Universität zu Köln

Erste Beobachtungen mit dem abstimmbaren Infrarot-Heterodynsystem THIS

Wirtz, Daniel (2005) Erste Beobachtungen mit dem abstimmbaren Infrarot-Heterodynsystem THIS. PhD thesis, Universität zu Köln.

[img]
Preview
PDF
Download (12Mb) | Preview

    Abstract

    Gegenstand der vorliegenden Arbeit ist die technische Weiterentwicklung des durchstimmbaren Infrarot-Heterodynsystems THIS (Tuneable Heterodyne Infrared Spectrometer) sowie die Planung, Vorbereitung und Durchführung diverser Beobachtungseinsätze des Instruments an unterschiedlichen Teleskopen. Auf technischer Seite konnte der sehr erfolgreiche Einsatz von Quanten- Kaskadenlasern als Lokaloszillatoren, die Empfindlichkeit des Systems erstmals auf das Niveau von CO2-Laser gepumpten Instrumenten bringen. Frequenzstabilität und radiometrisches Verhalten des Instruments konnten für Beobachtungszeiträume von einigen Stunden nachgewiesen werden.Weiterhin wurde ein in den Empfänger integriertes, optisches Guide-System für den Einsatz an Teleskopen entwickelt und aufgebaut. Die neu entwickelte Optik macht THIS durch die Verwendung einer integrierten optischen Kamera sowie eines Scannerspiegels zur Auswahl von Beobachtungspositionen am Himmel weitgehend unabhängig vom Teleskoptyp und damit vielseitig einsetzbar. Die technischen Neuerungen und die mechanische Stabilität des neuen Aufbaus wurden u. a. während Messperioden am Observatorium Hoher List bei Daun/Eifel sowie am McMath-Pierce Solar Telescope auf dem Kitt Peak nahe Tucson/Arizona erstmalig außerhalb des Labors genutzt und getestet. Es konnten Molekül-Absorptionen aus Sonnenflecken aufgenommen und aus den vollständig aufgelösten Linienprofilen die Anregungstemperaturen des Materials bestimmt werden. In diesem Zusammenhang wurde eine theoretische Analyse der Kalibration von am Teleskop gewonnenen Spektren durchgeführt und auf die gemessenen Daten angewandt. Weiterhin konnten erstmals mit THIS nicht-terrestrische Signale in Form von schwachen, nicht-thermischen CO2- Emissionen aus der von der Sonne beleuchteten Venus- und Mars-Atmosphäre detektiert werden. Die exzellente Empfindlichkeit des Instruments konnte zusätzlich durch die Beobachtung von stratosphärischem Ozon gegen einen Stern als Hintergrundquelle demonstriert werden. Weitere Beobachtungseinsätze von THIS sind in Zusammenarbeit mit dem GSFC der NASA in Vorbereitung. Beobachtungsziele sind interessante molekulare Absorptions- und Emissionslinien in Planetenatmosphären, die nicht mit Gaslaser-Instrumenten beobachtbar sind. Dazu zählt die hochaufgelöste Vermessung der bereits erwähnten CO2-Laseremissionen oder die Bestimmung von Häufigkeiten von leichten Kohlenwasserstoffen wie C2H4 oder C2H6.

    Item Type: Thesis (PhD thesis)
    Translated abstract:
    AbstractLanguage
    The ongoing technical development of the Cologne Tuneable Heterodyne Infrared Spectrometer THIS as well as the planning, preparation and execution of various observing runs at different telescopes is the topic of this thesis. One goal was the gathering of valuable spectroscopic data in order to demonstrate the competitiveness of the system as a whole. The second goal was further preparation of THIS for future observing runs aboard the Stratospheric Observatory For Infrared Astronomy SOFIA and possible interferometric applications. This thesis deals with two main technical aspects. With the very successful implementation of quantum cascade lasers as local oscillators the sensitivity of THIS reached the quality of CO2-laser pumped systems for the first time. In the lab as well as during telescope operation system noise temperatures well below 4000K were reached. Combined with the frequency-stability and radiometric behavior (see chapter 5 and also [Son02]) a competitive tuneable IR-heterodyne receiver for astronomical applications is available for the first time. An optical guide-system for telescope use was also implemented in the receiver. This also includes a scanner mirror for beam-switching. The newly developed optical unit turned out to be necessary since an appropriate optical control of the field of view which is fundamental for proper guiding is not available at most telescopes. Moreover only few telescopes are equipped with a wobbling secondary mirror which allows beam-switching on the sky. Thus the new guide-system allows THIS to be used on all kinds of telescopes and provides much more independency. In collaboration with the Fraunhofer-Institut für Angewandte Festkörperphysik (IAF) in Freiburg newly developed Quantum Well Infrared Photodetectors (QWIPs) were successfully tested for the first time in our heterodyne system. The system noise temperatures reached were still a factor of 10 off the quantum-limit but improvements are on the way and QWIPs promise to offer several GHz of instantaneous bandwidth with is highly desireable especially for atmospheric applications. The technical advances have been tested outside the lab during observing runs at the 1 m-telescope at Hoher List observatory1 and two times two weeks runs at the McMath-Pierce Solar Telescope2 at Kitt Peak near Tucson/Arizona. First of all the mechanical stability of the system could be reproduced at Hoher List observatory because the receiver was mounted to the Cassegrain-focus of the telescope: down to elevation angles of 15 the system operated with stable LO-frequency. During this run the atmospheric transmission was studied (Sky-Dips were carried out) and stratospheric trace gas absorptions were detected. After this preparation a non-terrestrial signal was detected with THIS for the first time. A weak non-thermal CO2-emission from the illuminated Venus-atmosphere was recorded. Moreover molecular absorptions from sunspots were detected during this run and the fully resolved lineshapes allowed the determination of excitation temperatures of the material. In this context a theoretical analysis of the calibration of measured spectra was carried out and applied to the data gained. In 2003 the effort focussed on measuring high-resolution spectra of ozone-absorptions at different points in the Martian atmosphere. In collaboration with the NASAGoddard Space Flight Center GSFC in Greenbelt/ Maryland these data are currently reduced and used for studying atmospheric-chemistry phenomena on Mars. As a byproduct, the weak non-LTE emission-core of the CO2-P(30)-laser-line was also detected. Further high-resolution measurements of this kind using THIS might help exploiting the natural laser mechanism in both Martian and Venusian atmospheres for gainig insight into atmospheric variability. Moreover the excellent performance of the instrument and the good coupling to the telescope could be demonstrated by measuring stratospheric ozoneabsorptions against a star as a weak background source. Since both Kitt Peak runs were very promising follow-up runs of THIS are planned in collaboration with the NASA GSFC. Interesting targets will be molecular absorption- and emission-lines in planetary atmospheres that can not be detected using fixed-frequency CO2-lasers as LO. This includes non-LTE phenomena as well as the determination of abundances of hydrocarbons like C2H4 or C2H6.English
    Creators:
    CreatorsEmail
    Wirtz, Danieldwirtz@web.de
    URN: urn:nbn:de:hbz:38-14473
    Subjects: Physics
    Uncontrolled Keywords:
    KeywordsLanguage
    Heterodyn, Spektrometer, Infrarot, Quanten-Kaskaden Laser, LokaloszillatorGerman
    heterodyne, infrared, spectrometer, quantum-cascade laser, local oscillatorEnglish
    Faculty: Mathematisch-Naturwissenschaftliche Fakultät
    Divisions: Mathematisch-Naturwissenschaftliche Fakultät > I. Physikalisches Institut
    Language: German
    Date: 2005
    Date Type: Completion
    Date of oral exam: 08 February 2005
    Full Text Status: Public
    Date Deposited: 31 May 2005 09:19:04
    Referee
    NameAcademic Title
    Schieder, RudolfProf. Dr.
    URI: http://kups.ub.uni-koeln.de/id/eprint/1447

    Actions (login required)

    View Item