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Old Mar 27th 2018, 06:28 AM   #1
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Laser Experiment

So, I am trying to develop an experiment to measure the size of a laser's dot on a target under various conditions. The method we current use involves a camera focused on the laser's target to record the dot's changes. This method is fine, but it requires precise camera/target alignment and some maths based on the placement. The goal is to get a setup that is less time consuming and more repeatable. For this reason, I was thinking that shinning the laser on the front side of the target and having a camera attached to the backside of the target to measure the size from behind the target. This would allow the camera to remain at a fixed distance from the target, so the maths are repeatable, and ensure that the camera does not get in the way of possible laser variations.

My question then is, what would be a good material to use as the target to allow the camera on the backside to get a good view of the laser's dot with as little of distortion as possible? I am open to other dot measuring methods as well.
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Old Apr 12th 2018, 02:28 AM   #2
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Anything with a clean, shiny, polished surface should suffice. That will minimise scatter.
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Old Apr 12th 2018, 03:20 AM   #3
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From your post I understand you want to shine a laser on the front of a screen and measure the dot size by viewing the back of the screen ... that does sound like the best idea ....

For low power , sheets of white paper work well , can use multiple sheets together if required ....

High power might blow a hole in the paper , which will give you a permanent record of the size , maybe pulse the laser for a very short time ....

The dot will get bigger the further you are from the laser the beam is not parallel .. the better the quality of laser , the less it will diverge.
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Old Apr 12th 2018, 02:49 PM   #4
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One of the issues will be avoiding damaging the camera with the intensity of the laser light.
For telescopic viewing of the sun, astronomers use special solar filters.
Possibly one of these filters would make a suitable target, allowing enough light through for the camera to detect, but not enough to damage it.
A sheet of Mylar is commonly used as as solar filter

I have just had a quick Google and found several solar filters made from several different materials.
The hard core astronomical filters can get a bit expensive, but several "do-it-yourself" kits were shown at prices that seem reasonable enough to try out and not be too out of pocket if they fail.
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Old Apr 13th 2018, 01:45 AM   #5
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An alternative that might work is to draw an accurate grid on the target.
This grid would be large enough to fall outside the maximum spot size,
but small enough to fall inside the camera range of view.

The images taken would then include both the laser spot and the grid.
The grid could be used to calibrate each image, and thus the spot size could be determined.
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Old Apr 13th 2018, 07:49 PM   #6
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If these lasers are below 1 Watt in power , they will not burn a hole in paper , ordinary graph paper would be fine with 2 or 1 mm line spacing ...

Put the front surface of the paper with lines , facing the camera , the laser shines on the back of the paper ...no need for any filters on the camera ... some light will pass through the paper showing as a dot on the side of the paper with lines on.

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Old Apr 16th 2018, 12:24 PM   #7
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Note that having an accurate grid on the target, from which the camera can be calibrated, will work from a front viewing camera removing the requirement for a rear viewing camera.
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