Granular Structure Determined by Terahertz Scattering

Light-scattering in the terahertz region is demonstrated for granular matter. A quantum-cascade laser is used in a benchtop setup to determine the angle-dependent scattering of spherical grains as well as coffee powder and sugar grains. For the interpretation of the form factors for the scattering from single particles one has to go beyond the usual Rayleigh-Gans-Debye theory and apply calculations within Mie theory. In addition to single scattering also collective correlations can be identified and extracted as a static structure factor.Comment: 7 pages, 12 figure

Stabilizing a SiGe BiCMOS Transmitter on a Molecular Absorption Line

In many applications, highly stable frequency references are desired which at the same time take up little volume and consume little power. Transmitters and receivers in SiGe BiCMOS technology can be realized on chip-scale, working at in the THz/Millimeter-wave range where many molecules have strong rotational transitions. We stabilized a SiGe BiCMOS transmitter on a rotational transition of carbon monoxide, reaching stabilities of <1E-10 at 100 s integration

LIBS for prospecting and Raman spectroscopy for monitoring: two feasibility studies for supporting in-situ resource utilization

Laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy are still rather new techniques for in-situ exploration of extraterrestrial planetary surfaces but have shown their suitability and great potential in several successful robotic missions already. Next to serving primary scientific applications, both methods can also be used in the context of in-situ resource utilization (ISRU) such as scouting for wanted substances and the surveillance of extraction processes. Here, we present two laboratory studies conducted in the context of ISRU with a focus on the chain from prospecting to extracting oxygen from lunar regolith. For LIBS, with optimized data processing and combined with state-of-the-art multivariate data analysis approaches, we show the potential of the technique for identifying samples with increased ilmenite content and for elemental quantification. The measurements were done using lunar regolith simulant and low pressures simulating vacuum on atmosphereless bodies such as the Moon. With Raman spectroscopy, we analyzed lunar regolith simulant samples that underwent electrochemical alteration for oxygen extraction and production of metal alloys demonstrating the potential of Raman spectroscopy for ISRU process monitoring. We also discuss the results in a broader context, evaluating the potential of both methods for other aspects of ISRU support.Peer Reviewe

Phonon heat capacity and self-heating normal domains in NbTiN nanostrips

Self-heating normal domains in thin superconducting NbTiN nanostrips with the granular structure were characterized via steady-state hysteretic current–voltage characteristics measured at different substrate temperatures. The temperature dependence and the magnitude of the current, which sustains a domain in equilibrium at different voltages, can only be explained with a phonon heat capacity noticeably less than expected for 3D Debye phonons. This reduced heat capacity coincides with the value obtained earlier from magnetoconductance and photoresponse studies of the same films. The rate of heat flow from electrons at a temperature Te to phonons in the substrate at a temperature TB is proportional to (Tep−TBp) with the exponent p ≈ 3, which differs from the exponents for heat flows mediated by the electron–phonon interaction or by escaping of 3D Debye phonons via the film/substrate interface. We attribute both findings to the effect of grains on the phonon spectrum of thin NbTiN films. Our findings are significant for understanding the thermal transport in superconducting devices exploiting thin granular films.Peer Reviewe

Raman spectra of olivine measured in different planetary environments

Missions to bodies of our solar system are coming up and imply new instrumentation to be applied remotely and in situ. In ESA’s ExoMars mission the Raman Laser Spectrometer (RLS) will identify minerals and organic compounds in Martian surface rocks and soils. Here we present the results of a Raman study of different olivines with variable Fo and Fa contents. We chose olivine because it is a rock forming mineral and is found as an abundant mineral in Martian meteorites. We determined the Raman spectra in different environmental conditions that include vacuum, 8 mbar CO2 atmosphere and temperatures between room temperature and 10 K. These environmental conditions resemble those on asteroids as well as on Mars and Moon. Thus our study investigates the influence of these varying conditions on the position and band width of the Raman lines, which is to be known when such investigations are performed in future space missions

Molecular emission in laser-induced breakdown spectroscopy: An investigation of its suitability for chlorine quantification on Mars

The intensity of the molecular CaCl emission in LIBS spectra is examined in order to evaluate its suitability for the detection of chlorine in a Martian environment. Various mixtures resembling Martian targets with varying Cl content are investigated under simulated Martian conditions. The reactions leading to the formation of CaCl are modeled based on reaction kinetics and are used to fit the measured CaCl band intensities. MgCl bands are also investigated as potential alternatives to CaCl, but no MgCl bands can be identified in samples containing both Mg and Cl. The study confirms that CaCl is well suited for the indirect detection of chlorine, but finds a strong dependence on the concentrations of Ca and Cl in the sample. Spectra from samples with a high chlorine concentration can have low-intensity CaCl emission due to a deficiency of Ca. A qualitative estimate of the sample composition is possible based on the ratio of the band intensity of CaCl to the intensity of Ca emission lines. Time-resolved measurements show that the CaCl concentration in the plasma is highest after about 1 µs

Heterodyne Spectroscopy with a 225 – 255 GHz SiGe BiCMOS Receiver Frontend for Space Applications

Molecular spectroscopy with terahertz heterodyne receivers is an important and widely used method for remote sensing of gases in space, in the Earth's and planetary atmospheres, as well as in the coma of comets. For the use on small satellites, compact and lightweight receivers are needed. We have developed an integrated SiGe BiCMOS receiver frontend that is tunable from 225 to 255 GHz and have characterized it for heterodyne spectroscopy. The double-sideband noise temperature is 11000 K at a local oscillator frequency of 240 GHz and the Allan time is 1 s. With this receiver, we successfully performed heterodyne absorption and emission spectroscopy of acetonitrile in laboratory experiments

High-spectral-resolution terahertz imaging with a quantum-cascade laser

We report on a high-spectral-resolution terahertz imaging system operating with a multi-mode quantum-cascade laser (QCL), a fast scanning mirror, and a sensitive Ge:Ga detector. By tuning the frequency of the QCL, several spectra can be recorded in 1.5 s during the scan through a gas cell filled with methanol (CH3OH). These experiments yield information about the local absorption and the linewidth. Measurements with a faster frame rate of up to 3 Hz allow for the dynamic observation of CH3OH gas leaking from a terahertz-transparent tube into the evacuated cell. In addition to the relative absorption, the local pressure is mapped by exploiting the effect of pressure broadening