Work on Coatings Wolfgang Riede, Paul Allenspacher Institute of - - PowerPoint PPT Presentation

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Work on Coatings Wolfgang Riede, Paul Allenspacher Institute of - - PowerPoint PPT Presentation

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Work on Coatings Wolfgang Riede, Paul Allenspacher Institute of Technical Physics, DLR Stuttgart, Pfaffenwaldring 38 40, 70 569 Stuttgart, Germany E-Mail: Wolfgang.Riede@dlr.de ESA-NASA Working Meeting on Optoelectronics: Qualification of

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Work on Coatings

Wolfgang Riede, Paul Allenspacher

Institute of Technical Physics, DLR Stuttgart, Pfaffenwaldring 38 – 40, 70 569 Stuttgart, Germany E-Mail: Wolfgang.Riede@dlr.de

ESA-NASA Working Meeting on Optoelectronics: Qualification of Technologies and Lessons Learned from Satellite LIDAR and Altimeter Missions; June 21, 2006

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Introduction

Motivation:

  • > Qualification of optics for ADM-Aeolus mission (ALADIN instrument)
  • > Extensive test campaigns (IR, UV, VIS) to identify optics exposed to critical fluence levels

Issues: Testing under application-oriented conditions (high vacuum, dry pump systems, laser parameters comparable to the ALADIN laser system)

  • > Development of a vacuum laser damage test bench

Important aspects: Scaling of LIDT to Gshot levels from data based up to 104 shots/site ? Vacuum effect on coating performance ?

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Nd:YAG Laser

lambda/2 plate Aperture 3 mm Optical shutters Pulse counter f = 500 mm x y HeNe (stab.) Wedge 12 bit CCD Flow box area Sample under vacuum

PC

Pol.

SHG / THG unit

Low noise diode HR HR HR Pyroelectric detector Chopper 3 kHz 600 mm

Laser damage test bench: IR optical setup

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Nd:YAG Laser

lambda/2 plate Aperture 2.2 mm Optical shutters Pulse counter f = 750 mm x y HeNe (stab.) Wedge 12 bit CCD Flow box area Sample under vacuum

PC

Pol.

SHG / THG unit

Low noise diode HR HR HR Pyroelectric detector Pyroelectric detector Chopper 3 kHz 600 mm

Laser damage test bench: UV optical setup

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wavelength 1064 nm repetition rate 100 Hz pulse energy 400 mJ pulse duration (FWHM) 3.5 ns pointing stability (long term) < 20 µrad/h beam quality M2 < 1.5 linewidth < 250 MHz repetition rate < 0.001 % pulse to pulse energy stability < 1.3 % pulse to pulse spatial profile stability < 3.3 % pulse to pulse temporal profile stability < 5 % pulse to pulse pointing stability < 10 µrad wavelength 355 nm pulse energy (IR pump energy 300 mJ) 70 mJ pulse duration (FWHM) 3 ns pulse to pulse energy stability (IR pump energy 200 mJ) < 3 % pulse energy stability long term (40 min) (IR pump energy 200 mJ) < 3 % pulse to pulse spatial profile stability < 3 % spatial profile stability long term (40 min) < 2 % pulse to pulse pointing stability (horizontal / vertical direction) < 25 µrad pointing stability long term (40 min) (horizontal / vertical direction) < 25 µrad

Laser damage test bench: specs and error budget of laser source

500 1000 1500 2000 50 100 150 200 Intensity [a.u.] Position [µm]

  • 200 -150 -100
  • 50

50 100 150 200 50 100 150 200 250

Intensity [a.u.] Position [µm]

Far field beam profiles (lhs: IR, rhs: UV)

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diode lens beam stop sample pressure sensor

Nd:YAG (1 w) HeNe Nd:YAG (3 w)

  • 5

5 10 0,0 0,5 3,90 3,95 4,00 4,05 4,10 4,15 4,20

2 pulses 0.37 J/cm

2

pressure signal scatter probe signal laser pulses

Signal [a.u.] Pulses

  • 5

5 10 0,0 3,90 3,95 4,00 4,05 4,10 4,15 4,20

0.29 J/cm

2

Signal [a.u.]

pressure signal scatter probe signal laser pulses

Pulses

Background pressure: 18 10-6 mbar Typical pressure rise: 4…8 10-6 mbar

Damage monitoring via scatter probing and transient pressure sensing

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  • Test of scattering samples (light trap absorbers)
  • Vibration insensitive
  • Misalignment (drift) insensitive
  • Useful as backup signal
  • Fast (up to kHz bandwidth)
  • No interference with optical channels
  • Sensitive to front and back surface
  • No detection of bulk damage!

Features of the transient pressure sensing

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Laser damage test bench: 1w / 3 w beamline / multi-functional vacuum chamber

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Data acquisition up to 800 Hz, multi channel Automation status semi- / fully automated Energy preselection algorithm binary / random; input & output parameter: pulse energy Sample positioning completely inside vacuum Laser wavelengths 1w & (2w; 3w) separate beam lines Mode of operation burst (intermittent) / non-burst operation Typical vacuum quality 5 10-6 mbar, oil-free pump system Laser beam analysis 12 bit CCD, 4.4 µm pitch (Spiricon FireWire);

  • nline beam profiling; adaptation to sample position

Damage detection modes

  • 1. Lock-in based, collinear scatter probing
  • 2. transient pressure sensing, cold cathode sensor

Lifetime testing up to 50 Mio. Shots (flashlamp lifetime)

Main features of damage test bench

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1 10 100 1000 10000 100000 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0

F = F1 e

  • N/c1 + F2 N
  • c2

Fluence F [J/cm

2]

Number of pulses N

sample: ES_LC_AR_096 pressure: 5 10

  • 6mbar

Chi^2 = 0.00498 R^2 = 0.98613 c1 10.13052 ±1.50773 c2 0.01201±0.00305 F1 3.81689±0.5483 F2 5.09429±0.10386

Empirical fitting curve: F = F1*exp[-N/c1] + F2*N-c2 exponentially decaying part F1*exp[-N/c1]; slowly decaying part F2*N-c2

  • > valid for all types of samples tested
  • > valid for 1064 nm / 355 nm wavelength
  • > independent of atmospheric conditions

Characteristic damage curve: laser fatigue effect

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Degradation under vacuum

1 10 100 1000 10000 100000 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0

F = F1 e

  • N/c1 + F2 N
  • c2

Fluence F [J/cm

2]

Number of pulses N

sample: ES_LC_AR_096 pressure: 1000 mbar N2

Chi^2 = 0.00105 R^2 = 0.99776 c1 5.79939 ±0.32053 c2 0.00051 ±0.00108 F1 3.18984 ±0.13933 F2 5.62741 ±0.04031

1 10 100 1000 10000 100000 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0

F = F1 e

  • N/c1 + F2 N
  • c2

Fluence F [J/cm

2]

Number of pulses N

sample: ES_LC_AR_096 pressure: 5 10

  • 6mbar

Chi^2 = 0.00498 R^2 = 0.98613 c1 10.13052 ±1.50773 c2 0.01201±0.00305 F1 3.81689±0.5483 F2 5.09429±0.10386

Vacuum 1 bar N2

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1 10 100 1000 10000 100000 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0

F = F1 e

  • N/c1 + F2 N
  • c2

Fluence F [J/cm

2]

Number of pulses N

Sample: ES_LC_AR_099 pressure: 5x10

  • 1mbar - 5 10
  • 5 mbar

Chi^2 = 0.01148 R^2 = 0.945 c1 12.90994 ±5.09142 c2 0.00759±0.00434 F1 1.21662±0.27352 F2 5.72651±0.16983

1 10 100 1000 10000 100000 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0

F = F1 e

  • N/c1 + F2 N
  • c2

Fluence F [J/cm ] Number of pulses N

2 Sample: ES_LC_AR_098 pressure: 4 bar (He)

Chi^2 = 0.00425 R^2 = 0.97465 c1 10.65326 ±3.21496 c2 0.00984±0.00263 F1 1.82971±0.53515 F2 5.76169±0.10323

4 bar He

Effect of gas thermal conductivity

vacuum

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1 10 100 1000 10000 100000 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0

F = F1 e

  • N/c1 + F2 N
  • c2

Fluence F [J/cm

2]

Number of pulses N

Sample: ES_LC_AR_099 pressure: 5x10

  • 1mbar - 5 10
  • 5 mbar

Chi^2 = 0.01148 R^2 = 0.945 c1 12.90994 ±5.09142 c2 0.00759±0.00434 F1 1.21662±0.27352 F2 5.72651±0.16983

1 10 100 1000 10000 100000 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0

F = F1 e

  • N/c1 + F2 N
  • c2

Fluence F [J/cm ] Number of pulses N

2 Sample: ES_LC_AR_099 pressure: 5 10

  • 6 mbar

Chi^2 = 0.00273 R^2 = 0.98766 c1 33.22866 ±8.58043 c2 0.01121±0.00396 F1 0.75737±0.1074 F2 5.14173±0.13947

42 h under vacuum

Effect of vacuum residence time

Immediate testing

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LIDT-tested ALADIN laser optic components (wavelength 1064 nm)

* Stated are „best LIDT values“ for tested types of optics

testing of 14 different types of optics, 38 samples overall

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LIDT-tested ALADIN laser optic components (wavelength 355 nm)

* Stated are „best LIDT values“ for tested types of optics

testing of 8 different types of optics, 22 samples overall

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Summary

Test bench for LIDT vacuum testing at 355 nm / 532 nm / 1064 nm Transient pressure sensing technique: suitable in a vacuum environment for online detection of laser damage Air – vacuum effect: small negative fluence offset found under vacuum indication residence time effects thermal isolation under vacuum (no thermal conductivity -> no ambient gas) must be excluded as cause of vacuum degradation. Laser fatigue effect: step-like degradation within several pulses leveling off along a slowly decreasing ramp (> 100 shots applied per site)

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Last not least: The support by the European Space Agency, Galileo Avionica and Astrium-F is gratefully acknowledged! Thank you for your attention!