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BEAM ALIGNMENT AND DRIFT OF OPTICS

BEAM ALIGNMENT AND DRIFT OF OPTICS. By: Stephanie Raymond LSU / Millsaps College with Gabriela Gonzalez and Ken Watts. 12 Nov 2003 LIGO-G030597-00-Z. PURPOSE. Aid initial alignment by providing a visual configuration for the operator, supplementary to WFS and dithering.

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BEAM ALIGNMENT AND DRIFT OF OPTICS

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  1. BEAM ALIGNMENT AND DRIFT OF OPTICS By: Stephanie Raymond LSU / Millsaps College with Gabriela Gonzalez and Ken Watts 12 Nov 2003 LIGO-G030597-00-Z

  2. PURPOSE • Aid initial alignment by providing a visual configuration for the operator, supplementary to WFS and dithering. • Compare the image of the beam on the optics during data taking • Determine good position of beam from a good lock • Monitor beams on optics and beams on photodiodes • Determine drift of the beams on the optics 12 Nov 2003 LIGO-G030597-00-Z

  3. Technique • Image Acquisition • Access channels (ETMX, ETMY, ITMX, ITMY, AS_PD, AS_Q, BS, and MC_TRANS) • Capture frames • Image Processing • Filtering • Fourier transform • Locate center of beam • Calculate correlation coefficient • Subtraction of images single-arm lock full lock 12 Nov 2003 LIGO-G030597-00-Z

  4. Outline of Software • Input reference image • Grab frame • Access video card • Select input channel • Run script • Process images • Fourier transforms • Difference image • Correlation coefficient • Display difference image with correlation coefficient • Clear workspace and repeat 12 Nov 2003 LIGO-G030597-00-Z

  5. Cropping • Have the option to disclude the OSEMs, but this sometimes clips the image of the beam • Centering method solves problem of change in luminosity of OSEMs affecting the correlatioin coefficient 12 Nov 2003 LIGO-G030597-00-Z

  6. Filtering MC_REFL • Commands • im2bw converts colorscale to grayscale to binary • medfilt2 eliminates “salt and pepper” noise • Information is lost to filtering • The purpose of filtering is to make viewing easier for the Operator input image im2bw medfilt2 12 Nov 2003 LIGO-G030597-00-Z

  7. Difference Image IFO_REFL • Order of operations is important in accurately displaying which direction the beam needs to move A C=fft(A) D-C ifft(D) B D=fft(B) 12 Nov 2003 LIGO-G030597-00-Z

  8. Fourier Transformvs.Simple Math Simple Subtraction of Images • Ignores intensity dependence • Reduces number of steps in image processing • Does not expedite script Fourier Transform • Prevents having to calibrate the intensity • Produces sharper image 12 Nov 2003 LIGO-G030597-00-Z

  9. For Example ETMY (single arm) • Reference Image 12 Nov 2003 LIGO-G030597-00-Z

  10. Cont. Example ETMY (single arm) 12 Nov 2003 LIGO-G030597-00-Z

  11. Quantitative and Qualitative Representations of Misalignment CORRELATION=79.62 CORRELATION=83.46 CORRELATION=85.17 CORRELATION=86.5 12 Nov 2003 LIGO-G030597-00-Z

  12. CONCLUSION • Fourier transform method successfully displays misalignment of beam relative to reference image during initial alignment • Develop beam center method that will be useful in monitoring drift of beam on optics • Data collected during S3 will determine extent if any to which beams on optics drift • Study correlations of beam position on AS_PD with data quality 12 Nov 2003 LIGO-G030597-00-Z

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