A study of the performance of a nulling interferometer testbed preparatory to the Darwin mission Pavel Gabor To cite this version: Pavel Gabor. A study of the performance of a nulling interferometer testbed preparatory to the Darwin mission. Astrophysics [astro-ph]. Université Paris Sud - Paris XI, 2009. English. tel-00439669 HAL Id: tel-00439669 https://tel.archives-ouvertes.fr/tel-00439669 Submitted on 8 Dec 2009 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Ecole´ Doctorale d’Astronomie et d’Astrophysique d’Ile-de-Franceˆ THESE` present´ ee´ pour obtenir le grade de DOCTEUR DE L’UNIVERSITE´ DE PARIS XI specialit´ e´ : ASTROPHYSIQUE par PAVEL GABOR ETUDE´ DES PERFORMANCES D’UN BANC INTERFEROM´ ETRIQUE´ EN FRANGE NOIRE DANS LE CADRE DE LA PREPARATION´ DE LA MISSION DARWIN Soutenue publiquement le 22 septembre 2009 devant le jury : Jean-Pierre Bibring, President´ Peter Lawson, Rapporteur Franc¸ois Reynaud, Rapporteur Jonathan Lunine, Examinateur Daniel Rouan, Examinateur Alain Leger,´ Directeur de these` Contents Preface vii 0.1 Teamwork ........................................... vii 0.2 Initiation ............................................ vii 0.3 Work in a team: my acknowledgments ............................ viii 0.4 Goals and objectives ..................................... viii 0.5 Organisation of the dissertation ................................ ix 1 Astrobiology and Exoplanetology 1 1.1 Are we alone? ......................................... 1 1.1.1 What is life? ..................................... 1 1.1.2 Current scientific approaches ............................. 4 1.2 Exoplanets ........................................... 5 1.2.1 Indirect detection ................................... 6 1.2.2 Direct observation .................................. 7 1.2.3 Step by step ...................................... 9 1.3 Formation-flying nulling interferometer ........................... 9 1.3.1 Design overview ................................... 10 1.3.2 Nulling ratio ..................................... 11 1.3.3 Stability ........................................ 13 2 Nulling Interferometry 15 2.1 Bracewell’s principle ..................................... 15 2.2 Performance parameters ................................... 16 2.3 Achromatic Phase Shifters .................................. 18 2.4 The Dispersive Prisms APS .................................. 20 2.5 Wavefront filtering ...................................... 20 2.6 Stability ............................................ 22 2.7 State of the art ........................................ 23 ii CONTENTS 3 Description of S & N 27 3.1 Introduction .......................................... 28 3.1.1 The purpose of this Chapter ............................. 28 3.1.2 General note ..................................... 28 3.1.3 Historical background ................................ 29 3.2 General overview ....................................... 32 3.2.1 An outline ...................................... 32 3.2.2 General layout .................................... 33 3.3 Purpose of the subsystems .................................. 36 3.3.1 A point source observed by two apertures ...................... 36 3.3.2 Three remarks on single-mode fibres ......................... 36 3.3.3 Off-axis parabolic mirrors .............................. 37 3.3.4 Symmetry ....................................... 38 3.3.5 Flux balancing .................................... 40 3.3.6 Stability ........................................ 41 3.3.7 Optical path ...................................... 43 3.4 Sources ............................................ 44 3.4.1 Ceramic black body ................................. 44 3.4.2 3.39 µm HeNe laser ................................. 46 3.4.3 Supercontinuum laser source ............................. 46 3.4.4 2.32 µm laser diode .................................. 47 3.5 Modal filters .......................................... 48 3.5.1 Fluoride-Glass Single-Mode Fibres ......................... 48 3.5.2 Fibre output aperturing ................................ 48 3.6 Spectral filters ......................................... 48 3.7 Polarisers ........................................... 50 3.8 Detectors ........................................... 50 3.8.1 Array detector .................................... 50 3.8.2 Single element detector ................................ 50 3.9 Phase shifter prototypes .................................... 53 3.9.1 Focus Crossing or Through Focus .......................... 53 3.9.2 Field Reversal or Periscope .............................. 53 3.9.3 Dispersive prisms ................................... 54 3.10 Electronics & Software .................................... 54 3.10.1 Lock-in amplifier ................................... 55 3.10.2 Software ....................................... 56 3.11 S ............................................ 60 3.12 S II ........................................... 63 CONTENTS iii 3.13 N .......................................... 64 4 Stabilisation 67 4.1 Introduction .......................................... 67 4.2 Metrology ........................................... 68 4.2.1 Setup and operation .................................. 68 4.2.2 Results ........................................ 68 4.3 Optical Path Difference Dithering .............................. 68 4.3.1 Introduction ...................................... 68 4.3.2 Principle ....................................... 70 4.3.3 Cycle parameters ................................... 70 4.4 Results ............................................. 72 4.4.1 K band ........................................ 72 4.4.2 Laser light ...................................... 75 4.5 Comparison with some other experiments .......................... 77 4.6 Discussion ........................................... 77 5 S results update 81 5.1 Preliminaries ......................................... 82 5.1.1 Thermal and mechanical instability ......................... 82 5.1.2 Detector calibration .................................. 82 5.1.3 Transmission ..................................... 82 5.2 Techniques .......................................... 83 5.2.1 Zero optical path difference and the CaF2 Prisms .................. 83 5.2.2 Fringe dispersion ................................... 83 5.2.3 Fourier transform ................................... 84 5.2.4 Direct nulling measurements ............................. 84 5.2.5 Experimental protocol ................................ 84 5.3 Nulling levels reached with S ............................. 85 5.3.1 The 2000 K black body ................................ 86 5.3.2 First effective stabilisation .............................. 86 5.3.3 3.39 µm HeNe laser and polarisers .......................... 86 5.3.4 S II: Improved mechanics and alignment ................... 89 5.3.5 Supercontinuum source ................................ 89 5.3.6 Focus crossing APS ................................. 89 5.3.7 Narrow band centred at 2.3 µm ............................ 90 5.3.8 Fibre curvature .................................... 90 5.3.9 L band ........................................ 90 5.4 Summary ........................................... 91 iv CONTENTS 6 Error budget 93 6.1 Tests and models ....................................... 93 6.1.1 Detector nonlinearity ................................. 93 6.1.2 Beam path ...................................... 94 6.1.3 Polarisation ...................................... 94 6.1.4 Chromatic shear and other dispersive effects ..................... 96 6.1.5 CaF2 Prisms: multiple working points ........................ 98 6.1.6 Coatings ....................................... 99 6.1.7 Inhomogeneities ................................... 99 6.1.8 Spectral mismatch .................................. 101 6.1.9 Wavefront quality ................................... 101 6.2 Testing on N ..................................... 102 6.3 Error budget .......................................... 102 6.4 Summary ........................................... 104 7 Conclusions and perspectives 105 7.1 What was to be done ..................................... 105 7.2 What was done ........................................ 106 7.2.1 My contribution ................................... 106 7.3 Perspectives .......................................... 107 7.3.1 N ...................................... 107 7.3.2 Polarisation ...................................... 107 7.3.3 Tests of achromatic phase shifters .......................... 107 7.3.4 Flux-balance stabilisation .............................. 108 7.3.5 Experiments around 10 µm .............................. 108 7.4 Towards a flagship space mission ............................... 108 7.5 Summary ........................................... 109 Appendices 111 A Cosmic Pluralism 113 A.1 Millennia of speculation ................................... 113 A.2 Links and implications .................................... 113 A.3 Historical notes ........................................ 114