Laser beam diagnostics :BEAMDIAG program.

Stéphan Del Burgo

CERN PS/LP

30 January 1998

DBS 01/98-101

Laser beam diagnostics : BEAMDIAG program.

• What is it for and where is it used ?

• How does it work ?

• The analysis with the main functions :

barycentre, contours, profiles,

widths, fits, 3-D…

• Conclusion - Next developments. DBS 01/98-102

• What is it for ?• For laser beam diagnostics and analysis.• To improve laser adjustments and beam

geometry.• For every kind of beams that a video

camera can see with or without a screen.

• Where is it used ?• In the CTF Laser room.• In the photocathodes laboratory.• In the new laser laboratory.

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• How does it work ? Depending on the wavelength, a video camera looks at a screen or directly at the beam. The video camera is triggered. The pulse ( a few ns or ps ) is seen only during one frame ( two interlaced frames usually ! ).

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• How does it work ?

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The data are acquired by a frame grabber in the PC. The frame grabber subtracts the noise from the picture. The frame grabber output is a TIFF file matrix in the PC. Each line of the matrix corresponds to one line of one frame, one line of the CCD matrix out of two.

All these developments have been done by

Eric CHEVALLAY.

• How does it work ?

My work begins here with the calculations on the matrix.

The size of the matrix can be very large ( e.g. 512x256 ). The calculations are made with Matlab, Matlab 5 for the last version.

The program is called BEAMDIAG ( or BEAMCTF ).

This program contains around 80 files .

The main loop is :

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Display

Data Acquisition ( TIFF file )

Conversion into an Intensity Matrix

Calculations and Analysis1 loop : ~15 s

• Calculations and Analysis :– The projections from the beam to the screen and the

camera are compensated ( X scale = Y scale ).– Matrix conversion and normalization :

DB

S 0

1/9

8-1

07

11 16 35 5

3 125 78 11

204 204 12 16

202 251 121 11

0

1

2

254

255

... ... ... ...

R G BLUT

TIFF Matrix

Intensity Matrix

Video picture : 2 frames

0 0 0

0.1 0 0

0.2 0 0

1 1 0.9

1 1 1

0 01 1

0.2 0.3

0.05 0.5

0.33 0.1

0.6 0.2

0.9 0.9 0.23 0.3

0.7 0.95 0.42 0.2

Level Level

Pixels Pixels100 100

Histogram HistogramNormalization

• Analysis - video matrix, contours, barycentre, profiles

DB

S 0

1/9

8-1

08

• Analysis - normalized matrix, maximum, integrated profiles

DB

S 0

1/9

8-1

09

• Analysis - normalized, barycentre, personal, length

DB

S 0

1/9

8-1

10

• Analysis - normalized, barycentre, gaussian fit

DB

S 0

1/9

8-1

11

• Analysis - normalized, barycentre, gaussian fit, real beam

DB

S 0

1/9

8-1

12

• Analysis - normalized, 3-D

DB

S 0

1/9

8-1

13

• Conclusion - Next developments.

• Last version of the laser beam analysis program with Matlab 5. User friendly.

• Adaptation from Windows 3.1 to Windows 95, and finally from Matlab 4 to Matlab 5 It runs better ( display speed, printing, saving,... ).

• Still a little bit slow.• Good results for the analysis ( widths, fits,… ). Reliable if

correct calibration !

• Possible to add other specific functions :» different fits» remote control for the aperture

• Next version with VME technology...

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