerium(III) and neodymium(III) (as a potential combined UV and visible standard). Our current research is directed towards understanding the extent of molecular interactions between the dopant phase (in this case metal salts) and the gel matrix and the effect of these interactions on the spectroscopic signature of all components in the gel-glass composite.
Materials have been prepared using the pre-doping method. The dopant was either CeCl3.7H2O prepared in ethanol or CeCl3.7H2O and Nd(NO3)3.6H2O prepared in ethanol with initial solution concentrations between 1 M and 10-7 M although the lowest concentration at which the spectroscopic behaviour of the metal ion is observed is 10-3 M.
The presence of the cerium(III) metal ion affects the rate of drying of the gel-silicas as we have found in a previous study using neodymium(III) ions alone  suggesting a direct interaction between the gel matrix and the metal ions themselves. Confirmatory evidence has been provided by low temperature 29Si solution NMR measurements during the early stages of gel formation. The solution UV-VIS spectrum of CeCl3.7H2O is detected when the metal ion is present in the sol-gel but when cerium(III) and neodymium(III) are added together the signal arising from the presence of the cerium ions is diminished. Moreover after evacuation of the glasses and heat treatment (800°C), the presence of neodymium(III) can only be observed suggesting a transformation of cerium(III) to cerium(IV) which does not have any apparent peaks in the UV-VIS region of the electromagnetic spectrum.
 C. C. Perry and S. Aubonnet, J. Sol Gel. Science and Technol. 13, 593 (1998).