TY  - JOUR
A1  - Boggio, Jose M. Chavez
A1  - Bodenmueller, D.
A1  - Fremberg, T.
A1  - Haynes, R.
A1  - Roth, Martin M.
A1  - Eisermann, R.
A1  - Lisker, M.
A1  - Zimmermann, L.
A1  - Boehm, Michael
T1  - Dispersion engineered silicon nitride waveguides by geometrical and refractive-index optimization
JF  - Journal of the Optical Society of America : B, Optical physics
N2  - Dispersion engineering in silicon nitride (SiXNY) waveguides is investigated through the optimization of the waveguide transversal dimensions and refractive indices in a multicladding arrangement. Ultraflat dispersion of -84.0 +/- 0.5 ps/nm/km between 1700 and 2440 nm and 1.5 +/- 3 ps/nm/km between 1670 and 2500 nm is numerically demonstrated. It is shown that typical refractive index fluctuations as well as dimension fluctuations during fabrication of the SiXNY waveguides are a limitation for obtaining ultraflat dispersion profiles. Single- and multicladding waveguides are fabricated and their dispersion profiles measured (over nearly 1000 nm) using a low-coherence frequency domain interferometric technique. By appropriate thickness optimization, the zero-dispersion wavelength is tuned over a large spectral range in single-and multicladding waveguides with small refractive index contrast (3%). A flat dispersion profile with +/- 3.2 ps/nm/km variation over 500 nm is obtained in a multicladding waveguide fabricated with a refractive index contrast of 37%. Finally, we generate a nearly three-octave supercontinuum in this dispersion flattened multicladding SiXNY waveguide. (C) 2014 Optical Society of America
Y1  - 2014
U6  - https://doi.org/10.1364/JOSAB.31.002846
SN  - 0740-3224
SN  - 1520-8540
VL  - 31
IS  - 11
SP  - 2846
EP  - 2857
PB  - Optical Society of America
CY  - Washington
ER  - 
TY  - GEN
A1  - Ellis, S. C.
A1  - Bauer, S.
A1  - Bacigalupo, C.
A1  - Bland-Hawthorn, J.
A1  - Bryant, J. J.
A1  - Case, S.
A1  - Content, R.
A1  - Fechner, T.
A1  - Giannone, D.
A1  - Haynes, R.
A1  - Hernandez, E.
A1  - Horton, A. J.
A1  - Klauser, U.
A1  - Lawrence, J. S.
A1  - Leon-Saval, S. G.
A1  - Lindley, E.
A1  - Löhmannsröben, Hans-Gerd
A1  - Min, S. -S.
A1  - Pai, N.
A1  - Roth, M.
A1  - Shortridge, K.
A1  - Waller, L.
A1  - Xavier, Pascal
A1  - Zhelem, Ross
T1  - PRAXIS: an OH suppression optimised near infrared spectrograph
T2  - Ground-based and Airborne Instrumentation for Astronomy VII
N2  - The problem of atmospheric emission from OH molecules is a long standing problem for near-infrared astronomy. PRAXIS is a unique spectrograph which is fed by fibres that remove the OH background and is optimised specifically to benefit from OH-Suppression. The OH suppression is achieved with fibre Bragg gratings, which were tested successfully on the GNOSIS instrument. PRAXIS uses the same fibre Bragg gratings as GNOSIS in its first implementation, and will exploit new, cheaper and more efficient, multicore fibre Bragg gratings in the second implementation. The OH lines are suppressed by a factor of similar to 1000, and the expected increase in the signal-to-noise in the interline regions compared to GNOSIS is a factor of similar to 9 with the GNOSIS gratings and a factor of similar to 17 with the new gratings. PRAXIS will enable the full exploitation of OH suppression for the first time, which was not achieved by GNOSIS (a retrofit to an existing instrument that was not OH-Suppression optimised) due to high thermal emission, low spectrograph transmission and detector noise. PRAXIS has extremely low thermal emission, through the cooling of all significantly emitting parts, including the fore-optics, the fibre Bragg gratings, a long length of fibre, and the fibre slit, and an optical design that minimises leaks of thermal emission from outside the spectrograph. PRAXIS has low detector noise through the use of a Hawaii-2RG detector, and a high throughput through a efficient VPH based spectrograph. PRAXIS will determine the absolute level of the interline continuum and enable observations of individual objects via an IFU. In this paper we give a status update and report on acceptance tests.
KW  - Near infrared
KW  - spectroscopy
KW  - OH suppression
KW  - astrophotonics
KW  - fibre Bragg gratings
Y1  - 2018
SN  - 978-1-5106-1958-6
U6  - https://doi.org/10.1117/12.2311898
SN  - 0277-786X
SN  - 1996-756X
VL  - 10702
PB  - SPIE-INT Soc Optical Engineering
CY  - Bellingham
ER  - 
TY  - JOUR
A1  - Schorck, Torben
A1  - Christlieb, Norbert
A1  - Cohen, Judy G.
A1  - Beers, Timothy C.
A1  - Shectman, Steve
A1  - Thompson, Ian
A1  - McWilliam, Andrew
A1  - Bessell, Michael S.
A1  - Norris, John E.
A1  - Meléndez, Jorge
A1  - Ramïrez, Solange
A1  - Haynes, D.
A1  - Cass, Paul
A1  - Hartley, Malcolm
A1  - Russell, Ken
A1  - Watson, Fred
A1  - Zickgraf, Franz-Josef
A1  - Behnke, Berit
A1  - Fechner, Cora
A1  - Fuhrmeister, Birgit
A1  - Barklem, Paul S.
A1  - Edvardsson, Bengt
A1  - Frebel, Anna
A1  - Wisotzki, Lutz
A1  - Reimers, Dieter
T1  - The stellar content of the Hamburg/ESO survey : V. the metallicity distribution function of the Galactic halo
N2  - We determine the metallicity distribution function (MDF) of the Galactic halo by means of a sample of 1638 metal-poor stars selected from the Hamburg/ESO objective-prism survey (HES). The sample was corrected for minor biases introduced by the strategy for spectroscopic follow-up observations of the metal-poor candidates, namely "best and brightest stars first". Comparison of the metallicities [Fe/H] of the stars determined from moderate-resolution (i.e., R similar to 2000) follow-up spectra with results derived from abundance analyses based on high-resolution spectra (i.e., R > 20 000) shows that the [Fe/H] estimates used for the determination of the halo MDF are accurate to within 0.3 dex, once highly C-rich stars are eliminated. We determined the selection function of the HES, which must be taken into account for a proper comparison between the HES MDF with MDFs of other stellar populations or those predicted by models of Galactic chemical evolution. The latter show a reasonable agreement with the overall shape of the HES MDF for [Fe/H] > -3.6, but only a model of Salvadori et al. (2007) with a critical metallicity for low-mass star formation of Z(cr) = 10(-3.4) Z(circle dot) reproduces the sharp drop at [Fe/H] similar to -3.6 present in the HES MDF. Although currently about ten stars at [Fe/H] < -3.6 are known, the evidence for the existence of a tail of the halo MDF extending to [Fe/H] similar to -5.5 is weak from the sample considered in this paper, because it only includes two stars [Fe/H] < -3.6. Therefore, a comparison with theoretical models has to await larger statistically complete and unbiased samples. A comparison of the MDF of Galactic globular clusters and of dSph satellites to the Galaxy shows qualitative agreement with the halo MDF, derived from the HES, once the selection function of the latter is included. However, statistical tests show that the differences between these are still highly significant.
Y1  - 2009
UR  - http://www.aanda.org/
U6  - https://doi.org/10.1051/0004-6361/200810925
SN  - 0004-6361
ER  - 
TY  - JOUR
A1  - Bland-Hawthorn, Joss
A1  - Ellis, S. C.
A1  - Leon-Saval, S. G.
A1  - Haynes, R.
A1  - Roth, Martin M.
A1  - Löhmannsröben, Hans-Gerd
A1  - Horton, A. J.
A1  - Cuby, J. -G.
A1  - Birks, T. A.
A1  - Lawrence, J. S.
A1  - Gillingham, P.
A1  - Ryder, S. D.
A1  - Trinh, C.
T1  - A complex multi-notch astronomical filter to suppress the bright infrared sky
JF  - Nature Communications
N2  - A long-standing and profound problem in astronomy is the difficulty in obtaining deep near-infrared observations due to the extreme brightness and variability of the night sky at these wavelengths. A solution to this problem is crucial if we are to obtain the deepest possible observations of the early Universe, as redshifted starlight from distant galaxies appears at these wavelengths. The atmospheric emission between 1,000 and 1,800 nm arises almost entirely from a forest of extremely bright, very narrow hydroxyl emission lines that varies on timescales of minutes. The astronomical community has long envisaged the prospect of selectively removing these lines, while retaining high throughput between them. Here we demonstrate such a filter for the first time, presenting results from the first on-sky tests. Its use on current 8 m telescopes and future 30 m telescopes will open up many new research avenues in the years to come.
Y1  - 2011
U6  - https://doi.org/10.1038/ncomms1584
SN  - 2041-1723
VL  - 2
IS  - 50
PB  - Nature Publ. Group
CY  - London
ER  -