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LIGO-?????????

Photon Calibration System (PhotonCal)

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PhotonCal Functions

• Using photon radiation pressure, apply sinusoidally varying forces to each ETM which can be used to calibrate the displacement response of the aLIGO interferometers.

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PhotonCal Requirements

• Force sufficient to produce calibration lines at frequencies up to 500 Hz with a SNR>10 over the expected aLIGO sensitivity curve for integration times of 1 s.

• Absolute displacement calibration accuracy of 5% or better.• Mean Time Between Failures of at least one year for out-of-vacuum

components and three years for in-vacuum components• Periodic calibration of each PhotonCal system (each ETM) shall require

no more than one day to perform.

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PhotonCal Design Concept - 1

• Similar to that of iLIGO and eLIGO » Diode pumped solid state laser output at 1047 nm is sinusoidally

modulated using an acousto-optic modulator» Two-beam configuration to minimize elastic deformation of center of

optic and minimize induced rotation.» Absolute power calibration via integrating spheres using

temperature-controlled InGaAs photodetectors, with a “gold standard” calibrated at NIST.

• Changes for aLIGO» Higher-power lasers (1 – 1.5 W)» Reflected laser beams directed out-of-vacuum envelope to

calibrated receiver.» “Optical follower” servo loop to reduce modulation harmonics.

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PhotonCal Design Concept - 2

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Integrating spheres for absolutePowercalibration

1047 nmNd:YAGlaser

Acousto-opticmodulator

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PhotonCal Development Accomplishments - 1

• Understanding of the elastic deformations of the ETMs and how they can introduce errors in the calibration.» Locate PhotonCal beams at nodes of the drumhead mode.

• Reduction of systematic and statistical uncertainties to the few percent level. » Comparison with other calibration methods.

• Long-term stability of PhotonCal calibration of DARM actuation» Better than 0.5% (one sigma) over 8 months of S6.

• Test of aLIGO two-beam optical configuration. • Conceptual design of aLIGO transmitter and receiver support piers and

in-vacuum relay optics.

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PhotonCal Development Accomplishments - 2

• DARM_CRTL_EXC calibration (> 8 mos of S6)» Mean 1.28 nm/ ct ; standard deviation 0.28%

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PhotonCal Development Status

• In preliminary design phase» aLIGO PhotonCal “prototypes” operating on H1 and L1

interferometers during S6• Currently deferred due to lack of FY10 operations funds. In

FY11 operations budget.» Out-of-vacuum hardware not useful until within a factor of

~10 of design sensitivity.» Design of in-vacuum hardware and support piers on best

effort basis. May not be ready in time for H2 single-arm test.• PDR – October 2010 (goal)• FDR – March 2010 (goal)

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PhotonCal Project Organization

• Leader – Rick Savage• Michael Sakosky

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PhotonCal Project Phase Status

• Not yet in the Project. The design of the support piers is proceeding due to their similarity and interfaces with the optical lever piers. We would like to install them at the same time to concentrate similar, dirty activites.

• If in the Project phase for any part of your endeavor, report here technical accomplishments and status (money etc. in other presentation)

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PhotonCal Challenges, Risks, and Mitigations

• Low challenge level• No known risks in the Risk Registry• Rick have I forgotten one? Not that I

am aware of (rick)

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PhotonCal Near Term Activities

• Begin elastic deformation investigations for aLIGO ETMs with electro-static actuators (UTB)

• Prototype and test “optical follower” servo for improvement of output waveform (reduction of modulation harmonics).

• Complete preliminary design (goal)• Complete design of support piers

and in-vacuum hardware support rings.

• Continue eLIGO PhotonCal measurements and investigations.

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