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Alignment Control of GEO 600. Hartmut Grote for the GEO600 team Institut für Atom- und Molekülphysik University of Hannover Max-Planck-Institut für Gravitationsphysik 9. July 2003. Autoalignment: Why ?. Superimpose beam axes Maximize light power Stabilze optical gain

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alignment control of geo 600

Alignment Control of GEO 600

Hartmut Grote

for the GEO600 team

Institut für Atom- und Molekülphysik

University of Hannover

Max-Planck-Institut für Gravitationsphysik

9. July 2003

autoalignment why
Autoalignment: Why ?
  • Superimpose beam axes
    • Maximize light power
    • Stabilze optical gain
  • Center beam spots on mirrors
    • Minimize angular to longitudinal noise coupling
autoalignment how
Autoalignment: How ?
  • Differrential wavefront sensing

(analog feedback for 14 DOF in GEO)

  • Spot position sensing

(digital feedback for 20 DOF in GEO)

modecleaner reflected power
Modecleaner Reflected Power

Pitch DWS feedback

... and yaw DWS feedback

Reflected power [Arb.]

Time [s]

double triple pendulum
Double – Triple Pendulum

Blades

Stack

Magnet-Coil

Actuator

Range: 100 µm,

Typ. DC-10Hz

Intermediate

mass

Mirror

Elektrostatic

Actuator

Range: 1 µm (DC),

Typ. 10-100Hz

3mm

electrostatic drive
Electrostatic Drive

Processing square root

with analog electronics

Peak force: 30 µN

Needed for acquisition

Maximal mirror speed

with PR gain 300 is

100 nm/s

intermediate mass actuator
Intermediate Mass Actuator

Alignment transfer function

Amplitude [Abs.]

Frequency [Hz]

michelson power levels
Michelson Power Levels

Dark port

Light power [Arb.]

Time [s]

Light power [Arb.]

PR cavity

Time [s]

spectral density of mi dws
Spectral Density of MI-DWS

Feedback

Differential MCe/MCn alignmrnt [rad/sqrt(Hz)]

Error signal

Frequency [Hz]

dws feedback noise
DWS Feedback Noise
  • Noise coupling by spot position deviations

Induced length noise

RMS deviation

from center of

pitch / yaw

RMS angular noise

Angular noise in GW band

(e.g. caused by DWS feedback)

michelson strain sensitivity
Michelson Strain Sensitivity

S1

Sqrt-noise

HV-amplifier noise

Strain sensitivity [1/sqrt(Hz)]

Noise limit

Michelson DWS feedback noise (1mm)

Frequency [Hz]

pr and mi autoalignment
PR and MI Autoalignment

Matrix diagonalization

for 4 dimensions

operation during s1
Operation during S1
  • 98% duty cycle, almost no human interaction required

BS pitch FB [µrad]

Time [days]

Temp. [Deg. C]

Time [days]

Time

summary and outlook
Summary and Outlook
  • Autoalignment for modecleaners and power recycled Michelson complete (14 DOF DWS, 20 DOF spot pos.)
  • Long term stable operation achieved (~98% duty cycle during S1, longest lock >121 hours)
  • Michelson DWS feedback needs 10-20dB more gain at 0.5-2 Hz (reach 10nradRMS for MI arms)
  • Signal recycling DWS feedback in near future
differential wavefront sensing
Differential Wavefront Sensing

Detect angle between wavefronts in “near-“ and “far“ field

  • Sensitivity typically 10 p rad / sqrt(Hz)
slide23

Autoalignment

Experimental setup

for 1 cavity

slide24

Autoalignment

Experimental setup

for 1 cavity

Differential wavefront

sensing

Orthogonalization

< 1/10

Bandwith 0.2 or 6 Hz

slide25

Autoalignment

Experimental setup

for 1 cavity

Local beam centering

servos

Bandwidth ~ 1kHz

slide26

Autoalignment

Experimental setup

for 1 cavity

Spot position control

slide27

Autoalignment setup

PR + MI cavity

misalignment eines resonators
Misalignment eines Resonators

Achse der Eigenmode

Achse des eintretenden Strahls

Messe Winkel zwischen Wellenfronten

an zwei verschiedenen Positionen