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Power Stabilization to 3E-9 level

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Power Stabilization to 3E-9 level

Frank Seifert, Patrick Kwee, Michele Heurs

Benno Willke, Karsten Danzmann

Max-Planck-Institute for Gravitational Physics(Albert-Einstein-Institute)

University of Hannover

LSC Hanford, March 21th, 2006

LIGO-G060115-00-Z

Max Planck Institute for Gravitational Physics

(Albert Einstein Institute)

New Power Stabilization Setup

- laser system:- as simple as possible- prevent x-coupling of laser diode current into other observables (frequency, beam geometry, etc.)
NPRO &power actuator independent from laser system (e.g. AOM)

- beam pointing:- may limit at 10-9-level at low frequencies- filtering or active stabilization required ?- use of different photodiodes? (larger ?) filtering by PMC (F≈4100) & whole setup in vacuum & same photodiodes as before
- photodiode temperature:- chip temperature increases ≈ 10K (P=130mW)- temperature coefficient ≈ 0.039 %/K (Datasheet Perkin Elmer) active temperature stabilization
- optimization of stabilization loop- DC-coupled loop for stable operating point- AC-coupled loop for lowest noise DC & AC-coupled loop

power stabilization to 3E-9 level - AEI Hannover

DC & AC-coupled loop - Principle

Advantage:

- DC-coupled loop for stable operating point- AC-coupled loop for lowest noise (not limited by noise of voltage reference)

power stabilization to 3E-9 level - AEI Hannover

Power Stabilization Setup

power stabilization to 3E-9 level - AEI Hannover

Results – DC & AC Coupled Loop

Shot noise level 2E-9

power stabilization to 3E-9 level - AEI Hannover

Critical Factors

- very (!) sensitive to ground loops avoid any (!) ground loop, even at RF (capacitive coupling) independent supply of components battery powered devices
- beam pointing reduction by PMC (passive filtering) proper adjustment of photodiodes (minimize with impressed pointing) (PZT behind PMC)
- acoustics shielded environment proper mechanical design
- air currentsvacuum

power stabilization to 3E-9 level - AEI Hannover

Photodiode Non-uniformity & Pointing

spatial uniformity measurement

pointing measurement

(when) does it limit the performance ?

power stabilization to 3E-9 level - AEI Hannover

Pointing Sensitivity Measurement

EG&G C30642G

3 different methods very good agreement

power stabilization to 3E-9 level - AEI Hannover

Low Frequency Noise in PD‘s

Balanced detection setup

- pre-stabilized laser system below 1E-8 level
- amplification aftersubstraction of photocurrents
- temperature stabilized photodiodes
- vacuum tank

power stabilization to 3E-9 level - AEI Hannover

Balanced Detection Setup

power stabilization to 3E-9 level - AEI Hannover

Balanced Detection – First Experiment

unknown noise source

nearly shot noise limited

first test of balanced detection setup with large area Si photodiodeswithout temperature stabilization:

power stabilization to 3E-9 level - AEI Hannover

Balanced Detection – Results (1)

bias voltage dependence:

power stabilization to 3E-9 level - AEI Hannover

Balanced Detection – Results (2)

temperature dependence:

power stabilization to 3E-9 level - AEI Hannover

Low Frequency Limit

:

PD low frequency noise limiting ?:

differentphotodiodes !!

power stabilization to 3E-9 level - AEI Hannover

Conclusion & Next Steps

- Still limited by unidentified noise source at low frequencies low frequency noise in PD‘s good candidate
- future experiments:
- low frequency noise in photodiodes detailed characterization of different photodiodes (dependence on bias voltage, temperature, photocurrent, manufacturer, material (InGaAs, Ge), size (2mm, 3mm))
- influence of temperature fluctuations at the beamsplitter temperature coefficient of the BS TF temperature to RIN
- influence of photodiode temperature fluctutionstemperature coefficient of PD‘s TF temperature to RIN

power stabilization to 3E-9 level - AEI Hannover

spare slides

power stabilization to 3E-9 level - AEI Hannover

Photodiode Temperature Measurements

P = 65 mW

P = 105 mW

P = 130 mW

- ∆T only ≈ 10K
- real chip temperature ?

P = 0 mW

PD EG&G C30642G

without window

power stabilization to 3E-9 level - AEI Hannover

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