1. M.Lintz, ICSO 2008 2 mode laser telemetry 1 "T2M": two-mode telemetry for high accuracy absolute distance measurement M. Lintz, C. Courde, A. Brillet, C. N. Man ARTEMIS, Observatoire de la Côte d'Azur 06300 NICE Funded by CNES PhD grant: Thales Alenia space and Région Provence-Alpes- Côte d'Azur Towards nanometric accuracy without interferometry

2. M.Lintz, ICSO 2008 2 mode laser telemetry 2 formation flights: need for high accuracy distance measurements over hundreds of meters 1µm as a first step...device small enough to get onboard a SC

3. M.Lintz, ICSO 2008 2 mode laser telemetry 3 - tune the frequency to get zero phase and measure F - then L meas -L ref = K  = K c/F (K integer) - tune to next zero L meas -L ref = (K+1) c/F'  K= F / (F'-F) HIGH ACCURACY The modulated laser beam technique: THE BASIC PRINCIPLE !! drifts  =c/F high frequency F phase difference L meas L ref...is not the best one! (with cyclic errors)

4. M.Lintz, ICSO 2008 2 mode laser telemetry 4 Polarisation controller polarisation analysis  PBS (x,y) phase signal  synth =c/F F ~13,01GHz 45° 13GHz phasemeter  (meas)  (ref) polarisation switching ~ kHz meas ref meas   ref unchanged when polarisation switching high accuracy phase zero tuned  (ref)-  (meas) +offset  (meas)-  (ref) +offset improved version

5. M.Lintz, ICSO 2008 2 mode laser telemetry 5 telemeter signal T2M (Two-mode telemeter) set-up Phase lock RF 10MHz slave laser +F, F=13GHz+10MHz master laser pol. contr. pol. analysis LI lock 2 kHz  AD 9901 lock  10MHz ref meas red: laser beams green: optical fibres black: HF (13GHz) blue: RF (10MHz) purple: DC-100kHz ~13GHz VCO 13,01GHz lock freq.meas  telemeter PBS (x,y)

6. M.Lintz, ICSO 2008 2 mode laser telemetry 6 The XOR phase-metre In 1In 2 OUT  phase-to-amplitude coupling 2  10 -3 for a 20% imbalance. in1/in2 - no polarisation switch - L meas scanned over 25mm 25 mm vs L VM phase signal

7. M.Lintz, ICSO 2008 2 mode laser telemetry 7 20µm 1mn Signal zeroes: the good ones, the bad ones...  BAD!  GOOD!noise subtraction! - "integer zero": L M -L R = Kc/F - "1/2-integer zero": L M -L R =(K+1/2)c/F 1/2integer zero integer zero

8. M.Lintz, ICSO 2008 2 mode laser telemetry 8 noise / systematics ? Polarisation change in the corner cubes? PBS Extinction defect? HF/RF crosstalk? Photodiode response? Optical return from photodiodes? Amplitude to phase coupling? Defect of the polarisation switch? Lock en phase RF 10MHz fixed frequency laser slave laser +F, F=13GHz+10MHz pol. control pol. analysis DS lock qq kHz  AD 9901 lock  10MHz ref meas. VCO 13GHz 13,01GHz NO YES YES, 1µm NO, not on "good" zeroes PBS cube YES ~5µm

9. M.Lintz, ICSO 2008 2 mode laser telemetry 9 20µm 1mn The polarisation routing defect - defect:  1% in intensity -  10% in AMPLITUDE the "noise" is due to the change of the interference order (L meas -L ref )/ opt with time  admixture (interference): meas +  ref, ref -  meas and  reverses with the polarisation switch! and amplitude-to-phase coupling RMS amplitude of the 10 MHz signal of Phd 1 Telemeter signal pol. control pol. analysis

10. M.Lintz, ICSO 2008 2 mode laser telemetry 10 (corrected) telemeter signal: long term stability "ref" VM "meas" "zero distance" stability test RMS Telemeter (raw) Telemeter (corrected)

11. M.Lintz, ICSO 2008 2 mode laser telemetry 11 Telemeter data: coherency (8m path) 2) Kc/F should be equal to (K+1)c/F'...=(K+N)c/F (N) etc... 1) K  F/(F'-F) has to be an integer distance to the next integer 5µm L(mm) with stat. error bars time series 2µm L(mm), selected data with low stat dispersion time series

12. M.Lintz, ICSO 2008 2 mode laser telemetry 12 Telemeter data: stability (8m path) Long term (in)stability in the 10µm range probably thermal expansion of the opt. breadboard To be checked in the future with separate telemeter (heretodyne interferometry) what about "nanometric" ?? 10µm "sub-micron"

13. M.Lintz, ICSO 2008 2 mode laser telemetry 13 T2M: how to get "nanometric" ? Signal amplitude problem: - improve polarisation controller (large drifts in the piezo squeezers) - reduce the residual amplitude effect (intensity control loop) - improve the phase-meter Optical return from the photodiodes: - switch to FC/APC, with -35dB return (instead of FC/PC, with -15dB return) - insert optical isolators - good AR coating for the collimator Goal: 10nm accuracy - without interferometry! - simple setup! closed loop noise on the telemeter signal (µm/  Hz) 1nm/  Hz

14. M.Lintz, ICSO 2008 2 mode laser telemetry 14