Alignment Control

of GEO 600

Hartmut Grotefor the GEO600 team

Institut für Atom- und MolekülphysikUniversity of Hannover

Max-Planck-Institut für Gravitationsphysik

9. July 2003

9. July 2003 Hartmut Grote

Autoalignment: Why ?

Superimpose beam axes

Maximize light power

Stabilze optical gain

Center beam spots on mirrors

Minimize angular to longitudinal noise coupling

9. July 2003 Hartmut Grote

Differrential wavefront sensing

(analog feedback for 14 DOF in GEO)

Spot position sensing

(digital feedback for 20 DOF in GEO)

Autoalignment: How ?

9. July 2003 Hartmut Grote

Modecleaner Autoalignment

Bandwidth: 1kHz

9. July 2003 Hartmut Grote

Modecleaner Reflected Power

Time [s]

Ref

lect

ed p

ower

[A

rb.]

Pitch DWS feedback

... and yaw DWS feedback

9. July 2003 Hartmut Grote

PR und MI Autoalignment

9. July 2003 Hartmut Grote

3 mm

Blades

Stack

Mirror

Magnet-CoilActuatorRange: 100 µm,Typ. DC-10 Hz

Intermediatemass

ElektrostaticActuatorRange: 1 µm (DC), Typ. 10-100 Hz

Double – Triple Pendulum

9. July 2003 Hartmut Grote

Processing square root with analog electronics

Peak force: 30 µNNeeded for acquisition

Maximal mirror speed with PR gain 300 is100 nm/s

Electrostatic Drive

9. July 2003 Hartmut Grote

Intermediate Mass Actuator

Alignment transfer function

Frequency [Hz]

Am

plit

ude

[Abs

.]

9. July 2003 Hartmut Grote

Michelson Power Levels

Time [s]

Time [s]

Lig

ht p

ower

[A

rb.]

Lig

ht p

ower

[A

rb.]

Dark port

PR cavity

9. July 2003 Hartmut Grote

Spectral Density of MI-DWS

Frequency [Hz]

Dif

fere

ntia

l MC

e/M

Cn

alig

nmrn

t [ra

d/sq

rt(H

z)]

Error signal

Feedback

9. July 2003 Hartmut Grote

DWS Feedback Noise

Noise coupling by spot position deviations

Angular noise in GW band(e.g. caused by DWS feedback)

RMS angular noise

RMS deviationfrom center of pitch / yaw

Induced length noise

9. July 2003 Hartmut Grote

Michelson Strain Sensitivity

S1

Sqrt-noise

HV-amplifier noise

Michelson DWS feedback noise (1mm)

Frequency [Hz]

Str

ain

sens

itivi

ty [

1/sq

rt(H

z)]

Noise limit

9. July 2003 Hartmut Grote

PR and MI Autoalignment

Matrix diagonalizationfor 4 dimensions

9. July 2003 Hartmut Grote

Computer Control

9. July 2003 Hartmut Grote

Operation during S1

98% duty cycle, almost no human interaction required

Time

Time [days]

Time [days]

Tem

p. [

Deg

. C]

BS

pitc

h F

B [

µra

d]

9. July 2003 Hartmut Grote

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

9. July 2003 Hartmut Grote

9. July 2003 Hartmut Grote

9. July 2003 Hartmut Grote

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

Sensitivity typically 10 p rad / sqrt(Hz)

Differential Wavefront Sensing

9. July 2003 Hartmut Grote

Modelliertes Alignment am PR MI

9. July 2003 Hartmut Grote

Michelson Error Signal

A larger mismatch in the radii of curvature makes the system more sensitive to misalignment.

9. July 2003 Hartmut Grote

Autoalignment

Experimental setupfor 1 cavity

9. July 2003 Hartmut Grote

Autoalignment

Experimental setupfor 1 cavity

Differential wavefrontsensing

Orthogonalization< 1/10

Bandwith 0.2 or 6 Hz

9. July 2003 Hartmut Grote

Autoalignment

Experimental setupfor 1 cavity

Local beam centeringservos

Bandwidth ~ 1kHz

9. July 2003 Hartmut Grote

Autoalignment

Experimental setupfor 1 cavity

Spot position control

9. July 2003 Hartmut Grote

Autoalignment setup

PR + MI cavity

9. July 2003 Hartmut Grote

Misalignment eines Resonators

Messe Winkel zwischen Wellenfronten an zwei verschiedenen Positionen

Achse der Eigenmode

Achse des eintretenden Strahls