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Thermal Headaches in Advanced LIGO Input Optics

Thermal Headaches in Advanced LIGO Input Optics Guido Mueller, Rupal Amin, David Guagliardo, David Tanner, and David Reitze Physics Department University of Florida Gainesville, FL. LIGO-G010130-00-Z. Input Optics Functions. RF Modulation Mode Cleaning Mode Matching Optical Isolation

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Thermal Headaches in Advanced LIGO Input Optics

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  1. Thermal Headaches in Advanced LIGO Input Optics Guido Mueller, Rupal Amin, David Guagliardo, David Tanner, and David Reitze Physics Department University of Florida Gainesville, FL LIGO-G010130-00-Z

  2. Input Optics Functions • RF Modulation • Mode Cleaning • Mode Matching • Optical Isolation • Distribution of Control Beams • Self Diagnostics

  3. dn aL P / 2 Kl dT The Challenge • Advanced LIGO will operate at 180W CW powers - “presents some challenges”: • Thermal Lensing --> Modal Degradation • z = z = 1 + i z • Thermally induced birefringence • FI- loss of isolation • EOM - spurious amplitude • modulation • Damage • Other (nonlinear) effects (SHG, PR) LiNbO3 at 30W: 5 x 5 x 40 mm LiNbO3 EOM - thermal lensing is: i) severe ii) position dependent

  4. Sample Characterization of thermal lensing Samples: TGG: Litton [111] 10 mm diameter, 20 mm length LiNbO3: Leysop, 5 x 5 x 40 mm Power Meter Lensing Measurement Dz HRM HRM l/2 Sample Glan Pol. Beam Scan l/4 HRM 50 W Nd:YLF Beam Dump HRM Power Meter D Sag Measurement l = 1053 nm NeNe PD -Ref. HRM DM l/2 Glan Pol. DM l/4 HRM PD - Signal Beam Dump

  5. Optical Path Difference Measurements Theory: Hello-Vinet P=50 W Absolute DL (hot - cold): 10 mm DOPD (1/e intensity): ~ 100 nm 250 nm @ 125W

  6. Optical Path Difference Measurements Mansell, et al., Appl. Opt., 2001

  7. Propagation Measurements I w(z)

  8. fh= fv= Propagation Measurements II 50 W Effective Thermal Lens

  9. 180 W EOM 1 EOM 2 EOM 3 Thermal Lensing in LiNbO3 • KTP does work; 300 W CW power, 1064 nm (H. Injeyan, TRW); • RTA should also work (lower loss tangent)

  10. E-O Modulation in Advanced LIGO Alternative Method: Mach-Zehnder modulation --> architecture problem Prototype developed for initial LIGO detectors, but not well characterized >> R&D effort

  11. dn dn dT dT dn dT M-1(z , z) Power Independent Compensation of Thermal Lensing aL P / 2 Kl z = z = 1 + iz a = absorption coefficient K = thermal conductivity

  12. Thermal Lensing Compensation Modeled using Melody 150 W FI or EOM

  13. Thermal Lensing Telescope • Similar to current LIGO Telescope • 2 mirror design (vacuum envelope constraints) • Accommodates wide range of mode matching parameters • All large (20 cm) optics • in-situ adjustment with feedback 532 nm 1064 nm Wide Bandgap Glass

  14. R&D Issues Still to be Faced • Modulator Development: • RTA performance • MZ modulation • Isolator Development: • Full FI system test (TCFI, EOT) • Possible thermal compensation (-dn/dT materials) • Telescope Development: • in-situ mode matching adjustment

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