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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

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
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

technique
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

outline of software
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

cropping
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

filtering mc refl
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

difference image ifo refl
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

fourier transform vs simple math
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

for example etmy single arm
For Example ETMY (single arm)
  • Reference Image

12 Nov 2003 LIGO-G030597-00-Z

cont example etmy single arm
Cont. Example ETMY (single arm)

12 Nov 2003 LIGO-G030597-00-Z

quantitative and qualitative representations of misalignment
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

conclusion
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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