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 Mon Aug 3 13:10:46 2020, shruti, DailyProgress, Lab Work, Initial experiments and prep Tue Aug 4 14:08:44 2020, shruti, DailyProgress, Lab Work, Initial experiments and prep: Beam profile
Message ID: 2549     Entry time: Tue Aug 4 14:08:44 2020     In reply to: 2548
 Author: shruti Type: DailyProgress Category: Lab Work Subject: Initial experiments and prep: Beam profile

Notice of lab entry: I will be at the cryo lab for a few hours today (04 Aug 20) afternoon

Update:

## Beam profile results [razor-blade method]

At a few locations along the beam I measured the vertical and horizontal beam radii by measuring the power at different positions of blade edge across the beam. The power measured at the photo-diode was fitted with  $a + b \times {\rm erf}(\sqrt{2}(x-x_0)/w_z))$ where $w_z$ is the beam radius at the location along the beam and $x$ was either the horizontal or vertical position of the blade.

### Results:

The standard deviation as estimated from the fits are lower than $\pm$0.002 mm for all estimated radii.

But with the crude nature of the setup and not having the laser temperature stabilized (resulting in power drifts while taking readings), I guess that the error in each measurement is higher. The data in Attachment 3 also has recorded the resistance of the temperature sensor at different points while taking the data.

 Distance [in.] Horizontal radius [mm] Vertical radius [mm] 5 $\pm$ 0.1 0.120 0.121 6 $\pm$ 0.1 0.146 0.150 7 $\pm$ 0.1 0.175 0.173 8 $\pm$ 0.1 0.203 0.200 9 $\pm$ 0.1 0.231 0.229

- Attachment 1 has the updated setup with the clamped translation stage

- Attachment 2 shows the measured points with the error function fits. The offsets between the different curves along the x-axis are arbitrary.

- Attachment 3 shows a linear fit and an estimated divergence angle. I've assumed that all points I measured are outside the Rayleigh range, i.e., away the beam waist. The caption '5H' means that this set of data was taken 5 inches away from the output coupler (fibre-to-free space) moving the blade in the horizontal direction.

- Attachment 4 has all the data and jupyter notebook with analysis

- Attachment 5 shows the beam spot on the view card

 Attachment 1: IMG_0268.jpg  2.834 MB  Uploaded Thu Aug 6 14:07:36 2020
 Attachment 2: Erf.pdf  20 kB  Uploaded Thu Aug 6 14:11:07 2020
 Attachment 3: Div.pdf  13 kB  Uploaded Thu Aug 6 14:11:16 2020
 Attachment 4: beamprofdata.zip  109 kB  Uploaded Thu Aug 6 14:11:40 2020
 Attachment 5: IMG_0258.jpg  2.202 MB  Uploaded Thu Aug 6 14:23:22 2020
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