Angular Noise in a Suspended Interferometer with DC Readout Royal Reinecke Co-Mentors: Alan Weinstein and Rana Adhikari

Overview Introduction to LIGO What are optical levers and how do they work? Angular noise sources –Servo-induced Noise –Electronic Noise –Laser Intensity Noise Overall Noise Budget

Advanced LIGO X Arm Y Arm Michelson Interferometer Fabry Perot Arm Cavities Core optics controlled by optical levers SRM OMC

Optical Levers Oplev Laser QPD Suspended Optic

Initial Jitter Seen by Oplevs X Arm of 40 mY Arm of 40 m Apparent noise floor between and radians above ~5Hz Amplitude Spectral Density

Servo Digital Filters Old ELP40 (blue) New ELP35 (red) Coil Drivers

Effects of Filter Change on Actual Mirror Motion X ArmY Arm

Electronic Noise Electronic Noise larger than actual mirror motion above 5 Hz Amplify QPD signal before noisy ADC stage

Electronic Filters Whitening Filter -20dB at 8192 Hz Falls as 1/f 2 Zero at 1Hz Poles at 10Hz, 1500Hz Low Pass Filter

Before and After Whitening ETMX previous ETMY previous

Effect of Filters ETMX Pitch Error and Out Signals (old-blue, new-red)

Laser Intensity Noise Apparent Mirror Motion due to Laser Intensity Fluctuations

Transfer Function of Input Voltage to Output Laser Power

Optical Lever Noise Budget

Acknowledgments Alan Weinstein and Rana Adhikari 40m Staff LIGO NSF Caltech SURF Program