Beam alignment and drift of optics
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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

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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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