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Die vorliegende Doktorarbeit beschäftigt sich mit der experimentellen Studie zweier miteinander verbundener Phänomene: Dem intrinsischen Timing-Jitter in einem supraleitendenden Nanodraht-Einzelphotonen-Detektor (SNSPD) und der Relaxation der Elektronenenergie in supraleitenden Filmen. Supraleitende Nanodrähte auf einem dielektrischen Substrat als mikroskopische Grundbausteine jeglicher SNSPDs stellen sowohl für theoretische als auch für experimentelle Studien komplexe Objekte dar. Die Komplexität ergibt sich aus der Tatsache, dass SNSPDs in der Praxis stark ungeordnete und ultradünne supraleitende Filme verwenden, die eine akustische Fehlanpassung zu dem zugrundeliegenden Substrat aufweisen und einen Nichtgleichgewichts-Zustand implizieren. Die Arbeit untersucht die Komplexität des am weitesten in der SNSPD Technologie verbreiteten Materials, Niobnitrid (NbN), indem verschiedene experimentelle Methoden angewandt werden. Als eine mögliche Anwendung der SNSPD-Technologie wird ein Prototyp eines dispersiven Raman-Spektrometers mit Einzelphotonen-Sensitivität demonstriert. This Ph.D. thesis is based on the experimental study of two mutually interconnected phenomena: intrinsic timing jitter in superconducting nanowire single-photon detectors (SNSPDs) and relaxation of the electron energy in superconducting films. Microscopically, a building element of any SNSPD device, a superconducting nanowire on top of a dielectric substrate, represents a complex object for both experimental and theoretical studies. The complexity arises because, in practice, the SNSPD utilizes strongly disordered and ultrathin superconducting films, which acoustically mismatch with the underlying substrate, and implies a non-equilibrium state. This thesis addresses the complexity of the most conventional superconducting material used in SNSPD technology, niobium nitride (NbN), by applying several distinct experimental techniques. As an emerging application of the SNSPD technology, we demonstrate a prototype of the dispersive Raman spectrometer with single-photon sensitivity.

Atomic oxygen is a main component of the mesosphere and lower thermosphere of the Earth, where it governs photochemistry and energy balance and is a tracer for dynamical motions. However, its concentration is extremely difficult to measure with remote sensing techniques since atomic oxygen has few optically active transitions. Current indirect methods involve photochemical models and the results are not always in agreement, particularly when obtained with different instruments. Here we present direct measurements—independent of photochemical models—of the ground state 3P1 → 3P2 fine-structure transition of atomic oxygen at 4.7448 THz using the German Receiver for Astronomy at Terahertz Frequencies (GREAT) on board the Stratospheric Observatory for Infrared Astronomy (SOFIA). We find that our measurements of the concentration of atomic oxygen agree well with atmospheric models informed by satellite observations. We suggest that this direct observation method may be more accurate than existing indirect methods that rely on photochemical models. Atomic oxygen concentrations in the upper atmosphere can be measured directly with an airborne terahertz heterodyne spectrometer. This approach is probably more accurate than indirect estimates from photochemical models, according to a comparison of the two methods.

Third-order non-linearities are important because they allow control over light pulses in ubiquitous high-quality centro-symmetric materials like silicon and silica. Degenerate four-wave mixing provides a direct measure of the third-order non-linear sheet susceptibility χ(3)L (where L represents the material thickness) as well as technological possibilities such as optically gated detection and emission of photons. Using picosecond pulses from a free electron laser, we show that silicon doped with P or Bi has a value of χ(3)L in the THz domain that is higher than that reported for any other material in any wavelength band. The immediate implication of our results is the efficient generation of intense coherent THz light via upconversion (also a χ(3) process), and they open the door to exploitation of non-degenerate mixing and optical nonlinearities beyond the perturbative regime., Light: Science & Applications, 10 (1), ISSN:2047-7538

In high-energy physics, the Higgs field couples to gauge bosons and fermions and gives mass to their elementary excitations. Experimentally, such couplings can be inferred from the decay product of the Higgs boson, i.e., the scalar (amplitude) excitation of the Higgs field. In superconductors, Cooper pairs bear a close analogy to the Higgs field. Interaction between the Cooper pairs and other degrees of freedom provides dissipation channels for the amplitude mode, which may reveal important information about the microscopic pairing mechanism. To this end, we investigate the Higgs (amplitude) mode of several cuprate thin films using phase-resolved terahertz third harmonic generation (THG). In addition to the heavily damped Higgs mode itself, we observe a universal jump in the phase of the driven Higgs oscillation as well as a non-vanishing THG above Tc. These findings indicate coupling of the Higgs mode to other collective modes and potentially a nonzero pairing amplitude above Tc., Interaction between Cooper pairs and other collective excitations may reveal important information about the pairing mechanism. Here, the authors observe a universal jump in the phase of the driven Higgs oscillations in cuprate thin films, indicating the presence of a coupled collective mode, as well as a nonvanishing Higgs-like response at high temperatures, suggesting a potential nonzero pairing amplitude above Tc.

We analyze the effect of different types of fluctuations in internal electron energy on the rates of dark and photon counts in straight current-carrying superconducting nanowires. Dark counts appear due to thermal fluctuations in statistically independent cells with the effective size of the order of the coherence length; each count corresponds to an escape from the equilibrium state through an appropriate saddle point. For photon counts, spectral broadening of the deterministic cut off in the spectra of the detection efficiency can be phenomenologically explained by local thermal fluctuations in the electron energy within cells with the same effective volume as for dark counts.

1 Introduction The increasing interest in Laser-induced breakdown spectroscopy (LIBS) for space-exploration is confirmed by two more LIBS instruments, SuperCam aboard NASA’s Mars 2020 mission and MarsCoDe as part of China’s Tianwen 1 mission, being launched towards Mars this summer [1, 2]. SuperCam will be the follow-up of the ChemCam instrument, which has been successfully analysing the Martian surface since its landing in 2012 [3]. In 2019, another LIBS instrument has been launched heading for the Moon [4], but did unfortunately not accomplish a soft landing. LIBS is a fast and versatile elemental analysis technique. It is based on laser ablation and needs only optical access to the target. For LIBS, a laser pulse is tightly focused onto the sample, where a small portion of material is ablated and excited into a plasma of neutral atoms, ions and electrons. The plasma emits continuum radiation from bremsstrahlung and electron-ion recombination, together with discrete emission lines from the species in the plasma. The latter allow for identification of the chemical elements contained in the plasma, and therefore in the sample. 2 Challenging elements in LIBS In general, all elements of the periodic table are detectable with LIBS. Some of them, however, have their strongest emission lines outside of the typically observed spectral range from approx. 240 to 800 nm. As the emission intensity of a spectral line strongly depends on, amongst other factors, the population density of the transition’s upper level, transitions between lower energy levels are typically strong. For neutral S, the fundamental ground state transition is located at 180.7 nm, while Cl atoms have their strong ground state transitions between 133 and 138 nm. Both elements are therefore expected to be well detectable in the vacuum-UV (VUV) range below 200 nm. 3 VUV-LIBS VUV-LIBS means the emission of the plasma is detected in the VUV spectral range. In terrestrial environment, this range is obscured due to absorption by O2 and H2O vapour from the atmosphere. VUV absorption in CO2 and CH4 further reduces the applicability of VUV-LIBS on e.g. Mars or Titan. For celestial bodies without a significant atmosphere, however, the predicted high emission intensities in the VUV range for otherwise challenging elements like S and Cl could be exploited to increase the sensitivity for these elements. One drawback of LIBS in a very low pressure environment is the short life time of the plasma and its relatively low intensity. While the reduced atmospheric pressure on Mars in the order of 1 kPa is beneficial for LIBS and produces a large and bright plasma, the low confinement and therefore low probability for collisions of the plasma species at below 10 Pa leads to a short-living and dim plasma [5]. Thus, the sensitivity of LIBS in vacuum is naturally lower, and it could be even more crucial for mission instruments on bodies without atmosphere to make use of the stronger VUV emission lines. VUV-LIBS is readily used in industrial applications, e.g. for S detection in steel [6]. There, laser pulse energies of several hundreds of millijoules, multi-pulse configurations, and purge gas atmospheres are used to compensate for atmospheric absorption and the reduced emissivity of vacuum plasmas, thereby yielding limits of detection in the order of 10-100 ppm. For space exploration, VUV-LIBS has not yet been extensively studied. Radziemski et al. investigated the applicability of VUV-LIBS for use on Mars, using components realistic for a mass-, size- and power-constrained space instrument [7]. They noted significant suppression of the strongest Cl lines in the 130-140 nm range due to the CO2 atmosphere, while at the same time benefiting from the LIBS-favourable pressure. 4 Experimental Details Our set-up is built around a H+P vacuum spectrometer covering the range of 100-300 nm, see Figure 1. The plasma is excited with a pulsed Nd:YAG laser (1064 nm, up to 40 mJ, 6 ns), which is focused vertically onto the sample. The sample is contained in a vacuum chamber, directly flanged to the spectrometer. The radiation emitted by the plasma is coupled into the spectrometer using an off-axis parabolic mirror. The mirror currently limits the spectral range to >120 nm. The whole system is operated at a pressure of ≤1 mPa. The samples analysed in this study are lunar simulants (Exolith LHS-1 and LMS-1 [8]) mixed with different amounts of pure sulfur, different sulfates, or sodium chloride. They have been prepared in-house using mortar and pestle, and a hydraulic press. The resulting atomic fractions of S and Cl range from 0.5 to 4.0 %. 5 Results We successfully detected S in lunar simulant matrices, using the S I emission line at 180.7 nm. Example spectra for Na2SO4 in LHS-1 at 0.5 and 1.6 at% S are shown in Figure 2. Besides Al, Si and O emission lines from the matrix material, the S I emission line is clearly visible already at those low concentrations. Univariate calibration curves suggest a linear relationship between S concentration and emission intensity for low concentrations. The Cl I emission lines around 135 nm spectrally overlap with Si II emission, but a change in their intensity upon changes in the Cl concentration is still recognizable. 6 Summary and Conclusion S and Cl have been detected in lunar simulant matrices at atomic fraction levels in the order of 1 %. For low concentrations of S, we found a linear relationship between S concentration and LIBS signal with a univariate approach. These results are promising for improved detectability of volatiles in space exploration, which are usually hard to detect with conventional LIBS in the spectral range of 240-800 nm. Besides S and Cl, emission lines of Al, Fe, Si and O have been identified. References [1] Wiens et al., Spectroscopy, 32, 5 (2017). [2] Ren et al., EPSC2018, id EPSC2018-759-2 (2018). [3] Maurice et al., J. Anal. At. Spectrom., 31, 863 (2016). [4] Laxmiprasad et al., Advances in Space Research, 52, 332 (2013) [5] Knight et al., Applied Spectroscopy, 54, 331 (2000). [6] Sturm et al., Applied Spectroscopy, 54, 1275 (2000). [7] Radziemski et al., Spectrochim. Acta B, 60, 237 (2005). [8] Britt and Cannon, NESF2019, 82 (2019).

© 2016 IEEE. Teams of mobile robots will play a crucial role in future missions to explore the surfaces of extraterrestrial bodies. Setting up infrastructure and taking scientific samples are expensive tasks when operating in distant, challenging, and unknown environments. In contrast to current single-robot space missions, future heterogeneous robotic teams will increase efficiency via enhanced autonomy and parallelization, improve robustness via functional redundancy, as well as benefit from complementary capabilities of the individual robots. In this letter, we present our heterogeneous robotic team, consisting of flying and driving robots that we plan to deploy on scientific sampling demonstration missions at a Moon-analogue site on Mt. Etna, Sicily, Italy in 2021 as part of the ARCHES project. We describe the robots' individual capabilities and their roles in two mission scenarios. We then present components and experiments on important tasks therein: automated task planning, high-level mission control, spectral rock analysis, radio-based localization, collaborative multi-robot 6D SLAM in Moon-analogue and Mars-like scenarios, and demonstrations of autonomous sample return.

Introduction With the confirmation of water ice in the lunar polar regions [1], the Moon has recently come into the focus of attention of international space agencies again. Volatiles, specifically water and hydrogen, are important resources both for life support and for potential applications as fuels and propellants for spacecraft. In-situ resource utilization (ISRU) of volatiles could significantly reduce the costs of a sustained presence on the Moon and could be beneficial for the future human deep space exploration of the solar system [2]. The detection of volatiles is therefore an important scientific goal for future robotic missions to the Moon. The LUVMI-X project (Lunar Volatiles Mobile Instrumentation – Extended) is developing an initial system design as well as payload and mobility breadboards for the detection of volatiles in the lunar polar region on a small, lightweight rover [3]. The LUVMI-X rover is shown in Figure 1. One proposed scientific payload is VOILA (Volatiles Identification by Laser Ablation), which is jointly developed by OHB System AG (OHB), Laser Zentrum Hannover (LZH), and the German Aerospace Center’s Institute of Optical Sensor Systems (DLR-OS). VOILA will use laser-induced breakdown spectroscopy (LIBS) to analyze the elemental composition of the lunar surface, with a special focus on detecting and quantifying hydrogen and oxygen as indicators for water. LIBS is a versatile technique that requires only optical access to its target [4]. A LIBS spectrum is obtained within seconds, making it well-suited for quick analyses of multiple targets in proximity to the rover. LIBS was first used in space by the ChemCam instrument on board NASA’s Curiosity rover on Mars [5, 6]. The first LIBS instrument on the Moon was supposed to operate on board the Pragyan rover of India’s Chandrayaan-2 mission [7]. However, the Chandrayaan-2 lander failed a soft landing in September 2019. Here, we present a summary of the VOILA instrument design and its intended capabilities for volatiles detection at the lunar south pole. Instrument Design With an expected mass of about 3 kg, VOILA is designed to be more lightweight than the ChemCam instrument, but heavier and slightly more complex than the LIBS instrument designed for the Chandrayaan-2 mission. It will include an optical head with a focusing mechanism designed for working distances between 30 cm and 50 cm, which allows for compensation of uneven terrain or different rover configurations. The optical head is mounted at the front of the rover body and can rotate horizontally to select multiple targets of interest at each rover location. VOILA uses an actively Q-switched pulsed Yb:YAG laser developed by LZH with a pulse energy of at least 15 mJ at a wavelength of 1030 nm to ablate sample material, generating a laser-induced plasma that can be spectrally analyzed. The VOILA spectrometer will have a wavelength range from 350 nm to 790 nm at a spectral resolution of about 0.5 nm, thereby covering atomic and ionic emission lines of the major rock forming elements (O, Si, Al, Fe, Mg, Ca, Na, K, Ti) and of hydrogen. LIBS measurements with VOILA are intended for the analysis of the topmost lunar surface layers. Simple depth profiling within millimeters could be achieved by repeated ablation of the same location on the surface. A single shot is expected to produce a crater of several millimeters depth due to the force of the outgoing shockwave in the regolith. Laboratory Studies Preliminary LIBS studies in near-vacuum (0.1 Pa of air) were made with the high-resolution LIBS setup at DLR-OS to determine the VOILA instrument requirements. Figure 2 shows a LIBS spectrum of lunar regolith simulant Exolith LMS-1 in which all major rock forming elements could be observed within 350 nm to 790 nm. A laser energy of 15 mJ/pulse was found to produce a very intense plasma when focused to a spot of 300 µm diameter. For a basalt/gypsum mixture with a water concentration of about 1.5 wt%, the H I line at 656.3 nm was successfully detected, see Figure 3. The signal to noise ratio is about 4.3 for this line, indicating that even lower concentrations can be detected. Furthermore, the high-resolution echelle spectrometer used for the measurements has a low throughput that will be exceeded by the VOILA instrument itself. Conclusion VOILA is a new LIBS instrument for the detection of volatiles at the lunar south pole. Initial experiments show that LIBS can be employed at low pressures and that clear signals of all major rock-forming elements and of hydrogen can be obtained in the specified spectral range of VOILA. The pulse energy of VOILA is at least 15 mJ, which is achievable by the laser prototype developed by LZH. The successful detection of hydrogen is promising, but the instrument should also be qualified with measurements of real water ice at low concentrations. Future studies should also investigate whether water ice can be distinguished from other hydrogen and oxygen sources. New results obtained with the VOILA demonstration setup developed by OHB, LZH and DLR will be presented at the conference. Acknowledgments This research was funded by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 822018. References [1] Li S. et al. (2018) PNAS, 36, 8907–8912. [2] Anand M. et al. (2012) Planet. Space Sci., 74, 42–48. [3] Gancet J. et al. (2019) ASTRA 2019. [4] Knight A. K. et al. (2000) Appl. Spectrosc., 54, 331–340. [5] Maurice S. et al. (2012) Space Sci. Rev., 170, 95–166. [6] Wiens R. C. et al. (2012) Space Sci. Rev., 170, 167–227. [7] Laxmiprasad A. S. et al. (2013) Adv. Space Res., 52, 332–341. [8] Lasue J. et al. (2012) J. Geophys. Res., 117, E1.

In this study, a conceptually different approach for investigating magnetic phase transitions in ultra-thin films is presented. THz emission from a laser-excited material is used to monitor the magnetization dynamics during the laser-driven antiferromagnetic to ferromagnetic transition in FeRh. The emitted THz signal is calibrated against static magnetometry data measurements, giving a direct measure of the absolute magnetic moment of the sample on the sub-picosecond timescale. The technique is, therefore, highly complementary to conventional timeresolved experiments such as time resolved magneto-optic Kerr effect (MOKE) or x-ray magnetic circular dichroism. It furthermore allows to determine the degree of magnetization of materials from the distance.

We report on the inelastic-scattering rate of electrons on phonons and relaxation of electron energy studied by means of magnetoconductance, and photoresponse, respectively, in a series of strongly disordered superconducting NbN films. The studied films with thicknesses in the range from 3 to 33 nm are characterized by different Ioffe-Regel parameters but an almost constant product q_Tl(q_T is the wave vector of thermal phonons and l is the elastic mean free path of electrons). In the temperature range 14-30 K, the electron-phonon scattering rates obey temperature dependencies close to the power law 1/\tau_{e-ph} \sim T^n with the exponents n = 3.2-3.8. We found that in this temperature range \tau_{e-ph} and n of studied films vary weakly with the thickness and square resistance. At 10 K electron-phonon scattering times are in the range 11.9-17.5 ps. The data extracted from magnetoconductance measurements were used to describe the experimental photoresponse with the two-temperature model. For thick films, the photoresponse is reasonably well described without fitting parameters, however, for thinner films, the fit requires a smaller heat capacity of phonons. We attribute this finding to the reduced density of phonon states in thin films at low temperatures. We also show that the estimated Debye temperature in the studied NbN films is noticeably smaller than in bulk material., Comment: 23 pages, 6 figures

We present an optically pumped terahertz gas laser, which is based on a mid-infrared quantum-cascade laser as a pump source, a transversely pumped standing wave resonator, and 15NH3 as a gain medium. We observe several laser lines around 4.5 THz, corresponding to rotational transitions in the ν2 band of ammonia. So far, these are the highest frequencies obtained from a QCL-pumped THz gas laser. The involved molecular transitions are unambiguously identified by high-resolution spectroscopy.

The Moon has recently come into the focus of attention of international space agencies again. Concepts for the establishment of a long-term human presence on the Moon have been proposed, such as the Moon Village concept championed by ESA and NASAs lunar outpost concepts as part of the Artemis program. One reason for this renewed interest in the Moon was the discovery of water ice in the lunar polar regions by the Chandrayaan-1 mission. Water and other volatiles are important resources both for life support and for potential applications as fuels and propellants for spacecraft. In-situ resource utilization (ISRU) of volatiles could significantly reduce the costs of a sustained presence on the Moon and could also be beneficial for the future human exploration of the solar system. The detection of volatiles like water is therefore an important scientific goal for future robotic missions to the Moon. The LUVMI-X project (Lunar Volatiles Mobile Instrumentation Extended) is developing an initial system design as well as payload and mobility breadboards for the detection of volatiles in the lunar polar region on a small, lightweight rover. One of them is the LIBS instrument VOILA (Volatiles Identification by Laser Analysis). LIBS is a technique that requires only optical access to its target. A LIBS spectrum is obtained within seconds, making it well-suited for quick analyses of multiple targets in proximity to the rover. LIBS was first used in space by the ChemCam instrument on board Curiosity of NASAs Mars Science Laboratory mission. With SuperCam on board NASAs Mars2020 rover and MarsCoDe on board Chinas HX-1 rover, two more LIBS instruments are headed for Mars in 2020. The first LIBS instrument on the Moon was supposed to operate on board the Pragyan rover of Indias Chandrayaan-2 mission, but the lander crashed onto the lunar surface during descent in September 2019. In this study, we demonstrate the potential of LIBS for the detection of volatiles on the lunar surface. The influence of instrument parameters such as the pulse energy of the laser and the spectral coverage of the spectrometer on the obtained spectra is analyzed and the feasibility of hydrogen quantification is investigated in mixed samples of varying composition.

BIOLEX is a concept designed for in situ science on the Moon or in its orbit. As heritage of the polar and space experiment BIOMEX (Biology and Mars Experiment) on the ISS it is a more developed concept. Measurement operations on an exposure platform as well as within a micro-greenhouse device are part of this concept. The goal is to investigate the use of lunar resources as well as to analyse the stability of biomolecules as potential biosignatures serving as reference for future space exploration missions to Mars and the icy ocean moons in the outer solar system. Astrobiological exploration of the solar system is a priority research area such as emphasized by the European Astrobiology Roadmap (AstRoMap). It is focusing on several research topics, such as "Habitability" and on "Biomarkers for the detection of life". Therefore, "space platforms and laboratories", such as the EXPOSE setup installed outside the ISS, are essential to gain more knowledge on space- and planetary environments, which might be an essential basis for improvement of the robotic and human interplanetary exploration (Moon, Mars, Encedalus, Titan and Europa). In reference to these exposure platforms a new generation of hardware is needed to be installed in the lunar orbit or directly on the Moon. The BIOLEX is representing by its LOGOS (Lunar Organisms, Geo-microbiology and Organics Space Experiment) cubes such a concept combining the life detection topics with topics relevant to autonomous life supporting systems. A combination of a sample exposure device and a microhabitat for plants and microorganisms could address a tremendous number of questions from astrobiology and life sciences. The main scientific objectives for the use of BIOLEX-LOGOS cubes are: (i) in situ measurements by spectroscopy methods (such as Raman, IR, UV/VISspectroscopy) for analysis of biosignatures and their stability what is relevant for support of future life detection missions on Mars and the icy moons in the outer solar system); (ii) in situ measurements of environmental conditions (radiation, pressure/vacuum, temperature, pH, humidity) in micro-modules or compartments in reference to planned micro-habitat experiments placed on the Moon or incorporated on an exposure facility in orbit; (iii) in situ measurements of microorganisms’ activity in micro-modules / compartments in reference to planned microhabitat experiments placed on the moon or incorporated in the exposure facility in orbit. In reference to these scientific ideas the Moon is an excellent platform to operate different space experiments which will be of relevance for astrobiology, life sciences and human space missions. BIOLEX tries to fulfil a large number of scientific investigations in reference to these disciplines. The lunar environment is much harsher compared to Mars; and tests on biomolecules in this environment could provide information on their stability and therefore on the value to be used as reference for future space missions to Mars or the icy ocean moons in the outer solar system. Resources of the Moon such as the regolith or the freely available radiation on the surface could be tested by using them in a micro-greenhouse. Within this greenhouse different filters could test the optimal spectra range of the radiation.

The understanding of how spins move and can be manipulated at pico- and femtosecond timescales has implications for ultrafast and energy-efficient data-processing and storage applications. However, the possibility of realizing commercial technologies based on ultrafast spin dynamics has been hampered by our limited knowledge of the physics behind processes on this timescale. Recently, it has been suggested that inertial effects should be considered in the full description of the spin dynamics at these ultrafast timescales, but a clear observation of such effects in ferromagnets is still lacking. Here, we report direct experimental evidence of intrinsic inertial spin dynamics in ferromagnetic thin films in the form of a nutation of the magnetization at a frequency of ~0.5 THz. This allows us to reveal that the angular momentum relaxation time in ferromagnets is on the order of 10 ps. Inertial dynamics are observed in a ferromagnet. Specifically, a nutation is seen on top of the usual spin precession that has a lifetime on the order of 10 picoseconds.

A first step towards realization, a small satellite study for OSAS (Oxygen Spectrometer for Atmospheric Science) has been performed based on Concurrent Engineering methods.

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.

The Raman Laser Spectrometer (RLS) instrument on board of the future ESAs ExoMars mission will analyze micron-sized powder samples in a low pressure atmosphere. Such micron-sized polycrystalline solid particles might be heated by the laser during the Raman measurements. Here, we report on the temperature-induced alteration of Raman spectra from micron-sized polycrystalline solid particles by comparing Raman spectra on silicon and the rock forming minerals olivine and pyroxene taken at different laser intensities and different ambient temperatures. Our analyses indicate that laser-induced heating results in both broadening and shifting of characteristic Raman lines in the Stokes and anti-Stokes spectral regions. For elementary crystalline silicon a significant local temperature increase and relevant changes in Raman spectra have been observed in particles with median sizes below 250 µm. In comparison, significantly weaker laser-induced Raman spectral changes were observed in more complex rock-forming silicate minerals; even for lower grain sizes. Laser power densities realized in the RLS ExoMars instrument should cause only low local heating effects and, thus, negligible frequency shifts of the major Raman lines in common silicate minerals such as olivine and pyroxene.

Molecular emissions in LIBS can be used to detect elements that do not have strong emission lines, such as Cl and F. This is interesting for Martian exploration, where Cl and F offer important clues about past environments. In this study, we investigate the relationship between the reactant concentrations and the intensities of the molecular emissions of MgCl, CaCl, and CaF. The intensities of CaCl and CaF emissions are well-described by the non-equilibrium calibration model that is introduced. Plasma imaging experiments show that the molecules only form close to the center, suggesting that the plasma temperature is unexpectedly low there, potentially due to rarefaction and radiative losses.

ChemCam on board the Mars rover Curiosity is the first LIBS instrument on Mars. In 2020,two more LIBS instruments will follow [1,2]. Thus, understanding the capabilities andchallenges of LIBS in Mars’ atmosphere is of high interest. A general challenge of LIBS is self-absorption (SA). The effect of SA depends on the atmospheric conditions. In Earth’satmosphere SA affects the intensities of the emission lines strongly and breaks the linearityof calibration curves which limits their accuracy [3]. While SA is expected to be lower inMartian conditions, no extensive studies on this have been reported. In this study weinvestigate SA in LIBS spectra acquired in simulated Martian atmospheric conditions. LIBSspectra of salts are obtained with two different setups: A high-resolution LIBS setup with ahigh spectral range and a plasma imaging setup allowing for spatially resolvedmeasurements of the full plasma at a selected small spectral range. In measurements madewith the plasma imaging setup, the effect of SA on the Ca(II) doublet at 393 nm and 396 nmcan be observed. Fig. 1A shows the intensity ratio of the two emission lines for line-of-sightmeasurements through the plasma plume at different distances from the plasma axis. Withnegligible SA the ratio would be 2.1. We find a strong influence of SA, especially for largeeffective path lengths through the plasma center. For the calculation of the SA effect inspectra of the high-resolution LIBS setup, the plasma is modelled as a two-layer plasma inlocal thermal equilibrium. Temperature, electron density, and effective path length of eachlayer are varied and the resulting simulated spectra are compared to the measurements tofind the best fit, see Fig. 1B. From the values of the best fit we find that many strong emissionlines are significantly affected by SA, even though the effect is not obvious from the lineprofiles because of the instrumental broadening.

We demonstrate a technique to simultaneously stabilize the frequency and output power of a terahertz quantum-cascade laser. The technique exploits frequency and power variations upon near-infrared excitation and does not require an external terahertz optical modulator. By locking the frequency to a molecular absorption line, we obtain a linewidth of about 260 kHz and root-mean-square power fluctuations as low as 0.03%.

We present an efficient and robust source of photons at the $^{87}$Rb D1-line (795 nm) with a narrow bandwidth of $\delta=226(1)$ MHz. The source is based on non-degenerate, cavity-enhanced spontaneous parametric down-conversion in a monolithic optical parametric oscillator far below threshold. The setup allows for efficient coupling to single mode fibers. A heralding efficiency of $\eta_{\mathrm{heralded}}=45(5)$ % is achieved, and the uncorrected number of detected photon pairs is $3.8 \times 10^{3}/(\textrm{s mW})$. For pair generation rates up to $5\times 10^{5}/$s, the source emits heralded single photons with a normalized, heralded, second-order correlation function $g^{(2)}_{c} 2$ GHz by applying mechanical strain., Comment: 6 pages, 4 figures

Laser-Induced Breakdown Spectroscopy (LIBS) is an increasingly important tool in the exploration of Mars. The detection of Cl and F with LIBS has been a challenge due to their low-intensity emission lines. The detection via molecular emissions has been proposed as a way to enhance the level of detection for halogens. In this study, the suitability of molecular emissions of CaCl, CaF, MgCl, and MgF in LIBS spectra for the detection and quantification of Cl and F is investigated. Experiments are made in simulated Martian ambient conditions and numerical simulations are used to explain the observations. The CaCl and CaF emissions can lead to an improved detection while MgCl and MgF emissions are very weak and do not improve the limit of detection for these Cl and F.

Near-infrared optical excitation enables wideband requency tuning of terahertz quantum-cascade lasers. In this work, we demonstrate the feasibility of the approach for molecular laser absorption spectroscopy. We present a physical model which explains the observed frequency tuning characteristics by the optical excitation of an electron-hole plasma. Due to an improved excitation configuration as compared to previous work, we observe a single-mode continuous-wave frequency coverage of as much as 40 GHz for a laser at 3.1 THz. This represents, for the same device, a ten-fold improvement over the usually employed tuning by current. The method can be readily applied to a large class of devices.

LIBS has been proven very useful for in-situ geochemical analysis on the Martian surface [1]. It has also been proposed for future missions to explore other bodies of the Solar System [e.g. 2]. For this reason, it has become more important to understand the capabilities and challenges of LIBS under atmospheric conditions that are different from Earth. There is also a high interest in calibration-free LIBS (CF-LIBS) due to the highly versatile measuring conditions in planetary exploration. In this study, we have developed a method to assist the analysis of LIBS spectra acquired under different atmospheric conditions corresponding to different extraterrestrial mission scenarios. The method is developed from first principles and without resorting to measurements on calibration standards, similar to CF-LIBS [3]. Our approach follows from the same theory and assumptions as the standard approaches of CF-LIBS, such as the construction of Boltzmann plots, but many labor intensive steps are automated. Assuming an optically thin plasma in local thermal equilibrium (LTE) with assumed distributions of electron density and temperature, a linear relationship exists between the intensities of the atomic emission lines and the elemental concentrations. Our approach is to set up a system of linear equations between the extracted integrated peak intensities, in a given spectrum, and the theoretically predicted peak-intensities by the Saha-Boltzmann equation. From this system of equations, the concentrations are solved semi-analytically by minimizing the residuals between the peak-intensities. The minimization is repeated using different simply parameterized functions of the electron densities and temperatures, i.e. the plasma parameters. We evaluate the applicability of the method to data acquired under different atmospheric conditions. Moreover, we investigate the consequences of different assumptions and distributions of the electron density and temperature to the results and discuss the limitations of the approach. [1] Maurice et.al., Mars. J. Anal. At. Spectrom. (2016). [2] Arp et.al., Spectrochimica Acta Part B: Atomic Spectroscopy. (2004). [3] Tognoni et.al., Spectrochimica Acta Part B: Atomic Spectroscopy. (2009).

Raman spectroscopy is a promising method for space exploration, especially when searching for past or present life. The weak Raman signal is easily superseeded by comparably strong sunlight, which is necessary for electric power supply and temerature regulation of the spacecraft carrying the instrument. Therefore, it is often claimed that only a pulsed operating mode is feasible for in-situ studies on celestian bodies. Pulsed systems, however, imply a much more complex instrument design and thus higher costs and develepmont effort together with a higher risk of failure. In this work, we investigated the capabilities and limits of continuous wave Raman spectroscopy in daylight. The simulated sunlight has been adjusted to match the solar irradiance in Mars-distance from the sun for the visible spectral range. Surprisingly promising results have been found for measurements in the shadow of the spacecraft or when using a sun block to avoid direct illumination.

LIBS is an upcoming spectroscopic technique for in-situ space exploration. Some elements, especially the halogens and chalcogens, however, show only weak signal in the commonly detected UV to NIR spectral range. Those elements' strongest emission lines are located in the vacuum ultraviolet range, below 200 nm. On Earth, light in this region is absorbed by oxygen and water vapour from the atmosphere. For celestial bodies without atmosphere, the spectral range of detection could be extended towards the shorter wavelengths and increase detectability for the otherwise challenging elements. In this work we present first results for sulphur detection in Lunar analogue material by analysis of the vacuum-UV fraction of the LIBS signal. Aiming at a future use for space instruments, we conduct our studies in vacuum and with laser parameters feasible for a mission context.

Laser-Induced Breakdown Spectroscopy (LIBS) permits rapid in-situ multi-elemental analysis without sample preparation and with optical access only. It has been proven to be a very useful technique for in-situ geochemical analysis of the surface of Mars. The pressure and composition of the ambient gas affect the formation, the evolution, and the emission of the laser-induced plasma. The reduced plasma confinement is expected to lead to a higher relevance of dynamic processes within the plasma and of temperature gradients within the plasma. We have developed a custom plasma imaging setup which allows us to investigate laser-induced plasmas in simulated Martian atmospheric conditions. Our goal is to provide a better understanding of the particular characteristics of Martian LIBS plasmas, their dynamics and typical spatial and temporal evolution by means of time-resolved plasma imaging.

We demonstrate the feasibility of wideband frequency tuning of terahertz quantum-cascade lasers by spatially well-controlled near-infrared optical excitation. We observe a single-mode continuous-wave frequency coverage of up to 40 GHz for a 3.1 THz laser. This represents a tenfold improvement of the tuning range for the same device as compared to tuning by current. This method is applicable to a wide variety of existing terahertz quantum-cascade lasers.

Cryptoendolithic microbial communities, discovered in the extremely cold, hyper-arid McMurdo Dry Valleys of Antarctica (Friedmann 1982), the most similar terrestrial environments to Mars surface (Wynn-Williams and Edwards 2000; Onofri et al., 2004), have been considered as a candidate in supporting the search of life in Mars exploration. In such harsh conditions, microorganisms grow in airspaces among mineral grains and show some adaptations, as the accumulation of protective pigments and compatible solutes, assuring their survival. In the frame of the Lichen and Fungi experiment (LIFE, P.I. Silvano Onofri; Onofri et al. 2012, 2015), small samples of these communities, were exposed to space, in the EXPOSE-E facility for 1.5 years, with an exposition to vacuum (10-7 to 10-4 Pa) (Horneck et al., 2010), galactic cosmic radiation (≤190mGy) (Berger et al., 2012), and the full spectrum of solar extraterrestrial electromagnetic radiation to which cryptoendolithic microorganisms demonstrated to survive (Scalzi et al., 2012). The search for trace of extant or extinct life is one of the main goals of the future space mission beyond Earth. The future rover missions ExoMars 2020 (ESA-Roscomos) and Mars 2020 (NASA) are exploring chemical and biological indicators of life, called biomarkers. A good biomarker must have a biogenic origin and thus must unequivocally be identified as possible trace of life. The detection of biomarkers on Mars was the aim of BIOMEX (BIOlogy and Mars Experiment) project, in which has been investigated the alteration of different biomarkers, after exposure to space and Mars-like conditions outside the International Space Station. In this contest, the aim of this work was to characterize fungal biomarkers from these exposed rock samples, with different approaches: i) Raman spectroscopy and InfraRed analyses, which has been considered excellent tools for the detection of inorganic and organic molecules, such as microbial pigments and ii) -omics approaches, as lipidomic and metabolomic techniques, performed to detect biological macromolecules and to determine their stability after space exposure. The focus of lipidomics and metabolomics has been on biomarker discovery, with the aim of identifying metabolites that are correlated with environmental exposures. The results suggest that microbial molecules can be detected through different techniques. In particular, our attention was focused on pigments, such as melanin and carotenoids that maintain their stability also after 1.5 years of space exposure. These results are of importance for the upcoming life-detection missions on Mars finalized for the search for past, extant or extinct life outside the Earth.

International audience; Transient-type stimulated emission in the terahertz (THz) frequency range has been achieved from phosphorus doped silicon crystals under optical excitation by a few-picosecond-long pulses generated by the infrared free electron lasers FELIX and CLIO. The analysis of the lasing threshold and emission spectra indicates that the stimulated emission occurs due to combined population inversion based lasing and stimulated Raman scattering. Giant gain has been obtained in the optically pumped silicon due to large THz cross sections of intracenter impurity transitions and resonant intracenter electronic scattering. The transient-type emission is formed under conditions when the pump pulse intervals exceed significantly the photon lifetime in the laser resonator.

We report on circuit simulation, modeling, and characterization of field-effect transistor based terahertz (THz) detectors (TeraFETs) with integrated patch antennas for discrete frequencies from 1.3 to 5.7 THz. The devices have been fabricated using a standard 90-nm CMOS technology. Here, we focus in particular on a device showing the highest sensitivity to 4.75-THz radiation and its prospect to be employed for power monitoring of a THz quantum cascade laser used in a heterodyne spectrometer GREAT (German REceiver for Astronomy at Terahertz frequencies). We show that a distributed transmission line based detector model can predict the detector's performance better than a device model provided by the manufacturer. The integrated patch antenna of the TeraFET designed for 4.75 THz has an area of $13\times 13$ $\mathrm{\mu }$ m $^2$ and a distance of 2.2 $\mu$ m to the ground plane. The modeled radiation efficiency at the target frequency is 76% with a maximum directivity of 5.5, resulting in an effective area of 1750 $\mu$ m $^2$ . The detector exhibits an area-normalized minimal noise-equivalent power of 404 pW/ $\sqrt{\mathrm{Hz}}$ and a maximum responsivity of 75 V/W. These values represent the state of the art for electronic detectors operating at room-temperature and in this frequency range.

The question "Are we alone in the Universe?" is perhaps the most fundamental one that affects mankind. How can we address the search for life in our Solar System? Mars, Enceladus and Europa are the focus of the search for life outside the terrestrial biosphere. While it is more likely to find remnants of life (fossils of extinct life) on Mars because of its past short time window of the surface habitability, it is probably more likely to find traces of extant life on the icy moons and ocean worlds of Jupiter and Saturn. Nevertheless, even on Mars there could still be a chance to find extant life in niches near to the surface or in just discovered subglacial lakes beneath the South Pole ice cap. Here, the different approaches for the detection of traces of life in the form of biosignatures including prebiotic molecules will be presented. We will outline the required infrastructure for this enterprise and give examples of future mission concepts to investigate the presence of life on other planets and moons. Finally, we will provide suggestions on methods, techniques, operations and strategies for preparation and realization of future life detection missions.

LIBS is an increasingly important tool in the exploration of Solar System bodies. It has met great success on Mars with the ChemCam instrument on board of the NASA Mars Science Laboratory. SuperCam, the successor of the ChemCam instrument, will use LIBS in combination with Raman and fluorescence spectroscopy on the Mars2020 mission. The Chandrayaan-2 mission of India will feature a lunar rover with an on-board LIBS instrument. Additionally, concepts for LIBS instruments that could be used on other planetary bodies in the Solar System have been proposed. The reduced atmospheric pressure on many Solar System bodies has a strong influence on the LIBS plasma. At lower pressures, the plasma plume becomes more optically thin, resulting in less plasma shielding and more material ablation. At the same time, the lifetime and the emissivity of the plasma plume decrease as it expands more quickly. This tradeoff yields maximum signal intensities at around 10 mbar, close to Martian atmospheric pressure. Below 1 µbar, the pressure of the LIBS plasma is significantly larger than the atmospheric pressure and a stable low-intensity plateau is reached. Laboratory studies at this pressure should therefore be a good approximation of planetary bodies without an atmosphere. In this study, we investigate plasma plumes of geological samples at pressures between 1 µbar and 1 bar with a custom time-resolved plasma imaging setup. We compare spatial distributions of atomic, ionic and molecular species inside the expanding plasma plumes for different pressures and calculate profiles for the temperature and the electron density. The results will indicate which approximations and assumptions still hold in low-pressure conditions, which is important for the analysis of LIBS data from Mars and other planetary exploration missions.

We report on the Doppler-free saturation spectroscopy of a molecular transition at 3.3 THz based on a quantum-cascade laser and an absorption cell in a collinear pump-probe configuration. A Lamb dip with a sub-Doppler linewidth of 170 kHz is observed for a rotational transition of HDO. We found that a certain level of external optical feedback is tolerable as long as the free spectral range of the external cavity is large compared to the width of the absorption line.

LIBS is a very useful tool for robotic in-situ space exploration because of its remote capability and the omission of sample preparation, and was extraterrestrially employed for the first time on NASAs Mars Science Laboratory [1]. Space missions have severe constraints on size, mass and power consumption limiting the capabilities of the instruments on board in comparison to laboratory instrumentation on Earth. The German Aerospace Center is currently developing a miniaturized LIBS instrument of ~1 kg in mass with a low power laser of approximately 5 mJ pulse energy for pioneering missions to explore planets, moons and asteroids in the Solar System. While Martian atmospheric conditions are close to ideal for the LIBS technique, low pressure environments such as on most of these bodies are more challenging [2,3]. The instrument has to provide sufficient irradiance to create a suitable plasma for scientific analysis while still meeting the aforementioned limitations on mass and energy. With a prototype miniature LIBS setup, measurements on different materials were conducted. Regolith simulants for the Earths moon and the Martian moon Phobos [4] were investigated as well as pure salts to test the capabilities for major element detection as well as for volatiles. All experiments were performed at pressures of

We report on molecular spectroscopy with a terahertz quantum-cascade laser (QCL). The frequency of the QCL is tuned by illuminating one of its facets using a near-infrared laser. A tuning range of 17 GHz is achieved for continuous-wave operation.

We report on molecular spectroscopy with a terahertz quantum-cascade laser (QCL). The frequency of the QCL is tuned by illuminating its rear facet using a near-infrared laser. A tuning range of 220 MHz is achieved for continuous-wave operation.

We report on an optically pumped laser where photons are simultaneously generated by population inversion and by stimulated Raman scattering in the same active medium, namely crystalline silicon doped by bismuth (Si∶Bi). The medium utilizes three electronic levels: ground state [|1⟩: 1s(A_{1}) in Si∶Bi], upper [|3⟩: 2p_{±}] and lower [|2⟩: 1s(E)] laser levels. The |1⟩↔|3⟩ and |2⟩↔|3⟩ transitions are optically allowed and the |1⟩↔|2⟩ transition is Raman active. Lasing based on population inversion occurs between the states |3⟩ and |2⟩, while Raman scattering benefits from the Raman-active transition. At high pump power the inversion-based stimulated emission |3⟩→|2⟩ disappears, because electronic scattering from |1⟩ to |2⟩ via a virtual state dominates and the electrons are excited into |2⟩ rather than into |3⟩. Starting as population inversion-based lasing, it ends as stimulated Raman scattering. Our model shows that such a competition occurs on the timescale of the 10-ps-long pump pulse.

Mars and the Jovian and Saturnian moons (Europa and Enceladus) are the next targets to search for life in our Solar System. New life detection instruments are indeed ready to be sent to Mars in 2020 (onboard ESA/Roscomos’s ExoMars2020 and NASA’s Mars2020 rovers) and possibly further. Among them, spectroscopy methods such as Raman or infrared are promising techniques that can give insights on both the mineralogical context and the identification of biosignatures. However, to support and interpret spectroscopic data correctly, as well as to guide future life detection missions, a better understanding of possibly habitable environments and potentially detectable biosignatures is of paramount importance. During the last years extensive field and laboratory investigations focused on demonstrating the capabilities of such technologies to characterize both mineral and biological samples of relevance to Mars but very few assessed potential biosignatures degradation under Mars-like or space-like conditions. To this end we are using samples from ground-based and space exposure experiments, the STARLIFE [1] and the BIOMEX [2] projects, to characterize their Raman and IR signatures after space and Mars relevant stresses. BIOMEX was part of the EXPOSE-R2 mission of the European Space Agency, which allowed a 15-month exposure on the outer side of the International Space Station and STARLIFE is an international campaign to study the role of galactic cosmic radiation in astrobiological systems. A wide range of extremophilic organisms such as cyanobacteria, permafrost green-algae, iron bacteria or methanogens and selected biomolecules exposed under these conditions will help us to define targets for future missions to Mars (and other bodies) carrying Raman, IR or LIBS spectrometers and give further clues about the potential habitability of Mars. We report, as an example, on the preservation potential of cyanobacterial photoprotective pigments (carotenoids) in the Antarctic cyanobacterium Nostoc cf. punctiforme strain CCCryo 231-06 after high doses of gamma irradiation and after space exposure [3]. [1] R. Moeller, M. Raguse, S. Leuko, T. Berger, C.E. Hellweg, A. Fujimori, R. Okayasu, and G. Horneck, Astrobiology, 17, 101–109 (2017). [2] J.-P. de Vera, M. Alawi, T. Backhaus, M. Baqué, D. Billi, U. Böttger, T. Berger, M. Bohmeier, C. Cockell, R. Demets, R. de la Torre Noetzel, H. Edwards, A. Elsaesser, C. Fagliarone, A. Fiedler, B. Foing, F. Foucher, J. Fritz, F. Hanke, et al., Astrobiology, 19, 145–157 (2019). [3] M. Baqué, F. Hanke, U. Böttger, T. Leya, R. Moeller, and J.-P. de Vera, Journal of Raman Spectroscopy, 49, 1617–1627 (2018).