SC2 / ASTROPHOTONICS

The observations of the sky is deeply rooted in many cultures. Apart from quenching the thirst for knowledge, astronomy has always served practical purposes as well, e.g. as an indispensable tool for measuring time and determining positions. Modern astronomical observations tend to be oriented towards fundamental questions. Which laws of the nature governed the formation of the universe, the solar system, and the characteristics of the elementary particles? Is there any other life in the universe or are we alone, out there?

Improved astronomical observation possibilities allow deeper glances into the past of the entire cosmos. Knowledge gained serve as a test bench for physical theories under conditions far outside the reach of any experiment on earth. Simultaneously, understanding the internal dynamics of stars also has tangible implications for everyday life, since sudden activity fluctuations of the sun could potentially wreak havoc on today's global technological infrastructure.

The future development of astronomical observation facilities around the world is currently being planned in the framework of several challenging scientific programs. In Europe the activities of the ground based astronomy in the visible and near-infrared are coordinated by networks such as OPTICON and the European Southern Observatory (ESO). A common European position for strategy and priorities in astronomy is documented by Astronet [1, 2], a consortium of all important national funding agencies in Europe (i.a. BMBF).

High resolution spectroscopy from the optical to the infrared […] will allow unprec­edented progress in [the study of star and planet formation].

(Science with the E-ELT)

The Infrastructure Roadmap [1] documents the priorities for the planned observatories. One of the most ambitious projects currently under way is the realization of the "European Extremely Large Telescopes" (E-ELT) featuring a primary mirror diameter of nearly 40 m, a total budget of approximately €1bn., and a projected completion in 2024 [3]. Other currently planned large telescopes include the Giant Magellan Telescope (planned completion 2020) [4] and the Thirty Meter Telescope in Hawaii (planned completion 2022) [5]. These facilities will be equipped with a large number of scientific instruments that are expected to yield seminal progress in a number of fields [3]:

  • Exoplanets: The existence of planets outside our solar system has been confirmed for more than a decade. However, these objects have thus far eluded any direct observation. The new generation of telescopes will finally provide the necessary resolution, and enable search for signs of life.
  • Cosmology / Fundamental physics / Elementary particle physics: Current understanding of the evolution of our universe and the physical laws governing its dynamics is still far from complete. For example, neither the inflationary expansion nor the nature of dark matter and - energy and their influence on the largest structures are satisfactorily explained. New observatory capabilities will sharpen our gaze on the structure and properties of the universe. Focussing on long-standing questions such as hypothetical changes of the natural constants or the ultimate fate of the expanding universe.
  • Astrophysics / Formation of stars / Planet formation: The new generation of telescopes will dramatically increase the number of observable stars in our galaxy and, thus, will substantially increase the level of detail in our understanding of the formation of stars and planets. Furthermore, it will be elucidated if our own solar system represents an exception or if there are similar systems in the galaxy.

However, any boost in resolution and aperture of a telescope can only unfold its full potential if the performance of the subsequent instruments can be increased in kind. Core components of many observatories are highly sensitive and resolving spectrometers. This is illustrated by the ESO Instruments Summary Table which lists around 25 currently used spectroscopic instruments installed in different ESO telescopes [6]. The Astronet Infrastructure Roadmap [1] assigns the further development of this class of instruments the highest priority.

Even in the E-ELT Instrumentation Roadmap the spectroscopy is prominent represented: HARMONI, METIS, HIRES and ELT-MOS are four of the first planned spectrographs. The key components of these instruments are optical gratings for spectrally resolved measurements.

ENABLER: EFFICIENT, ULTRA-PRECISE SPECTROMETER GRATINGS

The enormous requirements for these astrophysical experiments will reflect in the specifications of the spectrometer gratings. It is of crucial importance to maximize their efficiency while maintaining high wavefront accuracy and minimizing any background due to scattered light. Moreover, astronomical applications routinely require exceptionally large gratings, e.g. >500 mm (e.g. HARPS instrument [7]). Often such components are realized in multiple segments that require highly precise joining.

Through the necessary development work competitiveness and innovative strength are increased.

(BMBF-Weltall: Einblicke in den Kosmos)

Depending on the task at hand, two classes of gratings may be employed:

  • High bandwidth at moderate spectral resolution : In this scenario, the typical choice is a so-called "blazed" grating, which features a continuously varying phase function within each grating period.
  • High spectral resolution at low bandwidth : can be achieved by employing binary nanostructured gratings at grazing incidence [8].

Abb. 1: Spektroskopisches Gitter für die Sentinel-4 Erdbeobachtungsmission. Nanooptische Gitter sind ein Schlüsselelement in der Instrumentierung von Weltraummissionen.
Abb. 1: A spectroscopic gratings for the Sentinel-4.

It illustrated the parameters for one of the five gratings in the currently planned MOONS instrument (Multi Object Optical and Near-infrared Spectrograph) for the Very Large Telescope (VLT) [9, 10].

Tab. 1: Technische Parameter des MOONS Spektrometergitters für das H-Band.
Tab. 1: Technical parameters of the MOONS spectrometer grating for the H band.

Currently three alternative approaches exist for the realization of gratings for ground based astronomic instrumentation:

  • Holographic volume gratings:: Gratings structures realized as refractive index modulations in photoresist [11].
  • Lithographic surface gratings: Dielectric surface gratings implemented by direct-inscription lithographic processes [12].
  • Lithographic volume gratings: Combinations of sealed, cavity free, subsurface gratings on optical active, non-planar substrates (so-called GRISM). They are realized by direct writing lithography, conformal depositing methods and high-precision optical joining technology [13, 14].

Ultra-stable spectrographs […] will achieve measure­ment precisions of ~1 cm/s […]. For the detection of rocky planets in habitable zones, this precision is needed […].

(Science with the E-ELT)

The advantages of lithographic methods are based on the superior level of control over the nanoscopic grating structure, and the corresponding higher flexibility of optical parameters. Setting it apart from any other fabrication technique, electron beam lithography allows for a well-defined tuning of the nanostructures to deliver customized features such as polarization dependence or spectral behavior.

In principle, direct-inscription methods are virtually arbitrarily scalable to large areas, while maintaining an excellent degree of homogeneity across the entire grating area [12] rather easier practicable than holographic exposure techniques.

Based on the discussed scalability and its strong competence in nanostructure technology, coating and integration techniques, NPL will focus on lithographic gratings. Those will be scaled to the necessary parameters together with the end user.

Abb. 2: Nanostruktur des GAIA-Gitters. Nur durch innovative Strukturierungskonzepte konnten die Ziele der ESA erreicht werden.
Abb. 2: Nanostructure of the GAIA-grating/grid. The objectives of the ESA could be achieved only through innovative structuring concepts.

SCIENTIFIC-TECHNOLOGICAL IMPLEMENTATION

In order to support gratings larger than 500 mm in diameter, massive substrates with a weight of 50 kg or more will be necessary. This requires the development of customized handling procedures and processes for cleaning as well as resist coating to ensure the excellent quality of the final nanostructures.

Astrophysics is considered as declared technology driver, especially in the range of optic technologies.

(BMBF - Weltall: Einblicke in den Kosmos)

Along these lines, the main technological challenges are:

  • Electron beam lithography or scanning-beam interference lithography as well as etching- and coating procedures for substrates exceeding diameters of 500 mm and masses of 30 kg.
  • High-resolution characterization techniques for sub-micrometer structures (scanning electron microscopy, atomic force microscopy) on large-area substrates.

The long-standing expertise of the Fraunhofer IOF is attested by the successful completion of numerous projects in related fields [12, 15, 16], as well as close ties with development activities, and internationally recognized capabilities in large-area nanostructured components [17, 18]. Required processing facilities, technologies and measurement methods will be developed in close collaboration with end users and industrial partners.

Abb. 3: Realized grating during efficiency measurement, grating size: 250mm x 130mm
Abb. 3: Realized grating during efficiency measurement, grating size: 250mm x 130mm.

INVESTMENT REQUIREMENTS

To meet the abovementioned requirements the following investments for the core technologies are necessary.

IMPORTANT PROJECTS OF THE NPL-PARTNERS

  • Metrology for Aspheres at Mahr Gmbh in cooperation with Institut für Technische Optik Stuttgart.
  • X-ray silicon pore optics for ATHENA (Advanced Telescope for High-ENergy Astrophysics) at European Space Agency (ESA) link
  • RVS Fiber Laser for ATV 5 at International Space Station (ISS) in cooperation with JenaOptronik, European Space Agency (ESA) link
  • NIR-Spectrometer Grating for CarbonSat at European Space Agency (ESA) in cooperation with Thales Alenia Space link
  • SWIR Grism for CarbonSat at European Space Agency (ESA) in cooperation with Thales Alenia Space link
  • Black Bodies (BB) for IRS and FCI Instruments for COM at European Space Agency (ESA) in cooperation with MICOS, ABB-Canada.
  • Order Sorter Filters for CRIRES+ at Very Large Telescope (VLT) in cooperation with Thüringer Landessternwarte Tautenburg, European Southern Observatory (ESO) link
  • UV-Spectrometer Grating for CUBES at Very Large Telescope (VLT) in cooperation with European Southern Observatory (ESO) link
  • Computer Generated Hologramm for Wavefront Calibration for CUBES at Very Large Telescope (VLT) in cooperation with European Southern Observatory (ESO) link
  • Phase shifter for DARWIN at Max-Planck-Institut für Astrophysik (MPIA) in cooperation with Max-Planck-Institut für Astrophysik (MPIA) link
  • Computer Generated Hologramm for Wavefront Calibration for DESIS at Deutsches Zentrum für Luft und Raumfahrt (DLR) link
  • Prisms for EnMAP at Deutsches Zentrum für Luft und Raumfahrt (DLR) in cooperation with OHB link
  • Micromirros for EnMAP at Deutsches Zentrum für Luft und Raumfahrt (DLR) in cooperation with OHB link
  • Computer Generated Hologramm for Wavefront Calibration for EnMAP at Deutsches Zentrum für Luft und Raumfahrt (DLR) in cooperation with OHB link
  • Mirros for EnMAP at Deutsches Zentrum für Luft und Raumfahrt (DLR) in cooperation with OHB link
  • Extreme Adaptive Optics (XAO) for EPICS at European Extremely Large Telescope (E-ELT) in cooperation with European Southern Observatory (ESO) link
  • Green Laser for ExoMars at European Space Agency (ESA) in cooperation with INTA, Monocrom link
  • Cold Mirror Set for FIAT at European Extremely Large Telescope (E-ELT) in cooperation with European Southern Observatory (ESO) link
  • Spectrometer Gratings for FLEX/FLORIS at European Space Agency (ESA) in cooperation with Astrium DS link
  • Effective-Index Spectrometer Grating for GAIA at European Space Agency (ESA) in cooperation with Astrium DS link
  • Computer Generated Hologramm for Wavefront Calibration for GAIA at European Space Agency (ESA) in cooperation with Sagem link
  • Fiber Collimator for GRACE-FO at National Aeronautics and Space Administration (NASA) in cooperation with Deutsches Zentrum für Luft und Raumfahrt (DLR) (Spacetech), European Space Agency (ESA) link
  • Derotator Mirror Unit for GRAVITY at Very Large Telescope (VLT) in cooperation with Max-Planck-Institut für Astrophysik (MPIA), European Southern Observatory (ESO) link
  • Foster Prism for HIRES at European Extremely Large Telescope (E-ELT) in cooperation with European Southern Observatory (ESO), Leibniz-Institut für Astronomyphysik Potsdam (AIP) link
  • Retarder for HIRES at European Extremely Large Telescope (E-ELT) in cooperation with European Southern Observatory (ESO), Leibniz-Institut für Astronomyphysik Potsdam (AIP) link
  • Polarisation Optics for HIRES at European Extremely Large Telescope (E-ELT) in cooperation with European Southern Observatory (ESO), Leibniz-Institut für Astronomyphysik Potsdam (AIP) link
  • High Energy Fiber Laser for InnoSpace at Deutsches Zentrum für Luft und Raumfahrt (DLR) link
  • Solar Auto-Calibrating Extreme UV/UV Spectrophotometers (SOL-ACES) for International Space Station (ISS) at Deutsches Zentrum für Luft- und Raumfahrt (DLR) in cooperation with Fraunhofer IPM Freiburg link
  • NIRSpec Instrument Metrology for James Webb Space Telescope at European Space Agency (ESA) in cooperation with EADS Astrium link
  • Material Samples for James Webb Space Telescope at European Space Agency (ESA) link
  • Piston Mirror for LINC-NIRVANA at Large Binocular Telescope (LBT) in cooperation with Max-Planck-Institut für Astrophysik (MPIA) link
  • Fiber Laser for LiQuaRD at Deutsches Zentrum für Luft und Raumfahrt (DLR) in cooperation with JenaOptronik link
  • Mirror Components for LUCIFER at Large Binocular Telescope (LBT) in cooperation with Max-Planck-Institut für Astrophysik (MPIA) link
  • Spectrometer Optics for MERTIS at European Space Agency (ESA) in cooperation with OHB, Deutsches Zentrum für Luft und Raumfahrt (DLR), Jaxa link
  • Computer Generated Hologramm for Wavefront Calibration for METimage at Deutsches Zentrum für Luft und Raumfahrt (DLR) in cooperation with JenaOptronik link
  • TMA-Telescope Optics for METimage at Deutsches Zentrum für Luft und Raumfahrt (DLR) in cooperation with JenaOptronik link
  • Imager Optical Components for METIS at European Extremely Large Telescope (E-ELT) in cooperation with Max-Planck-Institut für Astrophysik (MPIA), European Southern Observatory (ESO) link
  • Camera Optics for MICADO at European Extremely Large Telescope (E-ELT) in cooperation with Max-Planck-Institut für extraterrestrische Physik (MPI MPE), European Southern Observatory (ESO) link
  • Test Masses for Microscope Satelite Mission at European Space Agency (ESA) in cooperation with Onera, ZARM, CNRS link
  • Main Optics Mirror Spectrometer for MIRI at James Webb-Telescope in cooperation with AstronomyN, Netherlands Consortium link
  • Spectrometer Optics for MUSES, DESIS at International Space Station (ISS) in cooperation with Deutsches Zentrum für Luft und Raumfahrt (DLR) link
  • X-Ray Zone Lens for Panter X-ray test facility at Max-Planck-Institut für extraterrestrische Physik (MPI MPE) in cooperation with Max-Planck-Institut für extraterrestrische Physik (MPI MPE) link
  • Three-Mirror-Anastigmat for PCW at Canadian Space Agency (CSA) in cooperation with ABB-Canada link
  • Image Slicer for PEPSI at Large Binocular Telescope (LBT) in cooperation with Leibniz-Institut für Astronomyphysik Potsdam (AIP) link
  • TMA-telecope opics for PREMIER at European Space Agency (ESA) in cooperation with Airbus link
  • TMA-Telescope Optics for Rapid Eye at Deutsches Zentrum für Luft und Raumfahrt (DLR) in cooperation with JenaOptronik, Rapid Eye AG link
  • Filter Assemblies for Sentinel-2 at European Space Agency (ESA) in cooperation with JenaOptronik link
  • UVN objective for Sentinel-4 at European Space Agency (ESA) in cooperation with Astrium DS link
  • NIR-Spectrometer Grating for Sentinel-5 at European Space Agency (ESA) in cooperation with JenaOptronik link
  • Spectral Imaging of the Coronal Environment (SPICE instrument) for Solar Orbiter at European Space Agency (ESA) in cooperation with Max-Planck-Institut für Sonnensystemforschung (MPS) link
  • Extreme Ultraviolet Imager (EUI) for Solar Orbiter at European Space Agency (ESA) in cooperation with Centre spatial de Liège (CSL) link
  • Material samples for Space Infrared Telescope for Cosmology and Astrophysics (SPICA) at European Space Agency (ESA) link
  • Autofocus System for StarTiger at European Space Agency (ESA) link
  • Active Optics for STOIC at European Space Agency (ESA) in cooperation with National University of Ireland Galway, European Space Agency (ESA).
  • Adaptive Optics for transportable feeder links at Deutsches Zentrum für Luft und Raumfahrt (DLR).
  • Computer Generated Hologramm for Wavefront Calibration for VISTEL at Deutsches Zentrum für Luft und Raumfahrt (DLR).


LITERATURE

[1] M. F. Bode, M. J. Cruz, and F. J. Molster. The ASTRONET Infrastructure Roadmap: A Strategic Plan for European Astronomy. ASTRONET (2008).

[2] P. T. de Zeeuw and F. J. Molster, eds. A Science Vision for European Astronomy. ASTRONET (2010).

[3] E-ELT Science Office. An expanded view of the universe - science with the European extremely large telescope (2011).

[4] GMTO Corporation. Giant magellan telescope - scientific promise and opportunities (2012).

[5] W. Skidmore, ed. Thirty Meter Telescope - Detailed Science Case. TMT Observatory Corporation (2015).

[6] Eso instruments summary table.

[7] ESO. HARPS User Manual 2.1 (2011).

[8] T. Clausnitzer, T. Kämpfe, E.-B. Kley et al. Highly-dispersive dielectric transmission gratings with 100% diffraction efficiency. Opt. Express, 16:5577 (2008). doi: 10.1364/OE.16.005577.

[9] E. Oliva, E. Diolaiti, B. Garilli et al. The design of the moons-vlt spectrometer. Proc. SPIE, 8446:84464V (2012). doi: 10.1117/12.925309.

[10] E. Oliva, S. Todd, M. Cirasuolo et al. Updated optical design and trade-off study for moons, the multi-object optical and near infrared spectrometer for the vlt. Proc. SPIE, 9147:91472C (2014). doi: 10.1117/12.2054425.

[11] J.-K. Rhee, J. A. Arns, W. S. Colburn et al. Chirped-pulse amplification of 85-fs pulses at 250 khz with third-order dispersion compensation by use of holographic transmission gratings. Opt. Lett., 19:1550 (1994). doi: 10.1364/OL.19.001550.

[12] U. Zeitner, M. Oliva, F. Fuchs et al. High performance diffraction gratings made by e-beam lithography. Appl. Phys. A, 109:789 (2012). doi: 10.1007/s00339-012-7346-z.

[13] G. Kalkowski, G. Harnisch, K. Grabowski et al. Low temperature grism direct bonding. Proc. SPIE, 9574:95740K (2015). doi: 10.1117/12.2187241.

[14] T. Paul, A. Matthes, T. Harzendorf et al. Half-wave phase retarder working in transmission around 630nm realized by atomic layer deposition of sub-wavelength gratings. Opt. Mater. Express, 5:124 (2015). doi: 10.1364/OME.5.000124.

[15] M. Erdmann, E.-B. Kley, and U. Zeitner. Development of a large blazed transmission grating for the gaia radial velocity spectrometer. In International Conference on Space Optics (2010).

[16] U. D. Zeitner, F. Fuchs, and E.-B. Kley. High-performance dielectric diffraction gratings for space applications. Proc. SPIE, 8450:84502Z (2012). doi: 10.1117/12.928286.

[17] S. Scheiding, M. Beier, U.-D. Zeitner et al. Freeform mirror fabrication and metrology using a high performance test cgh and advanced alignment features. Proc. SPIE, 8613:86130J (2013). doi: 10.1117/12.2001690.

[18] S. Schröder, T. Herffurth, H. Blaschke et al. Angle-resolved scattering: an effective method for characterizing thin-film coatings. Appl. Opt., 50:C164 (2011). doi: 10.1364/AO.50.00C164.

Astrooptik
Astrooptik

USER

Astronomic Observation

SCIENTIFIC FIELDS

- Exoplanets
- Cosmology
- Fundamental Physics
- Elementary Particle Physics
- Astrophysics
- Star Formation
- Protoplanetary Systems

ENABLER

- Great, Highly precise Spectrometer Gratings of high Efficiency

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Logo Fraunhofer IOF
Logo Deutsches Elektronen-Synchrotron
Logo GSI Helmholtzzentrum für Schwerionenforschung
Logo Physikalisch-Technische Bundesanstalt
Logo Fraunhofer IOF Logo Deutsches Elektronen-Synchrotron Logo GSI Helmholtzzentrum für Schwerionenforschung Logo Physikalisch-Technische Bundesanstalt