3.9 THz spatial filter based on a back-to-back Si-lens system.

We present a terahertz spatial filter consisting of two back-to-back (B2B) mounted elliptical silicon lenses and an opening aperture defined on a thin gold layer between the lenses. The beam filtering efficiency of the B2B lens system is investigated by simulation and experiment. Using a unidirectional antenna coupled 3rd-order distributed feedback (DFB) quantum cascade laser (QCL) at 3.86 THz as the source, the B2B lens system shows 72% transmissivity experimentally with a fundamental Gaussian mode as the input, in reasonably good agreement with the simulated value of 80%. With a proper aperture size, the B2B lens system is capable of filtering the non-Gaussian beam from the QCL to a nearly fundamental Gaussian beam, where Gaussicity increases from 74% to 99%, and achieves a transmissivity larger than 30%. Thus, this approach is proven to be an effective beam shaping technique for QCLs, making them to be suitable local oscillators in the terahertz range with a Gaussian beam. Besides, the B2B lens system is applicable to a wide frequency range if the wavelength dependent part is properly scaled.

An angle-scanned cryogenic Fabry-Pérot interferometer for far-infrared astronomy.

The sensitivity of state-of-the-art superconducting far-infrared detectors used in conjunction with cryogenically cooled space telescopes and instrumentation is such that spectroscopic observations are generally limited by photon noise from the astronomical source or by galactic foreground or zodiacal emission within the field-of-view. Therefore, an instrument design that restricts the spectral bandpass viewed by the detector must be employed. One method of achieving background limited, high resolution spectroscopy is to combine a high resolution component such as a Fabry-Pérot interferometer (FPI) with a lower resolution, post-dispersing system, such as a grating spectrometer, the latter serving to restrict the spectral bandpass. The resonant wavelength of an FPI is most often tuned by changing the spacing or medium between the parallel reflecting plates of the etalon. In this paper, we present a novel design for an FPI in which the wavelength is tuned by scanning the angle of incidence on a high refractive index etalon. This concept simplifies the cryomechanical design, actuation, and metrology. The first results from the realized instrument are presented and compared with theory. The effects on the spectral response as a function of the incident angle have been simulated and shown to agree well with the observation.

Human biological monitoring for exposure assessment in response to an incident involving hazardous materials.

Biological monitoring in humans (HBM) is widely used in the field of occupational and environmental health. In the situation of an unexpected release of hazardous materials HBM may contribute to the medical support and treatment of exposed individuals from the general population or of emergency responders. Such exposure information may also be used to respond to individual concerns such as questions about a possible relationship between the chemicals released during the incident and health effects. In The Netherlands a guideline was prepared to support early decision-making about the possible use of HBM for exposure assessment during or as soon as possible following a chemical incident. The application of HBM in such an emergency setting is not much different from situations where HBM is normally used but there are some issues that need extra attention such as the choice of the biomarker, the biological media to be sampled, the time point at which biological samples should be collected, the ethics approval and technical implementation of the study protocol and the interpretation and communication of the study results. These issues addressed in the new guideline will support the use of HBM in the management of chemical disasters.

Effects of an extract of oystercatcher (Haematopus ostralegus) eggs from the Zeehavenkanaal in The Netherlands, and of its major contaminant, hexachlorobenzene, on the chicken embryo.

Oystercatchers (Haematopus ostralegus) foraging on the canal 'Zeehavenkanaal' in the Netherlands have been shown to accumulate appreciable amounts of contaminants, especially hexachlorobenzene. The present study was performed to assess the embryotoxic effects of the present contaminants. To this end, a two step approach was followed. In step one, the toxic effects of hexachlorobenzene were studied in the chicken embryo bioassay, using concentrations realistic for the field situation. In step two, yolks of oystercatcher eggs were extracted and the embryotoxic potency of this extract was studied in the same bioassay, using doses of 1, 10 and 100% of the contaminant load in one average egg. The extract contained hexachlorobenzene and PCBs. However, presence of other compounds could not be excluded, since these were not analysed. Hexachlorobenzene induced a nonsignificant decrease in lymphocyte density in the bursa of Fabricius. The egg extract caused a 3.5 fold induction of EROD activity at the highest dose applied, and decreased lymphocyte density in the bursa of Fabricius.