ICSO High Accuracy Laser Telemetry for Kilometric Distance Measurement in Space C.COURDE, H. PHUNG Duy, M. LINTZ, A. BRILLET ARTEMIS, Observatoire de la Côte d'Azur CNRS et Univ. Nice-Sophia Antipolis NICE

ICSO Objectives  Absolute long distance measurement (~km) in vacuum with high accuracy  For : –Formation Flying telescope (Darwin (30µm of accuracy)) –Alignement and monitoring of large structure (particle colliders or radio telescope) DARWIN Our goal Range : ~ 1km Accuracy : < 1µm Resolution: ~nm

ICSO Outline I.T2M telemeter Principle Results II.Iliade telemeter Principle Results

ICSO I.T2M Principle t Δ  ref/mes  locked at 0 mes ref Λ Calibration with K integer and c the speed of light Amplitude Modulated beam Λ=c/F Synthetic wavelength Reference path Measurement path Δ  ref/mes Adjustable frequency F Accuracy limited by phase drifts and cyclic errors Robust and simple system  Corner cube

ICSO I.T2M Principle Elimination of systematic errors Amplitude modulated beam Λ=c/F Synthetic wavelength Reference path Measurement path ΔΔ Adjustable frequency F PHD1 PHD2 Crosstalk Cyclic errors are suppressed with the optical switching system Unbiased zero of phase difference Exchange of the beams between the two photodiodes Corner cube Optical switching system

ICSO  Frequency -meter VCO 13GHz PHD ASE SOURCE 1.55 µm Fibered PBS 2 kHz switch LI-A Telemetric lock Optical isolator Polarization controller 2 PBS cube Corner cubes Mixer HF phase-meter Δφ ref measure Telemetric signal I.T2M Principle Lock-in Amplifier Polarization controller 1 Amplitude modulator DISTANCE Optical switching system HF

ICSO I.T2M results Allan deviation of the Telemetric signal in open loop with a broadband source (ASE) Allan deviation < 20 nm for 5s < times < 2000s Probably limited At short measurement times by intensity noise of the source At long measurement times by systematic error To identify parasitic interferences : Broadband source+modulator is replaced by the beat note of two single mode lasers shifted by 13 GHz 10 nm

ICSO I.T2M characterization Searching for optical interferences Systematic errors !!! 4GHz 5µm Manual master laser wavelength scan 2 different cavity effects FSR 4GHz  thickness 37mm (vacuum) or 25mm (n=1.5) FSR 270MHz  thickness 56cm (vacuum) or 37cm (n=1.5) 2µm Slow length scan Telemetric signal PBS cube SOLUTION Freq markers - PBS cube changed for a thick polarization beam splitter at 45° Manual master laser wavelength scan Telemetric signal Systematic errors lower than 1 µm 4GHz Freq markers

ICSO II.Iliade principle Combining 3 levels of increasing sensitivity: Time of flight measurement of optical pulses => Absolute distance measurement 0.1 mm 15 mm0.1 µm Phase measurement of synthetic wavelength => relative distance measurement 1.55 µm 0.1 nm Phase measurement of optical wavelength => relative distance measurement In PhD1 Synthetic angular frequency Optical angular frequency

ICSO II.Iliade preliminary results Simulation Varying L, All parameters fixed Experiment « segment » for different positions with 0.5mm increments at a 1.5m Distance Use of the interference figure : Varying allows to cover the « segment » Deviations of peak-peak Non-linearity in commercial oscilloscope used for data acquisition

ICSO Conclusion –T2M Simple system with accuracy fixed by the frequency measurement No optical stabilization Systematic errors lower than 1 µm, to be confirmed Stability below 20 nm for measurement times [5s,2000s] –Iliade Principle of the measurement is confirmed Limitations in phase measurements and in amplitude measurements caused by non linearity in the data acquisition system

ICSO Thanks to CNES ANR Thales Alenia Space région PACA and thank for your attention