1 Detector meeting, October 4 th 2006 M Laval Thermal effects and PR misalignments Virgo simulations with the input mirror absorption losses calculated.

1 Detector meeting, October 4th 2006M Laval

Thermal effects and PR Thermal effects and PR misalignments misalignments

Virgo simulations with the input mirror absorption losses calculated by Michele Punturo.

Effects of a PR tilt on the recycling gains (carrier and sidebands)•Without thermal effects (mirror map influences)•With thermal effects

Tools: • The optical simulation code DarkF (fortran90)Authors: -Jean Yves Vinet (OCA/ARTEMIS)

-Mikael Laval (OCA/ARTEMIS)

Approximation: No maps used for the beam splitter


Thermal effects on the recycling gainsThermal effects on the recycling gains

• Initial absorption losses measured at the SMA of Lyon :NI : 1.25ppm Rc(thermal lens) = -58.7km (map fit with dx=1.56mm)WI : 1.38ppm Rc(thermal lens) = -53.2km (map fit with dx=1.56mm)

• Absorption losses calculated by Michele Punturo :

NI: 5ppm Rc(thermal lens) = -14.7km (map fit with dx=1.56mm)WI: 13.8ppm Rc(thermal lens) = -5.3km (map fit with dx=1.56mm)

The absorption losses of the input mirror high reflectivity coating determine the main thermal effects in Virgo but with time (and a possible pollution of the mirror surfaces) they have probably changed with respect to the measured values at the SMA of Lyon. Main effect = input mirror substrates become a converging lens

What are the absorption losses of the input mirrors?

The values of Rc are calculated for a power of 5kW in the long arms.


Comparisons of the recycling gains between Virgo and optical simulations (DarkF)

Values measured by Virgo:

At the beginning of the lock : G(carrier)=40 G(sidebands)=30

After the thermal stabilization : G(carrier)=41-42 G(sidebands)=11

Values simulated by DarkF (sampling step=1.56mm ; injected power=7W):

Without thermal effects :

With thermal effects (LY):

With thermal effects (MP):

G(C)=45.2 G(LSB)=43.5 G(USB)=32.2

G(C)=45.2 G(LSB)=42.6 G(USB)=43.0

G(C)=45.0 G(LSB)=3.4 G(USB)=11.3

Nomenclature: C=Carrier ; LSB=Lower Sideband ; USB=Upper sideband

LY = with absorption losses measured by Lyon

MP = with absorption losses calculated by Michele Punturo


Shape of the dark fringe on B1p

Virgo locked at step 12 DarkF

The absorption parameters have an important effect on the recycling gains of the sidebands. The results between Virgo and DarkF seems to confirm the absorption parameters calculated by Michele Punturo.

Conclusion:Conclusion:


Effects of a tilt of PR on the recycling gainsEffects of a tilt of PR on the recycling gains(suggested by Julien Marque)(suggested by Julien Marque)

Impact of the mirror maps on the recycling gains:

There are some unstable cases (the carrier does not converge):•without mirror maps: θy= ± 0.7 μrad ; θy= ± 0.8 μrad

•with end mirror maps and input mirror transmission maps (only):

θy= -1.3 μrad ; θy= -1.4 μrad ; θy= ± 0.7 μrad


The mirror maps (high reflectivity coating and transmission) have a big impact on the recycling gain of the carrier and of the upper sideband. The cause (residual curvature or flatness) will have to be determined.

Impact of the mirror maps on the recycling gains (2/3)


Impact of the mirror maps on the recycling gains (3/3)

Mirror surfaces parameters (fits weighted by a centered gaussian beam on maps given by Lyon with dx=0.35mm):

Mirror Map Curvature radius RMS flatness

NE High reflectivity coating 3583.1m 2.83nm

WE High reflectivity coating 3623.6m 3.63nm

NI High reflectivity coating 73.9km 1.73nm

NI Transmission 68.6km 1.62nm

WI High reflectivity coating 189,1km 1.15nm

WI Transmission 108.3km 1.19nm

PR High reflectivity coating -1351.0km 0.89nm

BS High reflectivity coating 142.2km 1.20nm

Coating maps: always seen in front view (substrate behind the coating) Rc>0 concave mirror

transmission maps: Rc>0 diverging lens

Why PR has an impact on the upper sideband recycling gain (to be done)?


Addition of the thermal effects

CarrierLower sidebandUpper sideband


Ratio between sideband recycling gains

Some results of the scanning Fabry Perot showed a dissymmetry between both sidebands but in the last ones, the dissymmetry had disappeared. A different alignment of PR could explain these different results.


ConclusionConclusion

The simulation seems to confirm the input mirror coating absorptions calculated by Michele Punturo.

Mirror maps are very important to simulate the thermal effects. They can not be neglected.

Variation of the PR alignment could explain the variations between sideband amplitudes on the scanning Fabry Perot.


To be doneTo be done

To determine the effects of a new increase of the injected power in Virgo for the sidebands.

To explain the dissymmetry between both sidebands in the recycling cavity.

What is the most important factor for the flat mirrors:flatness or residual curvature?

What are the effects of the Beam splitter?


More details for the Carrier


More details for the Lower Sideband


More details for the Upper Sideband


Shape of the dark fringe (1/3)

Without thermal effects



With the absorption losses measured by the SMA of Lyon



With the absorption losses calculated by M Punturo


Recycled beams (1/3)









Beam reflected to the laser (1/3)








1 Detector meeting, October 4 th 2006 M Laval Thermal effects and PR misalignments Virgo simulations with the input mirror absorption losses calculated.

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