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  - JOUR
A1  - Salffner, Katharina
A1  - Boehm, Michael
A1  - Reich, Oliver
A1  - Löhmannsröben, Hans-Gerd
T1  - A broadband cavity ring-down spectrometer based on an incoherent near infrared light source
JF  - Applied physics : B, Lasers and optics
Y1  - 2014
U6  - https://doi.org/10.1007/s00340-014-5762-9
SN  - 0946-2171
SN  - 1432-0649
VL  - 116
IS  - 4
SP  - 785
EP  - 792
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Schirmack, Janosch
A1  - Boehm, Michael
A1  - Brauer, Chris
A1  - Löhmannsröben, Hans-Gerd
A1  - de Vera, Jean-Pierre Paul
A1  - Moehlmann, Diedrich
A1  - Wagner, Dirk
T1  - Laser spectroscopic real time measurements of methanogenic activity under simulated Martian subsurface analog conditions
JF  - Planetary and space science
N2  - On Earth, chemolithoautothrophic and anaerobic microorganisms such as methanogenic archaea are regarded as model organisms for possible subsurface life on Mars. For this reason, the methanogenic strain Methanosarcina soligelidi (formerly called Methanosarcina spec. SMA-21), isolated from permafrost-affected soil in northeast Siberia, has been tested under Martian thermo-physical conditions. In previous studies under simulated Martian conditions, high survival rates of these microorganisms were observed. In our study we present a method to measure methane production as a first attempt to study metabolic activity of methanogenic archaea during simulated conditions approaching conditions of Mars-like environments. To determine methanogenic activity, a measurement technique which is capable to measure the produced methane concentration with high precision and with high temporal resolution is needed. Although there are several methods to detect methane, only a few fulfill all the needed requirements to work within simulated extraterrestrial environments. We have chosen laser spectroscopy, which is a non-destructive technique that measures the methane concentration without sample taking and also can be run continuously. In our simulation, we detected methane production at temperatures down to -5 degrees C, which would be found on Mars either temporarily in the shallow subsurface or continually in the deep subsurface. The pressure of 50 kPa which we used in our experiments, corresponds to the expected pressure in the Martian near subsurface. Our new device proved to be fully functional and the results indicate that the possible existence of methanogenic archaea in Martian subsurface habitats cannot be ruled out. (C) 2013 Published by Elsevier Ltd.
KW  - Mars
KW  - Methanogens
KW  - Methane
KW  - Sub-zero temperature (Celsius)
KW  - Wavelength modulation spectroscopy (laser spectroscopy)
Y1  - 2014
U6  - https://doi.org/10.1016/j.pss.2013.08.019
SN  - 0032-0633
VL  - 98
SP  - 198
EP  - 204
PB  - Elsevier
CY  - Oxford
ER  -