20130129 Laser Characterisation

The usual characterisation of a telescope calibration followed by an M2 at the chosen telescope position was undertaken on 20130119 by KK. This was repeated again by LN on 20130129. The results of the second characterisation are detailed herein.

Telescope Calibration

• The telescope position was varied at about 10 points and 64 images recorded at full laser power
• It was confirmed that although the laser beam size changed, the position did not

Telescope Calibration 4Sigma:

Telescope Calibration ISO 4Sigma:

A telescope setting of 14mm was chosen to give approximately 4 sigma of 12mm in the vertical dimension. Below is the beam profile at the VIP at this setting.

Beam Profile at Chosen Telescope Setting:

M2

• 64 images were recorded at each stage position
• ND filters were used in combination directly in front of the camera
• The number of ND filters was minimised
• Background subtraction was performed each time the capture block on the camera was changed
• The filter in the trigger settings was used to only record images with the ADC between 75 and 95% peak
• The stage was positioned at approximately 0 on it's marker (by eye - no homing procedure - but relative distance precise)
• Positive position values correspond to further away from the lens and negative towards the lens
• The lens has a focal length of 1.677m at a wavelength of 532nm
• The laser was operated at 100us flash lamp delay - full power

In the end, even with a quick scan through it's hard to judge where the exact focus is and due to the astigmatism the focal region is longer than you would normally expect. Therefore, more data points were recorded around the focal region and with the benefit of 3Hz operation now, this didn't take too long.

New analysis software is used. The Labview dataray data extractor has been modified to prepare an additional text file that records some settings in a defined file format that can be used by the python analysis software for fitting the M2.

• A file near the edge of the M2 scan was used to ascertain the approximate angle for the analysis.
• Several dataray job files were saved with different crosshair angles
• The Labview data extractor was used with each job file

• Analysed data is stored automatically in extlw/msq/YYYYMMDD_HHMM/ where the time is the current time the file is analysed
• The files inside this directory have the job filename as part of their name

The following commands were used for anslysis:

pylab
import lwAna3
lwAna3.Laser.DefaultAnalysis('../dat/msq/20130204_2257/')

repeated for different job files -> different directories

lwAna3.Fit.SelectLaserPropagationFile('../dat/msq/20130205_0530/fit_parameters_input.dat')

Below are the graphs of the various fits and the last one, -15.1 degrees was chosen. For this file, the data scaled to the laserwire lens focal length is shown as well as the model the fitting program will use -> ie two different M2 models and their combined projection into the lab vertical.

It should be noted, that this would appear to not be the best M2 data. Although care was taken, even greater care will need to be taken for the best possible data. Particular care should be taken to ensure the same relative capture block size to the laser beam as much as possible.

-5.0 Degrees

-7.4 Degrees:

-10.2 Degrees:

-14.2 Degrees:

-15.1 Degrees:

-15.1 Degrees Scaled:

-15.1 Degrees Projected: