The Ganymede Laser Altimeter (GALA) for the Jupiter Icy Moons Explorer (JUICE): Mission, science, and instrumentation of its receiver modules

The Jupiter Icy Moons Explorer (JUICE) is a science mission led by the European Space Agency, being developed for launch in 2023. The Ganymede Laser Altimeter (GALA) is an instrument onboard JUICE, whose main scientific goals are to understand ice tectonics based on topographic data, the subsurface structure by measuring tidal response, and small-scale roughness and albedo of the surface. In addition, from the perspective of astrobiology, it is imperative to study the subsurface ocean scientifically. The development of GALA has proceeded through an international collaboration between Germany (the lead), Japan, Switzerland, and Spain. Within this framework, the Japanese team (GALA-J) is responsible for developing three receiver modules: the Backend Optics (BEO), the Focal Plane Assembly (FPA), and the Analog Electronics Module (AEM). Like the German team, GALA-J also developed software to simulate the performance of the entire GALA system (performance model). In July 2020, the Proto-Flight Models of BEO, FPA, and AEM were delivered from Japan to Germany. This paper presents an overview of JUICE/GALA and its scientific objectives and describes the instrumentation, mainly focusing on Japan’s contribution

A 4.7-THz gas laser local oscillator for GREAT on SOFIA

A particularly important transition for astronomy is the OI fine structure line at 4.7 THz. It is an important cooling line of the interstellar medium and allows studying the chemical composition, the evolution, and the dynamical behavior of astronomical objects. Consequently, this transition is a main target to be observed with GREAT, the German Receiver for Astronomy at Terahertz Frequencies, which will be operated on board of SOFIA. A major challenge for a heterodyne receiver operating at such a high frequency is the local oscillator (LO). Despite significant progress in the development of a quantum-cascade laser based LO [1] the baseline design for GREAT is an optically pumped gas laser operated at 4.7 THz. In this report we will present the design and performance of the 4.7-THz gas laser LO for SOFIA. The LO is based on a radio frequency excited CO2 laser which has a sealed-off gas volume and which is frequency tunable by a grating. The CO2 laser is operated on the 9P12 transition of the CO2 molecule. The output emission is focused into the THz laser resonator. The THz laser is transversely excited. It operates on the 4.75 THz line of 13CH3OH. For frequency stabilization of the CO2 laser a small part of its output radiation is guided into a Fabry-Pérot interferometer (FPI) which serves as a length or frequency reference. In order to compensate for temperature or pressure induced drifts of the FPI length the emission of a frequency stabilized a helium-neon (HeNe) laser is coupled into the FPI as well. The FPI is locked to the emission of the HeNe laser. We will present the design and the performance of the LO with respect to output power, short and long term power stability, and beam profile. The system is ready and awaits implementation in GREAT and operation on board of SOFIA

QCL as 4.7 THz Local Oscillator for SOFIA

We report on the performance of a 4.7-THz local oscillator (LO) for the heterodyne spectrometer GREAT (German REceiver for Astronamy at Terahertz frequencies) on SOFIA (Stratospheric Observatory For Infrared Astronomy). The design of the LO and its performance in terms of output power, frequency accuracy, frequency stability, and beam profile as well as its implementation in GREAT will be presented

Performance of the 4.7-THz Local Oscillator with Quantum Cascade Laser on Board of SOFIA

— The design and the performance of a 4.7-THz local oscillator (LO) for the GREAT (German REceiver for Astronomy at Terahertz frequencies) heterodyne spectrometer on SOFIA, the Stratospheric Observatory for Infrared Astronomy, are presented. The LO is based on a quantum-cascade laser, which is mounted in a compact mechanical cryocooler. It delivers up to 150 µW output power into a nearly Gaussian shaped beam around the frequency of the fine structure line of neutral atomic oxygen, OI, at 4.7448 THz

4.7-THz Local Oscillator for SOFIA Based on a Quantum-Cascade Laser

Abstract— We report on the development of a 4.7-THz local oscillator (LO) for the heterodyne spectrometer GREAT on SOFIA. The design of the LO and its performance in terms of output power, frequency accuracy, frequency stability, and beam profile as well as its implementation in GREAT will be presented. I. INTRODUCTION H ETERODYNE spectroscopy of molecular rotational lines and atomic fine-structure lines is a powerful tool in astronomy and planetary research. It allows for the study of the chemical composition, the evolution, and the dynamical behaviour of astronomical objects such as molecular clouds and star-forming regions. For frequencies beyond 2 THz, SOFIA, the Stratospheric Observatory for Infrared Astronomy, is currently the only platform which allows for heterodyne spectroscopy at these frequencies. One example is the OI fine-structure line at 4.7448 THz, which is a main target to be observed with GREAT, the German Receiver for Astronomy at Terahertz Frequencies, on board of SOFIA. II. RESULTS The local oscillator (LO) combines a quantum-cascade laser (QCL) with a compact, low-input-power Stirling cooler. The 4.7-THz QCL is based on a hybrid design and has been developed for continuous-wave operation, high output powers, and low electrical pump powers [1]. Efficient carrier injection is achieved by resonant longitudinal optical phonon scattering. This design allows for an operating voltage below 6 V. The amount of generated heat complies with the cooling capacity of the Stirling cooler of 7 W at 65 K with 240 W of electrical input power [2]. The QCL has a lateral first-order distributed feedback (DFB) grating, which is optimized for 4.745 THz. This yields single-mode emission over most of the driving current of the laser. Outcoupling is achieved through one of the end facets of the single-plasmon waveguide. The beam of the QCL is shaped with a dedicated lens and a spatial filter into an almost Gaussian profile. The M2 value which can be achieved with this method is approximately 1.2 [3]. The peak output power of the QCL is 0.5 mW. Frequency stabilization is achieved by using a low-noise current source for the QCL and a dedicated temperature stabilization of the heat sink of the QCL. In this way, a frequency stability better than 1.6 MHz (full width at half maximum, FWHM) is achieved. This can be further reduced by locking the emission from the QCL to an absorption line of CH3OH at low pressures (approximately 1 hPa). Using a pyroelectric detector and a proportional-integral-derivative controller, an additional improvement of the frequency stability is achieved [4]. Using this scheme, the FWHM of the laser line is below 0.5 MHz within 30 minutes measurement time. The absolute frequency of the LO has been determined by measuring the absorption spectrum of CH3OH and comparing this with data from the literature. It has been found that the LO emits in a range of ±4 GHz around the OI line. III. SUMMARY We have developed an LO for the heterodyne spectrometer GREAT on board of SOFIA. The LO is based on a QCL with a lateral DFB grating and a single-plasmon waveguide. The LO provides up to 0.5 mW output power in an almost Gaussian beam with an M2 value of 1.2. Its frequency is tunable by current and temperature within approximately ±4 GHz around the OI line. The LO fulfills all requirements and will be operated on SOFIA in 2014 for the first time. REFERENCES [1]. L. Schrottke, M. Wienold, R. Sharma, X. Lü, K. Biermann, R. Hey, A. Tahraoui, H. Richter, H.-W. Hübers, and H. T. Grahn, “Quantum-cascade lasers as local oscillators for heterodyne spectrometers in the spectral range around 4.745 THz,” Semicond. Sci. Technol. vol. 28, 035011 (2013). [2]. H. Richter, M. Greiner-Bär, S. G. Pavlov, A. D. Semenov, M. Wienold, L. Schrottke, M. Giehler, R. Hey, H. T. Grahn, and H.-W. Hübers, “A compact, continuous-wave terahertz source based on a quantum-cascade laser and a miniature cryocooler,” Opt. Express vol. 18, pp. 1017710187 (2010). [3]. H. Richter, A. D. Semenov, S. G. Pavlov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, K. S. Il’in, M. Siegel, and H.-W. Hübers, “Terahertz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer in a pulse tube cooler”, Appl. Phys. Lett. vol. 93, 141108 (2010). [4]. H. Richter, S. G. Pavlov, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, and H.-W. Hübers, “Submegahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line”, Appl. Phys. Lett. vol. 96, 071112 (2010)

Inklusives Experimentieren im naturwissenschaftlichen Unterricht digital unterstützen

Stinken-Rösner L, Weidenhiller P, Nerdel C, Weck H, Kastaun M, Meier M. Inklusives Experimentieren im naturwissenschaftlichen Unterricht digital unterstützen. In: Ferencik-Lehmkuhl D, Huynh I, Laubmeister C, et al., eds. Inklusion digital! Chancen und Herausforderungen inklusiver Bildung im Kontext von Digitalisierung. Bad Heilbrunn: Julius Klinkhardt; 2023: 152-167.Die Entwicklung einer scientific literacy for all stellt die Zielsetzung eines inklu-siven naturwissenschaftlichen Unterrichts dar, in dem Lernende neben Fachin-halten auch fächerübergreifende Kompetenzen erwerben. Insbesondere der Prozess der naturwissenschaftlichen Erkenntnisgewinnung, der einhergeht mit dem Erwerb und der Anwendung naturwissenschaftstypischer Denk- und Ar-beitsweisen, eröffnet vielfältige Nutzungsmöglichkeiten für digitale Medien, um im Prozess immanente Barrieren zu minimieren. Ausgehend vom NinU-Schemawird das didaktische Wirkungsfeld digitaler Medien im inklusiven natuwissen-schaftlichen Unterricht mit Fokus auf das Experimentieren in diesem Beitrag theoretisch umrissen sowie Einstellungen und die resultierende Unterrichtspraxis von Lehrkräften innerhalb dieses Feldes dargestellt. Die Ergebnisse verschiedener Projekte zeigen, dass, obwohl der Einsatz digitaler Medien beim Experimentieren bereits Einzug in die naturwissenschaftliche Unterrichtspraxis gefunden hat, das Potenzial einiger Medien für eine inklusive Unterrichtsgestaltung bisher noch nicht ausgeschöpft bzw. beachtet wird. Beispiele hierfür sind die Nutzung von eBooks zur Verständnisunterstützung von Experimentieranleitungen sowie die Einbindung von Experimentiervideos, um die Planungs-, Durchführungs- und Auswertungsphase beim Experimentieren zu unterstütze

The Ganymede laser altimeter (GALA): key objectives, instrument design, and performance

The Ganymede Laser Altimeter (GALA) is one of the ten scientific instruments selected for the Jupiter Icy Moons Explorer (JUICE) mission currently implemented under responsibility of the European Space Agency (ESA). JUICE is scheduled for launch in mid 2022; arrival at Jupiter will be by end of 2029 with the nominal science mission—including close flybys at Ganymede, Europa, and Callisto and a Ganymede orbit phase—ending by mid 2033. GALA’s main objective is to obtain topographic data of the icy satellites of Jupiter: Europa, Ganymede, and Callisto. By measuring the diurnal tidal deformation of Ganymede, which crucially depends on the decoupling of the surface ice layer from the deep interior by a liquid water ocean, GALA will obtain evidence for (or against) a subsurface ocean in a 500 km orbit around the satellite and will provide constraints on Ganymede’s ice shell thickness. In combination with other instruments, it will characterize the morphology of surface units on Ganymede, Europa, and Callisto providing not only topography but also surface roughness and albedo (at 1064 nm) measurements. GALA is a single-beam laser altimeter operating with up to 50 Hz (nominal 30 Hz) shot frequency at a wavelength of 1064 nm and pulse lengths of 5.5±2.5 ns using a Nd:YAG laser. The return pulse is detected by an Avalanche Photo Diode (APD) with 100 MHz bandwidth and is digitized at a sampling rate of 200 MHz providing range measurements with a subsample resolution of 0.1 m and surface roughness measurements from pulse-shape analysis on the scale of the footprint size of about 50 m at 500 km altitude. The instrument is developed in collaboration of institutes and industry from Germany, Japan, Switzerland, and Spain