The possible experts: how epistemic communities negotiate barriers to knowledge use in ecosystems services policy

notes: This paper is based on research carried out with the support of the European Research Council grant on Analysis of Learning in Regulatory Governance, ALREG http://centres.exeter.ac.uk/ceg/research/ALREG/index.php. The author wishes to thank the other authors in this special edition and in particular the issue editors Andy Jordan and Duncan Russel.publication-status: AcceptedClaire A Dunlop, 2014. The definitive, peer-reviewed and edited version of this article is published in Environment and Planning C: Government and Policy, 32(2), 2014.The increased saliency of how to value ecosystems services has driven up the demand for policy-relevant knowledge. It is clear that epistemic communities’ advice can show-up in policy outcomes, yet little systematic analysis exists prescribing how this can actually be achieved. This article draws on four decades of knowledge utilisation research to propose four types of ‘possible expert’ that might be influential on ecosystems services. The first section reports the broad findings of a literature review on knowledge use in public policy, and outlines the four-fold conceptualisation pioneered by Carol Weiss that defines the literature. Section two systematises the field by placing these four modes of knowledge use within an explanatory typology of policy learning. With how, when and why experts and their knowledge are likely to show-up in policy outcomes established, the article then proposes the boundaries of the possible in how the ecosystems services epistemic community might navigate the challenges associated with each learning mode. Four possible experts emerge. The expert with: political antenna and epistemic humility; the ability to speak locally and early to the hearts and minds of citizens; a willingness to advocate policy, and, finally, an enhanced institutional awareness and peripheral policy vision. The article concludes with a brief discussion of the utility of the analysis.European Research Counci

Dielectric microcavities for THz radiation: identical mode spectrum and coupling in poly-ethylene disks

We report the fabrication and characterization of identical dielectric whispering gallery microcavites for teraherz (THz) radiation. The THz radiation is coupled via a tapered waveguide into the coupled cavities. Mode splitting is observed. (C) 2008 Optical Society of Americ

Efficient III-V tunneling diodes with ErAs recombination centers

We report on recombination diodes containing monolayer depositions of ErAs between highly doped n- and p-layers in the (Al)GaAs and In(Al)GaAs material system. The ErAs material provides metallic states across the band gap of the host semiconductor that act as efficient recombination centers. Both electrons and holes can tunnel into the ErAs, resulting in extremely high tunneling current densities in the tens of kA cm(-2) range. A device resistance area product of 1-2 x 10(-5) Omega cm(2) at low bias (+/- 0.2 V) has been measured. Measurements on In(Al)GaAs and (Al)GaAs diodes will be compared to a simple theoretical model. Low band gap and high (p-) doping levels are identified as key parameters for achieving highest recombination currents. Compared to ErAs-free diodes, ErAs-enhanced recombination diodes provide orders of magnitude higher current densities at both moderate and low forward and reverse bias. This is attributed to the smaller and narrower tunnel barriers from the n- and p- layers into the ErAs compared to tunneling from the n- to the p-side through the whole depletion region

Telecom-Wavelength Compatible THz n-i-pn-i-p Super lattice Photomixers for Spectroscopical Applications

We report on the progress of room-temperature operating, continuous-wave, tunable n-i-pn-i-p superlattice THz photomixers, compatible with 1.55 mu m telecom laser systems. An output power of 0.2 mu W at 1 THz has been achieved at a photocurrent of 9.4 mA, using a broadband antenna. The spectral power is at a level where high resolution spectroscopy becomes attractive. This is demonstrated by measuring the absorption spectrum of water vapor between 0.4 and 1.6 THz

Arrayed free space continuous-wave terahertz photomixers

We present free space coherent arrays of continuous-wave terahertz (THz) photomixers and compare the results to on-chip arrays. By altering the relative phases of the exciting laser signals, the relative THz phase between the array elements can be tuned, allowing for beam steering. In addition, the constructive interference of the emission of N elements leads to an increase of the focal intensity by a factor of N-2 while reducing the beam width by similar to N-1, below the diffraction limit of a single source. Such array architectures strongly improve the THz power distribution for stand-off spectroscopy and imaging systems while providing a huge bandwidth at the same time. We demonstrate this by beam profiles generated by a 2 x 2 and a 4 x 1 array for a transmission distance of 4.2 m. Spectra between 70 GHz and 1.1 THz have been recorded with these arrays. (C) 2013 Optical Society of Americ

Coherent Superposition of Terahertz Beams from a Phased Linear Photomixer Array

We report on a 4 element linear array of free standing, tunable THz n-i-pn-i-p superlattice photomixers. The individual THz beams are coherently combined at a target plane distance of 4.2 m. The measurements of the interference pattern confirm the theoretically expected quadratic intensity increase of the center beam with the number of sources. At the same time, the beam waist is reduced in one dimension by a factor of 6 compared to a single beam. This technique allows for high resolution, THz stand off imaging

Continuous wave Terahertz emitter arrays for spectroscopy and imaging applications

We report on arrays of THz-emitters based on n-i-pn-i-p-superlattice photomixers for imaging and spectroscopic applications. The output power of a n-i-pn-i-p superlattice photomixers recently has reached nearly 1 mu W at 1 THz with a broadband antenna. There are no fundamental physical limitations at this stage for further improvement. Tunable continuous wave (CW) THz-sources for imaging and spectroscopy are highly desired tools for security and environmental applications. In particular, most stand-off imaging applications require a rather high THz power to allow for a sufficient dynamic range, and a narrow illumination spot size for high spatial resolution. Both goals can be reached by using an array of mutually coherent photomixers. We have simulated beam patterns for an arbitrary number of mutually coherent single sources with respect to a small beam size and high peak intensity. Here, we confirm the simulations experimentally by an array of 4 sources with a 4 inch THz optics. The beam profile is measured in the target plane at a stand-off distance of 4.2 m. As a result, the beam diameter is reduced by a factor of 6 and the peak intensity is enhanced by a factor of close to (4)(2) = 16, in excellent agreement with our simulations. Such an arrangement allows not only for high resolution stand-off imaging but also for spectroscopic investigations at stand-off distances. The THz frequency can be tuned over more than a decade (i.e. 0.1 to 2.5 THz) by tuning the wavelength of the mixing lasers. The spectral linewidth of the THz sources is only limited by the linewidths of the mixing lasers and can be made extremely narrow. A straightforward demonstration is achieved by water vapor spectroscopy in laboratory air with a single source