The inter-instrument, inter-laboratory, and long-term comparability of fluorescence data requires the correction of the measured emission and excitation spectra for the wavelength- and polarization-dependent spectral irradiance of the excitation channel at the sample position and the spectral responsivity of the emission channel employing procedures that guarantee traceability to the respective primary standards. In this respect the traceability chain of fluorometry is discussed from a radiometrist's point of view. This involves, in a first step, the realization of the spectral radiance scale, based on the blackbody radiator and electron storage ring, and the spectral responsivity scale, based on the cryogenic radiometer and their control via key comparisons of the national metrology institutes. In a second step, the characterization including state-of-the art uncertainties of the respective source and detector transfer standards such as tungsten strip lamps, integrating sphere radiators, and trap detectors used to disseminate these radiometric quantities to users of spectroscopic techniques is presented.

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Two-particle (exciton) states in equilibrium electron-hole plasmas of highly excited semiconductors are determined. In the framework of the Green's function technique, an effective (two-particle) wave equation allows to account for the influence of the surrounding plasma in terms of (dynamic) single-particle self-energies, Pauli blocking factors, and a dynamic effective potential correction. This equation is solved by expansion of the wave function in terms of Coulomb eigcnfimctions. No rational or pole approximation for the dielectric function is used. Exciton binding mcrgics and their imaginary parts (damping of the states) as well as continuum edges are given for Ge and GaAs model systems.Es werden Zwei-Teilchen-(Exzitonen-)Zustande in Elektron-Loch-Gleichgewichtsplasmen in hochangeregten Halbleitern bestimmt. Im Rahmen der Green-Funktionstechnik kann in einer effektiven (Zwei-Teilchen-) Wellengleichung der EinfluB des umgebenden Plasmas durch (tlynarnische) Ein-Teilchen-Selbstenergien, Phasenraumverbrauchsfaktoren und eine dynamische effektive Potcntialkorrektur beriicksichtigt werden. Diese Gleichung wird mittels Entwicklung der Wellenfunktion nach Coulomb-Eigenfunktionen gelost. Eine rationale oder Pol-Naherung fur die diclektrische Furiktion wird nicht verwendet . Exzitonen-Bindungsenergien und ihre Imaginarteile (Dampfung der Ziistande) sowie Kontinuumskanten werden fur ein Ge-und ein GaAs-Iblodellsystein angegeben.

Beam-limiting apertures with accurately known areas are required when measuring the radiance and irradiance of sources. We have already described a non-contact method for measuring aperture areas using a laser beam focused on the aperture surface. By shifting the aperture relative to the laser beam, and collecting and monitoring the reflected light, the onset of reflection was used to indicate the position of the aperture edges. We have now improved this approach by evaluating the position-dependence of the reflection signal recorded across the aperture edge. Whereas the former approach required a determination of the laser focus diameter to correct the measured aperture diameter, the quantity that makes the main contribution to the overall uncertainty of the aperture area, the new approach implicitly determines the laser focus diameter, so reducing the corresponding uncertainty and making it possible to determine aperture diameters with standard uncertainties of less than 0.2 µm. Measurements made in 1998 for aluminium apertures are compared with results obtained in 1995 using the same apertures.

The Method of Model Microfields proposed by Brissaud and Frisch is applied to calculate Stark broadened profiles of hydrogen lines in the static ion approximation. Numerical results for L-α, H-α, and H-β are found to be in good agreement with those derived from the unified theory by Vidal, Cooper, and Smith over a wide range of plasma densities and temperatures. This demon­ strates that reliable line profiles may be obtained from the microfield distribution and covariance alone, more complicated statistical features being less important in this context.

The influence of ion motion on Stark broadened hydrogen lines is studied using the Method of Model Microfields which allows a uniform unified treatment of electrons and ions. Contrary to former theoretical investigations, strong effects are found in the line centres of L-a, H-a, and H-ß which agree well with recent experimental findings, especially those of Wiese, Kelleher, and Helbig. E ffects o f I o n M o tio n o n H y d r o g e n S ta rk P ro files For the Stark broadening of hydrogen lines the unified theory developed by Voslamber 1 and Smith et al.2 provides a refined description of line profiles including the transition region from the "static" wing to the "impact" centre. Evaluating the results of the unified theory, Vidal, Cooper, and Smith3 (VCS) have compiled extensive tables of Stark pro files of low Lyman and Balmer lines which greatly facilitate the comparison to experimental results. A detailed experimental investigation of the Stark broadening of Balmer lines has been carried through by Wiese, Kelleher, and Paquette 4 (WKP) who give a short account as well of former measurements which have been done in the same range of plasma densities and temperatures (typical values are Ne = 1017 cm-3, T = 104 K ). As a general result, good agreement between theory and experiment is found in the line wings but the measured profiles exhibit much less structure in their central portions than those of VCS. A similar finding has been reported 5 for low electron densities, too, and the conclusion seems to be inevitable that not all the approxima tions used in the VCS calculations work as good in ithe line centre as has been estimated.Possible candidates are especially the neglect of time ordering in the evaluation of the effects of radiator-perturber collisions, and the assumption of a static ion microfield. The first of these is not a constituent part of the unified theory but may be removed at the expenditure of greater calculational efforts. Corresponding results of Roszman6 indicate that the inclusion of time ordering improves the agreement of experiment and theory, but certainly is not sufficient to remove the discrepancies. This has been made most obvious by a recent experiment Reprint requests to Dr. J. Seidel, Institut für Theoretische Physik der Universität Düsseldorf, Universitätsstraße 1, D-4000 Düsseldorf.of Grützmacher and Wende 7 who succeeded to mea sure the line centre of L-a for the first time. While they report a half width of more than twice the theoretical value, its increase by the consideration of time ordering in the VCS calculations 8 amounts to only 14%. This points out to an influence of ion dynamics much stronger than has been expected, and indeed there is convincing experimental support of this conjecture: Precision measurements of Wiese, Kelleher, and Helbig9 (WKH) revealed distinctly different line centres for various values of the ra diating atom-perturbing ion reduced mass /u. More over, these authors found that an extrapolation to jU = oc, based upon the assumption of a linear de pe...