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Laser Adaptive Optics for Advanced LIGO Liang Zhang with Malik Rakhmanov, Joe Gleason David Tanner, David Reitze, Guido Mueller University of Florida LIGO Group Optics Session 3/17/2004 LIGO-G040090-00-Z 1 Acknowledgement NSF Lonnie Houck Derek Kennedy Jinho Lee Christina Leidel Rachel Parks Luke Williams Wan Wu 3/17/2004 LIGO-G040090-00-Z 2 Outline Introduction Theory Experiment Future Work Conclusion 3/17/2004 LIGO-G040090-00-Z 3 Optical configuration of Advanced LIGO 3/17/2004 LIGO-G040090-00-Z 4 Input Optics subsystem 3/17/2004 LIGO-G040090-00-Z 5 Schematic layout of adaptive-lens mode matching telescope Nd:YAG Laser beam Adaptive lens HBS1 (OG515) HBS2 Mirror 1 Heating Beam Mirror 2 3/17/2004 LIGO-G040090-00-Z 6 Transmittance of SCHOTT glass OG515 1.0 514nm (Argon) 0.5 0.0 200 1064nm (Nd:YAG) 500 1000 (nm) Thickness: 3 mm (sample) Thickness: 15mm (experiment) 3/17/2004 LIGO-G040090-00-Z 7 Thermal lensing in OG515 Argon laser beam YAG laser beam OG515 An Argon laser is used as heating beam; a YAG laser is used to ‘read’ the thermal lensing effect of OG515. 3/17/2004 LIGO-G040090-00-Z 8 Optical path length (OPL) change due to thermal effects Temperature-dependent refractive index dn OPL (r ) LT (r ) dT Thermal Expansion OPL (r ) (n 1) LT (r ) : coefficient of thermal expansion . 3/17/2004 Photo-elastic Effect LIGO-G040090-00-Z 9 Theoretical calculation of temperature profile (from J. Lee and R. Parks (UF)) r Boundary Conditions: T T z R z 4P T (r , z ) 2 2 n 1 KR w L R 0 2 e r R 0 z 0, L 0 r 2 w2 r J 0 k n r dr r R J f n ( z) 0 kn ( J1 (k n )) 2 R P: power of the incident light : absorption coefficient K: thermal conductivity w: beam radius R:radius of OG515 k ( n ) L ( kRn ) L kn k R e 1 1 R z e R 1 Rn z z f n ( z) e e e k L k n 2 k n 2 kn L 2 n 2 ( ) e R 1 e R 1 R 3/17/2004 LIGO-G040090-00-Z 10 Theoretical temperature profile P (Argon laser): 6W 3/17/2004 T(room temperature): 293K. LIGO-G040090-00-Z 11 Theoretical OPL 3/17/2004 LIGO-G040090-00-Z 12 Experimental Setup R4 Argon Laser Polarizer Single-Mode Fiber R3 R2 M2 Nd:YAG Laser F1 M3 M4 R1 F2 M1 Faraday Isolator M5 Beam Scan R5 Beamsplitter OG515 M1, M2, M3, M4, M5 are lenses; R1, R2, R3, R4, R5 are mirrors; F1 and F2 are fiber-optic couplers The diameter of collimated Argon laser beam is 16 mm; the diameter of YAG laser on OG515 is 2mm. 3/17/2004 LIGO-G040090-00-Z 13 Experimental results P( Ar ) Thermal Lensing Beam Diameter of YAG (um) 2450 0W 2350 4W 2250 6W 2150 8W 2050 1950 1850 -30 3/17/2004 -20 -10 0 10 20 Distance from OG515 (inch) LIGO-G040090-00-Z 30 14 Focal length of adaptive lens Power of Heating beam (W) 3/17/2004 LIGO-G040090-00-Z 15 Beam Profile Without thermal lensing With thermal lensing The thermal lens doesn’t introduce large amplitude higher order Gaussian modes. 3/17/2004 LIGO-G040090-00-Z 16 Future work OG515 in a vacuum chamber will be tested. Fabry-Perot cavity will be used to measure higher order modes mode matching. Bullseye wavefront sensor will be used to measure and correct mode-matching. 3/17/2004 LIGO-G040090-00-Z 17 Conclusion A variable thermal lens is formed using different powers of a pumping beam. It is possible to control this variable lens to compensate the thermal lensing effects of the optical elements in advanced LIGO. 3/17/2004 LIGO-G040090-00-Z 18