LCM LNE-CNAM (Laboratoire Commun de Métrologie LNE-CNAM) Mesures hectométriques par interférométrie à longueur d’onde synthétique Journées Télémétrie Laser 20 & 21 octobre 2011 Observatoire de la Côte d’azur, Nice.2011 Sheherazade Azouigui, Thomas Badr, Patrick Juncar, Marc Himbert, Jean-Pierre Wallerand LCM LNE-CNAM (Laboratoire Commun de Métrologie LNE-CNAM)

OUTLINE Cadre de ce travail Principe de l’interférométrie à longueur d’onde synthétique et montage Comparaison en extérieur au FGI (Nummela, Finland) (v1 version) Validation en intérieur au VSL (Delft, Netherlands) (v2 version) Comparaison en extérieur au BEV (Innsbruck, Austria) (v2 version) Conclusions et suite

EMRP-JRP « Long distance » FRAMEWORK OF THE WORK EURAMET EMRP-JRP « Long distance » Aim: improve state of the art in distance measurement in air L / L  10-7 10-6/K RH 4% Synthetic wavelength Beat frequency Pulse pulse interferometry Spectroscopy Effective air index measurement Optical phase shift measurement Dispersion This work was carried out in the more general framework of the european metrology research program. More precisely it was a part of a joint research project (JRP) called long distance that finished last June of which I was the coordinator. The project had the ambition to improve the current state of the art in the measurement of distance in air, the target (quite challenging) was a relative uncertainty of 10-7 over 1 km. The basic idea to improve these measurements was to Distance measurement

Two-wavelength interferometry S M2 1 D 2

Signaux à f1 & f2 : 2 interféromètres hétérodynes THE SETUP OPTICAL SETUP LASER HEAD Signaux à f1 & f2 : 2 interféromètres hétérodynes Après élévation au carré: signal à f1-f2 Interféromètre superhétérodyne MEASUREMENT HEAD (20 GHz)

SYSTEME D’ACQUISITION f3=119.99 MHz

LE TELEMETRE

Nummela Standard Baseline – September 2010 OUTDOOR COMPARISON AT NUMMELA BASELINE Nummela Standard Baseline – September 2010 6 benchmark bolts in underground concrete pillars at 0, 24, 72, 216, 432 and 864 m (± 0.08 mm)

Fringe interpolation ~ 2p/1000 @ T=1 s ~ 2p/5000 @ T=60 s RESOLUTION OF THE SYSTEM ~ 5 µm @T=1 s D ~ 50 m SW ~ 7.5 mm ~ 2 µm @T=10 s ~ 0.7 µm @T=60 s Fringe interpolation ~ 2p/1000 @ T=1 s ~ 2p/5000 @ T=60 s

VSL – April 2011 Agreement ~5-10 mm INDOOR COMPARISON Displacement bench of 50 m but only 25 m available Using a classical optical system (fringe counting) as the reference system Spindler & Hoyer, He-Ne laser-based interferometer Agreement ~5-10 mm

BEV BASELINE – MAY 2011 OUTDOOR COMPARISON AT BEV BASELINE Difficult location close to the motorway Very busy traffic Very sunny days  Measurements only possible during 3 evenings

BEV BASELINE – MAY 2011 OUTDOOR COMPARISON AT BEV BASELINE Pillar 3 – Pillar 1 : D=120.03612 ±0.21mm (FGI – Sept. 2008) Reproducibility without touching the tribrack and level: ~20µm Reproducibility with only moving the holder on the tribrack : ~25 µm Reproducibility with moving the tribrack, centring and levelling adjustment: ~180 µm No possibility to state the accuracy at better than 210 µm

Distancemeter with micrometer resolution CONCLUSION Distancemeter with micrometer resolution Accuracy better than 10 µm (could be improved by considering electronic crosstalk) Outdoor with quiet environment, demonstration of measurements over 864 m Reproducibility of 20 µm demonstrated over 120 m Difficult to use with « very » perturbated atmosphere Still limited by temperature measurement for long distances (target uncertainty not reach) Possibility to include dispersion temperature measurements with YAG lasers (PTB already demonstrated over 100 m) “Transportable distance measurement system based on superheterodyne interferometry using two phase-locked frequency-doubled Nd:YAG lasers”, S. Azouigui,T. Badr, J.-P. Wallerand, M. Himbert, J. Salgado and P. Juncar REVIEW OF SCIENTIFIC INSTRUMENTS 81, 053112 (2010) “Transportable Distance Measurement System for Long-Range Applications”, Shéhérazade Azouigui, Thomas Badr, Jean-Pierre Wallerand, Marc Himbert, José-Antonio Salgado, Jean-Paul Senelaer, Frédéric Kwasnik, and Patrick Juncar IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 60, NO. 7, JULY 2011

Premier résultat résolution 0.02° sur ~500 ms. (~1µm pour 10 GHz) EN COURS Mise en place d’un système de mesure de déphasage du battement entre les deux lasers verts: 10 GHz Tête laser 10 GHz 10 GHz RF meas LO 10 GHz+50 kHz 50 kHz ref DAQ PC Idem pour PDref 50 kHz Premier résultat résolution 0.02° sur ~500 ms. (~1µm pour 10 GHz)

Compensation partielle de l’indice de l’air: A FAIRE RAPIDEMENT Compensation partielle de l’indice de l’air: Mesure de température par mesure de distance L à 2 longueurs d’onde (532 nm et 1064 nm) Ln1 = L01 Ln2 = L02 Pour de l’air sec, on montre que: L = L01 − A(L02 − L01) (A fonction uniquement de l01 et l02) Pour de l’air humide, on a une relation plus complexe qui suppose une mesure de l’humidité (et du taux de CO2) Déjà démontré jusqu’à 100 m par longueur d’onde synthétique (PTB, Allemagne) “Refractive index determination in length measurement by two-colour interferometry”, Karl Meiners-Hagen and Ahmed Abou-Zeid, Meas. Sci. Technol. 19 (2008) 084004 (5pp)

Merci de votre attention This research was in part funded by the European Community’s Seventh Framework Programme ERA-NET Plus, under grant agreement 217257. The research was performed within the EURAMET joint research project ‘Absolute Long-distance Measurement in Air’.