How To Test Laser Power On A Satellite

Transcription

1 UV LASER-INDUCED HYDROCARBON CONTAMINATION ON SPACE OPTICS Wolfgang Riede, Helmut Schröder German Aerospace Center (DLR e.v.), Institute of Technical Physics, Stuttgart, Germany Denny Wernham, Adrian Tighe ESA / ESTEC, Noordwijk, The Netherlands SRI Satellite Workshop: Carbon Contamination of Optics July

2 Contents of talk Introduction / Motivation LIC Test Bench / Test Procedure Monitoring / Phenomena Mitigation Summary / Outlook

3 DLR Test Center for Space-Based Laser Optics (Vacuum) Laser-Induced Damage Threshold (LIDT) Conversion Efficiency of NLO Crystals Laser-Induced (Molecular) Contamination (LIC) Vibration Tests on Mounted Samples High Energy Proton & Gamma Radiation (External Tests) Thermal Vacuum (External Tests)

4 Contents of talk Introduction / Motivation LIC Test Bench / Test Procedure Monitoring / Phenomena Mitigation Summary

5 Upcoming ESA Earth Observation Missions: ADM / EarthCARE LEO orbit (400 km) LEO orbit (450km) ADM Aeolus satellite* Global measurement of 3-dim. wind (speed) fields Predicted launch: Nov Projected lifetime: 36 months, shots Laser Instrument: ALADIN (Atmospheric Laser Doppler Instrument) Specs:50 Hz, ~ nm, XHG LBO, osc. / amp design EarthCARE satellite* Global measurement of vertical profiles of water & aerosols Predicted launch: 2016 Projected lifetime: 36 months, shots Laser Instrument: ATLID (Atmospheric LIDAR) Specs: 74 Hz, nm, XHG LBO, osc. / amp design *Durand et al.; LIDAR technology developments in support of ESA Earth Observer Missions, ICSO 2008

6 Laser-Induced (Surface) Contamination: General Definition of LIC: Formation of a deposit on the surface of an optical component due to the interaction between the laser beam, the surface of the optic and outgassing species from nearby materials. Affected applications (market): Vacuum operated laser systems (space applications) Pressurized sealed laser systems (military applications) UV lithography Synchrotrons Involved risks: Decrease of optical transmission Reduction of system lifetime System failure (permanent damage)

7 LIC-Related Standards ECSS-Q-70-01A: Cleanliness and contamination control (2008) Selection based upon low outgassing criteria, RML < 1 % and CVCM < 0,10 % CVCM: Collected Volatile Condensable Material RML: Recovered Mass Loss..for applications around sensitive items (e.g. optics and detectors) more stringent values should be used (bakes on the relevant hardware) ECSS-Q-70-02A: Thermal vacuum outgassing test for the screening of space materials NASA-STD-(I)-6016: Standard materials and processes requirements for spacecraft Materials that are line of sight to contamination sensitive surfaces.. shall have a 0.01 percent CVCM (windows, lenses,.. and other surfaces with highly controlled optical properties)

8 LIC-Related Standards (2) -> Currently no standard test method for measuring and quantifying laser-induced contamination! -> Recommended CVCM limit is to high! -> Agreed-on test benches & test procedures with ESA / ESTEC

9 Contents of talk Introduction / Motivation LIC Test Bench / Test Procedure Monitoring / Phenomena Mitigation Summary / Outlook

10 LIC Test Bench Principal optical set-up

11 Multibeam LIC test bench DLR Multibeam ultrahigh vacuum test chamber

12 Contamination test procedure 1. Vacuum bake-out: Bake-out: 24 hours, 180 C (UHV chamber), dynamic pu mping 2. Blank test: Laser operation (>24 h) under identical conditions as subsequent LIC test (temperature, duration, pressure), but without contaminant inside chamber Success criteria: no deposit on test optic / no transmission loss 3. LIC test: Insertion of weighted test specimen in chamber & system pump down to < 10-5 mbar Laser operation with online monitoring of fluorescence (LIF) Inspection of test optics Determination of mass loss of test specimen

13 Typical contamination test parameters Wavelength: λ = 1064 nm, 355 nm Pulse width: t = 3 ns / 10 ns Max. rep. Rate: ν = 100 Hz / 1 khz* Beam diameter: d = 300 µm - 3 mm Pulse energy: E = mj Peak fluence: F = J/cm 2 # shots: N = Contaminant pressure: 10-5 mbar Temperature T = C Contamination sample & optic * accelerated ageing

14 Contents of talk Introduction / Motivation LIC Test Bench / Test Procedure Monitoring / Phenomena Mitigation Summary / Outlook

15 Monitoring of Molecular Contamination Laser-induced fluorescence (LIF) Imaging Laser Transmission Measurement Residual Gas Analysis (RGA) - Mass Spectrometry Quartz Crystal Micro Balance (QCM) Nomarski Microscopy White Light Interference Microscopy Atomic Force Microscopy Time-of-flight SIMS Cavity Ring Down Spectroscopy In-situ / ex-situ

16 In-Situ LIF Imaging: Typical Test Set-Up Edge filter Silicone based glue 160 nm Spectral distribution of LIF of deposit

17 In-Situ LIF Imaging: Dynamic development 1 min 1 min Doughnut growth Pancake growth Pulsed UV irradiation cw UV irradiation (375 nm UV diode) 2.5 Jcm x 10 2 Wcm -2

18 In-Situ LIF Imaging: Dynamic development 5 min 5 min Doughnut growth Pancake growth Pulsed UV irradiation cw UV irradiation (375 nm UV diode) 2.5 Jcm x 10 2 Wcm -2

19 In-Situ LIF Imaging: Dynamic development 10 min 10 min Doughnut growth Pancake growth Pulsed UV irradiation cw UV irradiation (375 nm UV diode) 2.5 Jcm x 10 2 Wcm -2

20 In-Situ LIF Imaging: Dynamic development 25 min 25 min Doughnut growth Pancake growth Pulsed UV irradiation cw UV irradiation (375 nm UV diode) 2.5 Jcm x 10 2 Wcm -2

21 In-Situ LIF Imaging: Dynamic development 50 min 50 min Doughnut growth Pancake growth Pulsed UV irradiation cw UV irradiation (375 nm UV diode) 2.5 Jcm x 10 2 Wcm -2

22 In-Situ LIF Imaging: Dynamic development 60 min 60 min Doughnut growth Pancake growth Pulsed UV irradiation cw UV irradiation (375 nm UV diode) 2.5 Jcm x 10 2 Wcm -2

23 In-situ Transmittance -> Evolution of the ratio between the transmitted and incident energy UV beam splitter Test optics Feed-through with micrometric stage UV beam splitter Dump lens VACUUM CHAMBER Energy meter OUT Energy meter IN 111 Vdc Multimeters 111 Vdc Computer for continuous monitoring

24 In-Situ LIF Imaging / ex-situ Interferometry Test parameters*: Temperature: 100 C Contaminant: A12 epoxy Pressure: HV Wavelength: 355 nm Zygo height scan Fluorescence distribution Line scan overlay Good spatial correlation (thickness estimation by LIF) Detection sensitivity few nm! Test performed at ESA/ESTEC labs

25 Contents of talk Introduction / Motivation LIC Test Bench / Test Procedure Monitoring / Phenomena Mitigation Summary / Outlook

26 Fluence Effects 0.08 J/cm² 0.5 J/cm² 1 J/cm² 200 µm 200 µm 200 µm White light interference micrographs attained from different fluence values Existence of ablation thresholds 0.12 J/cm² for CV 2566 (silicone based glue) 355 nm, 40 C, 10 Mio. pulses

27 Substrate Effects Deposit height profiles for MgF 2 and SiO 2 substrates Deposit height profiles for differnent surface roughness values Deposit height is dependent on underlying surface

28 Environmental Effects Deposit height profile with and without water Deposit height profile for different surface temperatures of target optic Water & heating of target optic is mitigating (but not preventing) LIC

29 Wavelength Effects 1064 nm 355 nm CV 1152 (Silicone) T = 40 C T = 100 C Solithane 113 (Polyurethane) T = 40 C A12 (Epoxy) T = 100 C no deposit no deposit no deposit no deposit 30 nm > 1000 nm 10 nm > 50 nm Wavelength effects for identical test conditions (1 J/cm², 5 Mio. shots) Deposition in the UV much more severe

30 Deposition from cw UV laser sources Influence of surface temperature of target optic on deposit growth Sample preparation: Solithane nm 220 W/cm² 40 C, 24 hours p < 10-5 mbar cw UV lasers induce deposits

31 Laser induced contamination under ambient atmosphere Deposit growth / laser fluence 2-dim contour plot of deposit Irradiation parameters: Wavelength: 355 nm Pulse width: 10 ns Peak fluence: 3.1 J/cm² # Shots: 230 Mio. Contamination in air under the presence of silicones

32 Contents of talk Introduction / Motivation LIC Test Bench / Test Procedure Monitoring / Phenomena Mitigation Summary / Outlook

33 Shielding of Optics Shielding will not prevent deposition! Test with Shield Test without Shield Test performed at ESA/ESTEC labs

34 Material Bake-out Unbaked 7 nm thick deposit No Bake out Baked 1-2 nm thick deposit Bake out 18 Vacuum bake out reduces the outgassing flux and consequently the contamination, but does not prevent LIC Test performed at ESA/ESTEC labs

35 Prevention of LIC in low pressure O 2 atmosphere 5 Pa O 2 5 Pa 10 Pa O 2 10 Pa 20 Pa O 2 20 Pa LIC test with varying O 2 pressures LIC decreases with increasing O 2 pressure until LIC not detectable >20 Pa O 2 25 Pa Test performed at ESA/ESTEC labs

36 Prevention of LIC in low pressure O 2 atmosphere But: Oxygen pressure must match the amount of outgassing contaminant flux! (materials bake-out necessary) Test performed at ESA/ESTEC labs

37 Contents of talk Introduction / Motivation LIC Test Bench / Test Procedure Monitoring / Phenomena Mitigation Summary / Outlook

38 Summary (General) LIC is a significant risk to the performance of UV lasers (LIDARS) operating on space Available in-situ LIC monitoring techniques have nanometer resolution LIC fluence levels ~ 2 orders of magnitude lower than damage threshold Existence of deposition & ablation thresholds Deposits grow under UV cw laser irradiation Deposits built-up under ambient atmosphere under the presence of silicone based contaminants

39 Summary (Mitigation & Prevention) Screening of applied outgassing materials (for low deposit formation) Vacuum bake-out of materials used (space conditioning) Operation at low fluence values (~ mj/cm 2 ) Shielding & cold traps Operation under low pressure oxygen (artificial atmosphere) pressure threshold (20 25 Pa O 2 )

40 Thank you for your attention! Acknowledgements: ESA / ESTEC for continuing project support LZH for cooperation G. Taube / F. Hadinger for technical support

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42 ATLID EarthCare test bench Pressure: < 10-8 mbar Volume: 25 liters Sealing: Copper flanges DLR Ultrahigh vacuum test chamber for long term contamination tests

43 Motivation: Past / Present Space Laser Missions Instrument (Mission) LITE (Space shuttle STS-64) MOLA 2 (Mars Global Surveyor) GLAS (ICESat) CALIOP (CALIPSO) LALT (SELENE) Wavelengths [nm] / laser specs 1064, (532, 355) 10 Hz / 400 mj Total pulses [Mio] 1.16 / 0.77 Launch Notes Agency 1994 In space performance loss (epoxy contamination) % decline per year (MOLA 1: on ground silicone contamination) 1064 (532) 40 Hz / 75 mj 1064, Hz / 100 mj Hz / 100 mj > Laser 1: 30% decline per month (In solder contamination) Laser 2: degradation due to photo darkening on SHG Laser 1: Pressurized, switch to laser 2 after 3 years (leak) (still operating)? 2007 Mission end 2009 (20 Mio. data points) NASA NASA NASA NASA / CNES JAXA

44 Residual Gas Analysis - Mass Spectrometry Clean chamber

45 Residual Gas Analysis - Mass Spectrometry Cleanliness control Chamber exposed to Naphtalene

46 ToF-SIMS MgF 2 Silicone C x H y Mg 3 O 2 F Mg 3 O 3 H Deposition process radially selective 500 µm 10 nm Sample preparation: Silicone based glue 355 nm, 100 Hz, 3 ns 1.5 J/cm² 100 C, 5x10 6 shots AR coated MgF 2 top layers

47 Periodic Surface Ripples 5.5 µm polarization AFM micrograph 10 7 shots, 355 nm, DP490 (epoxy), 10-4 mbar 2.5 J/cm 2, Quartz window Ripple period: 280 nm Nomarski micrograph shots, 1064 nm, Toluene 0.1 mbar 0.22 J/cm 2, BK7 Ripple period: 550 nm Omnipresence of periodic surface ripples in deposit