TY - JOUR A1 - Ellis, S. C. A1 - Bland-Hawthorn, Joss A1 - Lawrence, J. A1 - Horton, A. J. A1 - Trinh, C. A1 - Leon-Saval, S. G. A1 - Shortridge, K. A1 - Bryant, J. A1 - Case, S. A1 - Colless, M. A1 - Couch, W. A1 - Freeman, K. A1 - Gers, L. A1 - Glazebrook, K. A1 - Haynes, R. A1 - Lee, S. A1 - Löhmannsröben, Hans-Gerd A1 - O'Byrne, J. A1 - Miziarski, S. A1 - Roth, M. A1 - Schmidt, B. A1 - Tinney, C. G. A1 - Zheng, J. T1 - Suppression of the near-infrared OH night-sky lines with fibre Bragg gratings - first results JF - Monthly notices of the Royal Astronomical Society N2 - The background noise between 1 and 1.8 ?mu m in ground-based instruments is dominated by atmospheric emission from hydroxyl molecules. We have built and commissioned a new instrument, the Gemini Near-infrared OH Suppression Integral Field Unit (IFU) System (GNOSIS), which suppresses 103 OH doublets between 1.47 and 1.7?mu m by a factor of 1000 with a resolving power of 10?000. We present the first results from the commissioning of GNOSIS using the IRIS2 spectrograph at the Anglo-Australian Telescope. We present measurements of sensitivity, background and throughput. The combined throughput of the GNOSIS fore-optics, grating unit and relay optics is 36?per cent, but this could be improved to 46?per cent with a more optimal design. We measure strong suppression of the OH lines, confirming that OH suppression with fibre Bragg gratings will be a powerful technology for low-resolution spectroscopy. The integrated OH suppressed background between 1.5 and 1.7 mu m is reduced by a factor of 9 compared to a control spectrum using the same system without suppression. The potential of low-resolution OH-suppressed spectroscopy is illustrated with example observations of Seyfert galaxies and a low-mass star. The GNOSIS background is dominated by detector dark current below 1.67 mu m and by thermal emission above 1.67 mu m. After subtracting these, we detect an unidentified residual interline component of 860 +/- 210 photons s-1 m-2?arcsec-2?mu m-1, comparable to previous measurements. This component is equally bright in the suppressed and control spectra. We have investigated the possible source of the interline component, but were unable to discriminate between a possible instrumental artefact and intrinsic atmospheric emission. Resolving the source of this emission is crucial for the design of fully optimized OH suppression spectrographs. The next-generation OH suppression spectrograph will be focused on resolving the source of the interline component, taking advantage of better optimization for a fibre Bragg grating feed incorporating refinements of design based on our findings from GNOSIS. We quantify the necessary improvements for an optimal OH suppressing fibre spectrograph design. KW - atmospheric effects KW - instrumentation: miscellaneous KW - infrared: general Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2966.2012.21602.x SN - 0035-8711 VL - 425 IS - 3 SP - 1682 EP - 1695 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Zakrevskyy, Y. A1 - Ritschel, T. A1 - Dosche, C. A1 - Löhmannsröben, Hans-Gerd T1 - Quantitative calibration - and reference-free wavelength modulation spectroscopy JF - Infrared physics & technology N2 - A unified model for quantitative description of harmonic spectra of gases obtained by wavelength modulation spectroscopy (WMS) technique is presented. In the model, both intensity modulation (IM) and frequency modulation (FM) of the laser emission are taken into account using minimum number of parameters. For the first time, the static behavior of a laser is described as a limiting case of its dynamic response. Laser and its driver are considered as a single device converting applied bias to laser emission. This allows application of the model to any type of laser and the introduced parameters can be assigned to the corresponding laser and/or driver properties. The approach was tested using a distributed feedback (DFB) laser spectrometer. Correctness of the proposed model is justified by very good agreement between the measured and modeled/fitted spectra, which allowed evaluation of the setup performance and assessment of modulation parameters of the DFB laser. An algorithm to minimize the time of numerical calculation of harmonic spectra using numerically approximated Voigt lineshape function was developed. Absolute values of the absorption line parameters (line strength and line width) were obtained from a single calibration- and reference-free spectrum scan with accuracy better than 0.1%. KW - Wavelength modulation gas spectroscopy KW - Diode laser KW - Isotope detection Y1 - 2012 U6 - https://doi.org/10.1016/j.infrared.2011.12.001 SN - 1350-4495 VL - 55 IS - 2-3 SP - 183 EP - 190 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Ast, Cindy A1 - Schmälzlin, Elmar A1 - Löhmannsröben, Hans-Gerd A1 - van Dongen, Joost T. T1 - Optical oxygen micro- and nanosensors for plant applications JF - Sensors N2 - Pioneered by Clark's microelectrode more than half a century ago, there has been substantial interest in developing new, miniaturized optical methods to detect molecular oxygen inside cells. While extensively used for animal tissue measurements, applications of intracellular optical oxygen biosensors are still scarce in plant science. A critical aspect is the strong autofluorescence of the green plant tissue that interferes with optical signals of commonly used oxygen probes. A recently developed dual-frequency phase modulation technique can overcome this limitation, offering new perspectives for plant research. This review gives an overview on the latest optical sensing techniques and methods based on phosphorescence quenching in diverse tissues and discusses the potential pitfalls for applications in plants. The most promising oxygen sensitive probes are reviewed plus different oxygen sensing structures ranging from micro-optodes to soluble nanoparticles. Moreover, the applicability of using heterologously expressed oxygen binding proteins and fluorescent proteins to determine changes in the cellular oxygen concentration are discussed as potential non-invasive cellular oxygen reporters. KW - oxygen sensor KW - biosensors KW - microsensors KW - nanosensors KW - endogenous sensor proteins KW - dual-frequency phase-modulation KW - phosphorescence quenching KW - plant science Y1 - 2012 U6 - https://doi.org/10.3390/s120607015 SN - 1424-8220 VL - 12 IS - 6 SP - 7015 EP - 7032 PB - MDPI CY - Basel ER -