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 Sun May 26 21:47:07 2019, Kruthi, Update, Cameras, CCD Calibration Sat Jun 29 03:11:18 2019, Kruthi, Update, Cameras, CCD Calibration Sun Jul 14 00:24:29 2019, Kruthi, Update, Cameras, CCD Calibration
Message ID: 14639     Entry time: Sun May 26 21:47:07 2019     Reply to this: 14708
 Author: Kruthi Type: Update Category: Cameras Subject: CCD Calibration

On Friday, I tried calibrating the CCD with the following setup. Here, I present the expected values of scattered power (Ps) at $\theta$s = 45°, where $\theta$s is scattering angle (refer figure). The LED box has a hole with an aperture of 5mm and the LED is placed at approximately 7mm from the hole. Thus the aperture angle is 2*tan-1(2.5/7) ≈ 40° approx. Using this, the spot size of the LED light at a distance 'd' was estimated. The width of the LED holder/stand (approx 4") puts a constraint on the lowest possible $\theta$s. At this lowest possible $\theta$s, the distance of CCD/Ophir from the screen is given by $\dpi{80} \sqrt{d^2 + (2'')^2}$. This was taken as the imaging distance for other angles also.

In the table below, Pi is taken to be 1.5mW, and Ps and $\Omega$ were calculated using the following equations:

$\dpi{80} \Omega = \frac{CCD \ sensor \ area}{(Imaging \ distance)^2}$            $\dpi{80} P_{s} = \frac{1 }{\pi} * P_{i} *\Omega *cos(45^{\circ})$

 d (cm) Estimated spot diameter (cm) Lowest possible $\theta$s  (in degrees) Distance of CCD/Ophir from the screen (in cm) $\Omega$ (in sr) Expected Ps at   $\theta$s = 45° (in µW) 1.0 1.2 78.86 5.2 0.1036 34.98 2.0 2.0 68.51 5.5 0.0259 8.74 3.0 2.7 59.44 5.9 0.0115 3.88 4.0 3.4 51.78 6.5 0.0065 2.19 5.0 4.1 45.45 7.1 0.0041 1.38 6.0 4.9 40.25 7.9 0.0029 0.98 7.0 5.6 35.97 8.6 0.0021 0.71 8.0 6.3 32.42 9.5 0.0016 0.54 9.0 7.1 29.44 10.3 0.0013 0.44 10.0 7.8 26.93 11.2 0.0010 0.34

On measuring the scattered power (Ps) using the ophir power meter, I got values of the same order as that of  expected values given the above table. Like Gautam suggested, we could use a photodiode to detect the scattered power as it will offer us better precision or we could calibrate the power meter using the method mentioned in Johannes's post: https://nodus.ligo.caltech.edu:8081/40m/13391.

 Attachment 1: CCD_calibration_setup.png  14 kB  Uploaded Mon May 27 00:28:13 2019
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