Launch your visions HIGH STABILITY LASER FOR INTERFEROMETRIC EARTH GRAVITY MEASUREMENTS K. Dahl, K. Nicklaus, M. Herding, X. Wang, N. Beller, O. Fitzau, M. Giesberts, M. Herper, R. A. Williams, G. P. Barwood, P. Lovelock, P. Gill, H. Koegel, A. Sell ICSO 2016, October 18, 2016
Introduction GOCE (ESA) Launch date: March 2009 1 spacecraft with GPS and gradiometer Mapping of Earth s gravity field Nov 2013: life in orbit ends GRACE (NASA/DLR) Launch date: March 2002 2 identical spacecraft 220 km apart microwave ranging instrument Mapping variations of the Earth s gravity field Still in operation with intermediate switch-off of instruments (battery capacity degradation) GRACE-FO (NASA/DLR) Scheduled for launch in 2017 2 spacecraft microwave instrument & laser ranging interferometer NGGM (ESA) Study phase 1 or more satellite pairs in loose formation laser ranging interferometer http://www.esa.int/our_activities/observing_the_earth/goce grace.jpl.nasa.gov Earth: NASA Blue Marble, satellites: Schütze/AEI GOCE GRACE GRACE FOLLOW-ON 18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 2
18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 3 HSL EBB Performance Requirements Requirement Parameter Requirement Value Optical output power > 500 mw Optical power stability < 10 3 Hz 1 + 10 mhz f 4 for 0. 1 mhz < f < 1 Hz Output wavelength (1064 ± 0.8)nm Frequency noise spectral density Wavelength tunability Spectral linewidth Spectral purity < 40 Hz Hz > 4GHz < 10 khz 1 + Spatial mode, M² TEM 00, M² < 1.2 Output polarisation Linear, > 100:1 Power consumption 10 mhz f < 45 db (nominal polarisation state) < 40 db (orthogonal polarisation state) < 50 W 2 for 0. 1 mhz < f < 1 Hz
High Stability Laser Architecture High Stability Laser (HSL): Laser head: Seed laser (NPRO) Fibre component box Pump module Laser head electronics Laser stabilization unit: Optical cavity assembly Laser stabilization electronics NPRO Pump Module Fibre Component Box Optical Cavity Assembly 18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 4
Laser Head: Seed Laser & Pump Module Both light sources are fibre coupled to fibre component box Seed Laser λ = 1064nm Operated at 20mW optical power Bandwidth < 10kHz RIN below requirement NPRO Pump Module Pump Module λ = 976nm Volume Bragg grating stabilized laser diode Using approx. 2W optical power Stand-alone unit allowing separation of heat sources in S/C 18 October 2016
18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 6 Radiation Test of Pump Module Total proton dose: 4 10 10 protons/cm² @ 36 MeV Total gamma dose: 20 krad No change in output power Significantly decreased locking factor (centre wavelength shifts up to approx. 0.4nm) pump diode is operated at an increased temperature F lock = 977 nm Pλ 975 nm P tot dλ
18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 7 Laser Head: Fibre Component Box All-fibre based amplifier w/ spliced fibre components Contra-directionally pumped active Yb-doped fibre 1 st Eigenfrequency at 521Hz > 500 mw optical output power Fibre Component Box
Laser Stabilization Unit Cubic cavity (50mm edge length) High finesse cavity (approx. 300,000) Ultra-low expansion material 10µW optical input power to cavity delivered by an optical fiber Operated in vacuum 1 st Eigenfrequency at 175Hz Pound-Drever-Hall locking scheme Cubic Cavity Optical Cavity Assembly 18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 8
18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 9 Performance Measurements Cavity FCB FCB Seeder Cavity Reference Lasers OGSE Test setup for optical performance measurement in Airbus Laboratory for Enabling Technologies
Performance Measurements Measurement at atmospheric pressure Interface temperatures: 20 C for pump module and fibre component box 25 C for optical cavity assembly 18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 10
Non-operational Thermal Cycling Test Devices under test Pump module (-40 C to +50 C) Fibre component box (-40 C to +50 C) Optical cavity assembly (-20 C to +50 C) Temperature rate of < 2 K/min Number of cycles: 3 Full performance after nonoperational thermal cycling test Optical Cavity Assembly inside thermal chamber Pump Module Fibre Component Box 18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 11
18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 12 HSL EBB Performance Results Requirement Parameter Requirement Value Measurement Value Optical output power > 500 mw 504 mw to 518 mw Optical power stability (for 0.1 mhz < f < 1 Hz) < 10 3 Hz 1 + 10 mhz f 4 < 10 3 Hz Output wavelength (1064 ± 0.8) nm 1064.12 nm Frequency noise spectral density (for 0.1 mhz < f < 1 Hz) < 40 Hz Hz 1 + 10 mhz f 2 < 20 Hz Hz 1 + 1 + 10 mhz f 10 mhz f Wavelength tunability > 4GHz > 7.9GHz (mode hop free) Spectral linewidth < 10 khz < 2.7kHz (free-running) Spectral purity < 45 db (nominal polarisation state) < 40 db (orthogonal polarisation state) < 65 db (nom. polarisation state) < 64 db (orth. polarisation state) Spatial mode, M² TEM 00, M² < 1.2 TEM 00, M² < 1.09 Output polarisation Linear, > 100:1 Linear, > 550:1 Power consumption < 50 W 50 W (lab power supplies) 4 2
gpk SRS Summary High Stability Laser Elegant Breadboard for NGGM developed Key performance requirements are met Non-Op. Thermal cycling successfully passed Environmental testing ongoing Outlook for the next year Ongoing environmental test campaign Operational and non-operational thermal vacuum testing of FPA Vibration test of FPA & cavity Shock test of FPA & cavity 1000 FPA design upgrade to improve TRL to 5 and to 7 on component level 10 100 1000 10000 Frequency [Hz] 18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 13 100
News from the lab Breadboard testing to identify limits of the amplifier setup with respect to the onset of nonlinear effects at single frequency operation Up to 5.5 W of optical output power with no indication of SBS achieved (Pump power limited) 18 October 2016 High Stability Laser for Interferometric Earth Gravity Measurements ICSO 2016 14
Launch your visions Thank you for your attention. The development of the HSL EBB has been funded by ESA in the frame of activity AO/1-6906/11/NL/SFe High-Stability Laser with Fibre Amplifier for Interferometric Earth Gravity Measurements - Laser Stabilisation Unit for Interferometric Earth Gravity Measurements. HIGH REPRODUCIBLE CO 2 LASER SPLICED FIBER- COLLIMATOR FOR A SPACE BORNE LASER SYSTEM OPTICAL ISOLATOR FOR SPACEBORNE HIGH POWER LASER SYSTEMS LASER RANGING INTERFEROMETER ON GRACE FOLLOW-ON