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measuring divergence

Hyperion

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hi all

i'm doing an extensive review of my Rayfoss 250 and i had to measure its divergence.
to do this i had to measure the diameter of the dot.
so the question is: looking at this photo (the photo shows the dot at 10 meters), had i to measure the diameter of the white area or of all the dot?



which is the diameter of the dot in the photo?

many thanks :)
Alessandro
 

lasersbee

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Use a pair of safety goggles for 532nm and you will see the actual
size of the beam on a surface... It is difficult to see with the naked
eye.

BTW I hope you are using Laser Safety Goggles while operating a
250mW Laser...:eek:


Jerry
 

Hyperion

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measure the whole dot and calculate through here
pseudonomen137's JScript mRad Calculator
so in this photo the diameter should be ~18mm ?

Use a pair of safety goggles for 532nm and you will see the actual
size of the beam on a surface... It is difficult to see with the naked
eye.

BTW I hope you are using Laser Safety Goggles while operating a
250mW Laser...:eek:


Jerry
of course, i use my safety goggles :p
but taking a photo to the dot the measurement should be more accurate, right?
 

lasersbee

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No.... as I posted above... the actual beam diameter is known
when looking at the dot through Laser Safety Goggles only...
and not with a Camera or the naked eye...

Does the dot through your safety goggles have the same diameter
as the dot in the photo....:thinking:


Jerry
 
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lasersbee

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I would imagine one could use a camera style shutter iris
(the circular type) and slowly close it manually until the Laser's
power drops..


Jerry
 

Hyperion

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Another way to measure it is to pass it through apertures of known diameter. Use smaller apertures until the power starts to drop. That's the beam diameter.
are you sure this method works?
the dot is more concentrated in the center...
moreover using this method i cannot get the diameter at the aperture.
 

RA_pierce

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A useful method I have come up with (and I'm sure others have as well) is to average the spot size measuring the "hot spot" and the entire beam, including the dimmer region.

I measure both, average them, and use that for calculations.
It's very difficult to get an accurate measurement with a Gaussian beam.
 

Cyparagon

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IIRC, the proper diameter measurement contains 100(1-e^-2)% {which is about 86%} of the beam's power.

Edit: I was close. See this page.
 

Hyperion

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first of all, thanks of all these replies :)

i haven't an iris diaphram...
anyway it's not possible to get the divergence using a laser power meter beacause the power of a green DPSS laser is not constant. so you cannot say: "this is 86% of the power"

maybe the better way to get these data is, as RA_pierce said, averaging the diameter of the spot...

any other advices?
 
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i haven't an iris diaphram...
anyway it's not possible to get the divergence using a laser power meter beacause the power of a green DPSS laser is not constant. so you cannot say: "this is 86% of the power"
not trivial != not possible. You dismiss it much too easily.

 
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this statement hasn't added any information :thinking:
You said:

i haven't an iris diaphram...
anyway it's not possible to get the divergence using a laser power meter beacause the power of a green DPSS laser is not constant. so you cannot say: "this is 86% of the power"
So I replied:

not trivial != not possible. You dismiss it much too easily.

You say it's not possible, but it is possible. It is absolutely 100% possible. However, it is not trivial, which is what I was saying. Just because it's not easy doesn't mean you can't do it. That's all I'm trying to say, is that you dismiss the idea too easily, when it's perfectly possible.
 

Hyperion

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this is a power graph i made of my laser.
as you can see, the variation of the power is too high to do an accurate measurement.
probably measurring the power through a diaphram is the best solution for a blu-ray, a red or an ir laser but not with a green one.
 
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Yep, that chart looks difficult. Not easy. But not impossible either.

You said it isn't possible, I said it is. That is all.
 




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